This is fascinating hot stuff:
http://www.theregister.co.uk/2007/12/11/bo...l_laser_fitted/
Been there, some real cool stuff I gotta say 
If I had a nifty new toy like that,, I would love to take it out for a test drive.
I sure wondered about that missile that North Korea launched last year, that for some strange reason it just tumbled into the sea of Japan. Hummmm. could it be?
I sure wondered about that missile that North Korea launched last year, that for some strange reason it just tumbled into the sea of Japan. Hummmm. could it be?
As far as I know, they're still trying to cram the laser into the 747, so it's more likely, IMO, that the NKoreans simply didn't have the missile built right.
I work for a company that builds rocket engines, and it's trickier than it looks.
I work for a company that builds rocket engines, and it's trickier than it looks.
Wcelliott, how practical is this idea of putting a laser cannon into practice in a blank? I need not say what the blank represents for obvious reasons and you can figure it out.
http://www.physorg.com/news130511435.html
The top story here offers help to the U.S. economy in the way of titanium powders at a reasonable cost. The military is beaming over this technique as mentioned. The car industry can use JIT inventory to exactly match the parts produced from this technique. Both military and car industries will benefit tremendously by lowering prices down the board and boosting economy.
Laser cannons are obviously a possible beneficiary without need to mention, but I did.
The top story here offers help to the U.S. economy in the way of titanium powders at a reasonable cost. The military is beaming over this technique as mentioned. The car industry can use JIT inventory to exactly match the parts produced from this technique. Both military and car industries will benefit tremendously by lowering prices down the board and boosting economy.
Laser cannons are obviously a possible beneficiary without need to mention, but I did.
QUOTE (midwestern+May 20 2008, 06:01 PM)
Wcelliott, how practical is this idea of putting a laser cannon into practice in a blank? I need not say what the blank represents for obvious reasons and you can figure it out.
Is this what you mean by blank?
http://www.youtube.com/watch?v=9KU_JqTZHRU
Maybe could be used for a DIY blank?
Is this what you mean by blank?
http://www.youtube.com/watch?v=9KU_JqTZHRU
Maybe could be used for a DIY blank?
Ayyyyyy. Great to know some are clueless is comforting.
If by "blank" you mean "satellite", I worked on the Space Based Laser for three years before it was cancelled.
I could go into greater detail about why it was cancelled, but let's just say that "Dilbert" cartoons are more fact-based than most people would believe.
If you're thinking about putting the SBL laser on a ship, it only works in a vacuum.
If you're talking about putting it on an airplane, it's called "AirBorne Laser", and that's what they're having trouble cramming into a 747.
There are other tactical lasers, but they don't have the range or power to destroy IRBMs (yet).
The likeliest answer to the NKorean missile failure is that it's harder to make missiles work than most tin-pot dictators seem to think. (The same is true of high-energy missile-defense radars.)
I could go into greater detail about why it was cancelled, but let's just say that "Dilbert" cartoons are more fact-based than most people would believe.
If you're thinking about putting the SBL laser on a ship, it only works in a vacuum.
If you're talking about putting it on an airplane, it's called "AirBorne Laser", and that's what they're having trouble cramming into a 747.
There are other tactical lasers, but they don't have the range or power to destroy IRBMs (yet).
The likeliest answer to the NKorean missile failure is that it's harder to make missiles work than most tin-pot dictators seem to think. (The same is true of high-energy missile-defense radars.)
Airborne Laser testing
More ABL testing
ABL and Hanscom Air Force Base
I worked at Hanscom, at the MIT Lincoln Laboratories where that work is being done, although in a different group.
It's is a pretty cool idea, and the big Jet at that little airport looks like Gulliver.
More ABL testing
ABL and Hanscom Air Force Base
I worked at Hanscom, at the MIT Lincoln Laboratories where that work is being done, although in a different group.
It's is a pretty cool idea, and the big Jet at that little airport looks like Gulliver.
Okay, the vacuum answer is the one I'm searching for all along wcelliott. 
Actually, the Soviet's spent time and money developing a version of a space-based laser that used technology that *could* be used at sea level (non-vacuum), but to the best of my knowledge, we don't have any ship-based directed-energy weapons capable of shooting down a missile.
I hesitate to mention it and fuel speculation, but for honesty's sake, the technology is feasible, whether it was developed or not is something I wouldn't know.
I still feel that it was more likely a simple matter that missiles aren't as easy to build and as reliable the NKoreans might seem they are.
I hesitate to mention it and fuel speculation, but for honesty's sake, the technology is feasible, whether it was developed or not is something I wouldn't know.
I still feel that it was more likely a simple matter that missiles aren't as easy to build and as reliable the NKoreans might seem they are.
Thanks for understanding the hesitation and the answers.
Thanks for understanding my hesitation in answering.
Laser weapons are completely impractical, even if you could miniaturize a super powerful laser enough to put it on a satellite or aircraft.
In order to be effective, you must have pinpoint accuracy AND you must be able to maintain pinpoint accuracy long enough for the laser to deliver enough energy to detonate the target missle or craft's explosive payload or fuel tanks. Which means the aim must be held for several seconds or even minutes to bring down the target.
When attempting to shoot down an enemy missle, it makes far more sense to use Rail Guns, or another missle. But rail gun technology has also been very hard to miniaturize.
In order to be effective, you must have pinpoint accuracy AND you must be able to maintain pinpoint accuracy long enough for the laser to deliver enough energy to detonate the target missle or craft's explosive payload or fuel tanks. Which means the aim must be held for several seconds or even minutes to bring down the target.
When attempting to shoot down an enemy missle, it makes far more sense to use Rail Guns, or another missle. But rail gun technology has also been very hard to miniaturize.
Good one wcelliott.
QUOTE
Laser weapons are completely impractical, even if you could miniaturize a super powerful laser enough to put it on a satellite or aircraft.
In order to be effective, you must have pinpoint accuracy AND you must be able to maintain pinpoint accuracy long enough for the laser to deliver enough energy to detonate the target missle or craft's explosive payload or fuel tanks. Which means the aim must be held for several seconds or even minutes to bring down the target.
When attempting to shoot down an enemy missle, it makes far more sense to use Rail Guns, or another missle. But rail gun technology has also been very hard to miniaturize.
In order to be effective, you must have pinpoint accuracy AND you must be able to maintain pinpoint accuracy long enough for the laser to deliver enough energy to detonate the target missle or craft's explosive payload or fuel tanks. Which means the aim must be held for several seconds or even minutes to bring down the target.
When attempting to shoot down an enemy missle, it makes far more sense to use Rail Guns, or another missle. But rail gun technology has also been very hard to miniaturize.
You're right on all counts, but technology has a way of surprising people. I worked on the Space Based Laser program for three years, and the problems you identified were all addressed (with lots of money). The main problem we couldn't overcome was the fact that the Missile Defense customer wanted three contractors to work together as a team, and that part never worked. Each contractor wanted half the money and total control of the program. It was more intrigue than engineering, everyone jockeying for position. The customer finally came to his senses and cancelled the program. We could've built the system, there were no technical problems we couldn't overcome, but the politics that comes along inevitably with a multibillion dollar program killed it.
I was also involved in the development of a Kinetic Kill Vehicle interceptor, which was a much smaller program, but was successful in all its tests. It turns out to be less like "hitting a bullet with a bullet" than running a motorcycle into a delivery truck, which if you've ever driven a motorcycle, you know is much simpler to do than others might think.
I still believe, though, that the NKoreans simplyunderestimated the difficulty of making a missile work. (And if I'm going to support any conspiracy theory, it's also a lot easier to sabotage a missile than the NKs realized.)
Thanks for sharing your knowledge wcelliott. Politics are a hindering factor of what needs to be accomplished as well. 
I can't imagine a tactical laser being a useful tool in the foreseeable future, not when a small piece of lead will work just as well for a fraction of the cost, and lead tends not to be broken up by fog and dust.
Also, isn't any Laser Anti Missile System really easy to defeat, by simply making the missiles reflective and spinning? Reduce the absorbed energy, and spin to spread it out. Or am I completely missing the point?
Also, isn't any Laser Anti Missile System really easy to defeat, by simply making the missiles reflective and spinning? Reduce the absorbed energy, and spin to spread it out. Or am I completely missing the point?
QUOTE
I can't imagine a tactical laser being a useful tool in the foreseeable future, not when a small piece of lead will work just as well for a fraction of the cost, and lead tends not to be broken up by fog and dust.
Also, isn't any Laser Anti Missile System really easy to defeat, by simply making the missiles reflective and spinning? Reduce the absorbed energy, and spin to spread it out. Or am I completely missing the point?
Also, isn't any Laser Anti Missile System really easy to defeat, by simply making the missiles reflective and spinning? Reduce the absorbed energy, and spin to spread it out. Or am I completely missing the point?
Tactical lasers aren't designed as anti-personnel weapons, you're correct about the cost of bullets versus the cost of laser shots, but they are useful for things like incoming missiles which would otherwise do a lot of damage to our side.
Google "THEL" (Tactical High-Energy Laser).
The "spinning-shiny missile" idea has been around since SDI (mid-80's). Can you think of any examples? Me, neither. Even spinning-shiny missiles have inherent vulnerabilities, features that can't be shiny, for instance. Spinning inherently degrades accuracy, and you can only make things like missiles so shiny, they'll still absorb *some* of the energy incident on them, so if and when someone fields one of those spinning-shiny missiles, we'll up the power of our lasers.
I once had a professor who's dream was to live long enough to see manned lasers orbiting the earth as a defense system (missiles and the like, not aliens). He was of the opinion that the first nation to put such a system into widespread application would achieve a high degree of safety.
I never could tell if he was serious or if he was simply trying to get us thinking.
I never could tell if he was serious or if he was simply trying to get us thinking.
I think the baseline SDI concept was *unmanned* lasers in orbit. People are so needy, they're a great liability in spacecraft. It ends up being 95% life-support, 5% payload. You can still keep "a man in the loop" by putting a TV camera on the unmanned spacecraft and the Big Red Button at an underground manned workstation, safe from attack. (Safer, at least, than being in a spacecraft.)
I worked on SDI, and it was the unstated understanding of those involved in the R&D for it that it wouldn't work and wasn't a good idea, at least at that time and under those circumstances. It had too many obvious vulnerabilities, especially against the Soviet Union, which had thousands of ICBMs aimed at us, and even a small percentage of "leakage" would pretty much devastate the US. No system is 100% reliable, and a 99% reliable defense against 20,000 nukes doesn't make anybody sleep more soundly at night. Do the math, most people can't name the 200 largest cities in the US without their home town getting on the list.
I more recently worked on the Space Based Laser (for about three years), and I really would've liked to see it work. Times are different now, things have changed, and it's dubious that we'd have to face 20,000 nukes raining down on us, it's more likely that some country like NKorea might launch one or two short-range missiles with nuke warheads at SKorea or one of our aircraft carriers, and 99% of two targets destroyed is a lot better than nothing.
I worked on SDI, and it was the unstated understanding of those involved in the R&D for it that it wouldn't work and wasn't a good idea, at least at that time and under those circumstances. It had too many obvious vulnerabilities, especially against the Soviet Union, which had thousands of ICBMs aimed at us, and even a small percentage of "leakage" would pretty much devastate the US. No system is 100% reliable, and a 99% reliable defense against 20,000 nukes doesn't make anybody sleep more soundly at night. Do the math, most people can't name the 200 largest cities in the US without their home town getting on the list.
I more recently worked on the Space Based Laser (for about three years), and I really would've liked to see it work. Times are different now, things have changed, and it's dubious that we'd have to face 20,000 nukes raining down on us, it's more likely that some country like NKorea might launch one or two short-range missiles with nuke warheads at SKorea or one of our aircraft carriers, and 99% of two targets destroyed is a lot better than nothing.
Wcelliott, understandable numbers and percentages have taken SDI off the shelf. What if reintroduction of a "European-Eastern initiative were to regenerate the program? What are your thoughts? Would this be sound or not?
QUOTE
The "spinning-shiny missile" idea has been around since SDI (mid-80's). Can you think of any examples? Me, neither.
Well, no, but I think that's mostly because there no laser based AMS systems around either.
QUOTE (->
| QUOTE |
The "spinning-shiny missile" idea has been around since SDI (mid-80's). Can you think of any examples? Me, neither. |
Well, no, but I think that's mostly because there no laser based AMS systems around either.
Spinning inherently degrades accuracy, and you can only make things like missiles so shiny, they'll still absorb *some* of the energy incident on them, so if and when someone fields one of those spinning-shiny missiles, we'll up the power of our lasers.
Well, that's easier said then done. If you reflect 80% of the energy away, you need a laser 5 times as powerful, which I would think would be rather expensive. Or you would need to aim at the same spot a bit over 5 times longer, more when the target is spinning.
Though I'm just an astronomer, not a rocket scientist, I don't really see how a properly spinning missile would be less accurate. You could just make it spin when it's on target, then minor corrections wouldn't be to difficult. Besides, if we're talking about half a dozen half-megaton warheads per ICBM, it doesn't exactly have to be pinpoint accuracte.
Question though: What is the cost/efficacy of a laser system vs a missile system such as all ready (partly) in used in the Ground-Based Midcourse Defense on a strategic level, or THAAD on a tactical level. Is it worth developing a laser, when a missile will work just as well? I don't know the operating costs of either system, nor the efficacy, so I can't say anything useful on this. Anyone?
But, all technical difficulties aside, I recall the 1972 ABM-treaty that limits the amount of ABM's a country is allowed to have, to make sure MAD still functions, and nobody gets the idea of winning a nuclear war. Wouldn't this idea do the same?
EDIT: Oh, I just noticed the USA doesn't care much about said treaty, as they withdrew in 2002. Still, lets keep this about the tech, not the politics.
Alcari, I'm having a tough time thinking laser over missile defense too. This is why I'm asking the question to wcelliott.
Even if the missile was spinning, the heat would still build up on the missile, it would just be dispersed along a circumference of the missile. Depending on how long the laser has to be aimed at the missile to blow it up, it would be a matter of holding the beam on the missile for a longer period of time. This may or may not be practical depending on the time it takes to penetrate the hull of a non-spinning missile.
As for a reflective missile, well, if you leave a mirror out in the sun it will still warm up pretty fast, and I believe it won't take long for an amplified intensity of light to penetrate even the shiniest missile.
As for a reflective missile, well, if you leave a mirror out in the sun it will still warm up pretty fast, and I believe it won't take long for an amplified intensity of light to penetrate even the shiniest missile.
QUOTE
Alcari, I'm having a tough time thinking laser over missile defense too. This is why I'm asking the question to wcelliott.
You're asking some very intelligent questions, and I'd love to get into the discussion at this level, but I'm obliged to keep my mouth shut about some things, this being one of them.
I do remember reading someplace that a laser shot capable of downing a missile costs about $3000-worth of chemicals, and IIRC, a Patriot costs maybe a million or so. (??? If someone has a real cost figure, please advise, I'm guessing.)
Yeah, I thought that might be the case. Unfortunate, but understandable.
Oh well, on with the random speculation then
Well, it would take exact figures to find out the answer, as well as (most likely) classified information on how such a laser can maintain a beam, what the output is, whether it functions by melting a hole or by overheating the missile, etc etc etc.
Well, it would take exact figures to find out the answer, as well as (most likely) classified information on how such a laser can maintain a beam, what the output is, whether it functions by melting a hole or by overheating the missile, etc etc etc.
As for a reflective missile, well, if you leave a mirror out in the sun it will still warm up pretty fast, and I believe it won't take long for an amplified intensity of light to penetrate even the shiniest missile.
I wasn't talking about a mirror. Besides, home-and-garden mirrors are pretty bad at reflecting, especially in the infrared. Now, I realize a dielectric mirror would make the missiles prohibitively expensive*, but a reflective aluminum coating could reflect about 90% to 95% of infrared radiation, so it would take an output 10 to 20 times higher then for a non-reflective material.
You could even put an ablative stealth coating on top of it, so it wouldn't stand out like a cargo ship on radar. For that matter, what about an ablative anti-laser coating? Preferable something that produces large amounts of dust to break up the laser even more.
Tangent: Do re-entry vehicles free fall? If so, you could just surround them in a cloud of dust once they're on course.
Wikipedia says:
"The Patriot missiles cost between $1 and $3 million dollars per copy, depending on variant."
Of course, it's rather obvious that in sustained use a laser is much more cost effective, but they have to be developed, build, installed and maintained as well. Now, I'm sure the development of, say, the patriot system was horribly expensive as well, but I doubt it measures up to the vast mountains of cash poured into the different LAMS systems.
*A dinner-plate sized dielectric mirror, rated at 99.99% reflection in it's part of the spectrum, set the optical observatory nearby back about a quarter of a million euro, making it worth quite a bit more then it's weight in gold.
Oh well, on with the random speculation then
QUOTE
Depending on how long the laser has to be aimed at the missile to blow it up, it would be a matter of holding the beam on the missile for a longer period of time. This may or may not be practical depending on the time it takes to penetrate the hull of a non-spinning missile.
Well, it would take exact figures to find out the answer, as well as (most likely) classified information on how such a laser can maintain a beam, what the output is, whether it functions by melting a hole or by overheating the missile, etc etc etc.
QUOTE (->
| QUOTE |
| Depending on how long the laser has to be aimed at the missile to blow it up, it would be a matter of holding the beam on the missile for a longer period of time. This may or may not be practical depending on the time it takes to penetrate the hull of a non-spinning missile. |
Well, it would take exact figures to find out the answer, as well as (most likely) classified information on how such a laser can maintain a beam, what the output is, whether it functions by melting a hole or by overheating the missile, etc etc etc.
As for a reflective missile, well, if you leave a mirror out in the sun it will still warm up pretty fast, and I believe it won't take long for an amplified intensity of light to penetrate even the shiniest missile.
I wasn't talking about a mirror. Besides, home-and-garden mirrors are pretty bad at reflecting, especially in the infrared. Now, I realize a dielectric mirror would make the missiles prohibitively expensive*, but a reflective aluminum coating could reflect about 90% to 95% of infrared radiation, so it would take an output 10 to 20 times higher then for a non-reflective material.
You could even put an ablative stealth coating on top of it, so it wouldn't stand out like a cargo ship on radar. For that matter, what about an ablative anti-laser coating? Preferable something that produces large amounts of dust to break up the laser even more.
Tangent: Do re-entry vehicles free fall? If so, you could just surround them in a cloud of dust once they're on course.
QUOTE
I do remember reading someplace that a laser shot capable of downing a missile costs about $3000-worth of chemicals, and IIRC, a Patriot costs maybe a million or so
Wikipedia says:
"The Patriot missiles cost between $1 and $3 million dollars per copy, depending on variant."
Of course, it's rather obvious that in sustained use a laser is much more cost effective, but they have to be developed, build, installed and maintained as well. Now, I'm sure the development of, say, the patriot system was horribly expensive as well, but I doubt it measures up to the vast mountains of cash poured into the different LAMS systems.
*A dinner-plate sized dielectric mirror, rated at 99.99% reflection in it's part of the spectrum, set the optical observatory nearby back about a quarter of a million euro, making it worth quite a bit more then it's weight in gold.
It seems that nowadays, we are more concerned with a small terrorist cell gaining access to a nuclear device that they can deliver in more covert ways, yes?
and isnt it more likely they (the terrorist cells) will deliver that device via ground transport or water transport intead of a dramatic launch on a missile that probably does not have the capability of reaching any targets in the US?
Keep in mind that most of our current "enemies of the state" are looking for drama as well as destruction. 10 or 15 small nukes going off in LA, NY, Miami, or wherever would make the news much better than a missile getting shot down....
for whatever that is worth.
MM
and isnt it more likely they (the terrorist cells) will deliver that device via ground transport or water transport intead of a dramatic launch on a missile that probably does not have the capability of reaching any targets in the US?
Keep in mind that most of our current "enemies of the state" are looking for drama as well as destruction. 10 or 15 small nukes going off in LA, NY, Miami, or wherever would make the news much better than a missile getting shot down....
for whatever that is worth.
MM
Nikola Tesla started this, watch the youtube documentary videos on it:
Nikola Tesla: The Missing Secrets
Nikola Tesla: The Missing Secrets
That's ok wcelliott. Some things have to stay confidential. Your numbers seem accurate, indeed. This is why I ask the question.
Your numbers seem accurate, indeed. This is why I ask the question.
Of course, getting a nuke in in a shipping container, or a minivan is a hundred times better then launching a missile, if only because you can see where a missile is launched from.
But that's a little besides the point, as the thread was about Laser Anti Missile Systems, not How to nuke the USA
But that's a little besides the point, as the thread was about Laser Anti Missile Systems, not How to nuke the USA
QUOTE (thinker+Jun 22 2008, 10:20 PM)
Even if the missile was spinning, the heat would still build up on the missile, it would just be dispersed along a circumference of the missile. Depending on how long the laser has to be aimed at the missile to blow it up, it would be a matter of holding the beam on the missile for a longer period of time. This may or may not be practical depending on the time it takes to penetrate the hull of a non-spinning missile.
Is everyone here assuming that the laser would have zero divergence??? From my experience, if you were gonna shoot down an ICBM with a laser, it would be at long range, and over that kind of range you'd be lucky to have a spot with a diameter of less than about 20-30m diameter. A spinning missile would have very little effect I suspect.
And tracking a missile is trivial. It is currently employed in laser systems which shoot down missiles at very short ranges, i.e. much larger angular velocities, so would certainly not be a problem with an ICBM.
The biggest problem is power and atmospheric power losses, AFAIK.
Ah right... I forgot to to include the duration of the pulse. Of course if it's so short, you'd have to spin the missile at insane speeds in order for it to have an effect. Still, a reflective mirror seems to be a very cheap countermeasure against such a weapon, unles the output of the laser is allready several orders of magnitude higher than needed.
I have exactly zero experience with chemical lasers, but I asume they are quite capable of projecting an almost perfectly straight beam. So you would only have to deal with atmospheric scattering. A few kilometers isn't that far at the speed of light.
As for divergence, if the "business end" of the beam is a 20 meter diameter spot, wouldn't that be a massive waste of energy? If the spot were, say, 5cm (random guess), the ammount of energy required to reach the same effect would be roughly 42.000 times smaller, by surface area alone. You'd think that for a number like that, it would pay to improve your aperture a bit.
Is everyone here assuming that the laser would have zero divergence??? From my experience, if you were gonna shoot down an ICBM with a laser, it would be at long range, and over that kind of range you'd be lucky to have a spot with a diameter of less than about 20-30m diameter. A spinning missile would have very little effect I suspect.
And tracking a missile is trivial. It is currently employed in laser systems which shoot down missiles at very short ranges, i.e. much larger angular velocities, so would certainly not be a problem with an ICBM.
The biggest problem is power and atmospheric power losses, AFAIK.
QUOTE (Alcari+)
Well, it would take exact figures to find out the answer, as well as (most likely) classified information on how such a laser can maintain a beam, what the output is, whether it functions by melting a hole or by overheating the missile, etc etc etc.
Such a laser would not maintain a beam, it would be a pulsed laser, operating in the region of ns pulses.
Such a laser would not maintain a beam, it would be a pulsed laser, operating in the region of ns pulses.
QUOTE
Such a laser would not maintain a beam, it would be a pulsed laser, operating in the region of ns pulses.
Ah right... I forgot to to include the duration of the pulse. Of course if it's so short, you'd have to spin the missile at insane speeds in order for it to have an effect. Still, a reflective mirror seems to be a very cheap countermeasure against such a weapon, unles the output of the laser is allready several orders of magnitude higher than needed.
I have exactly zero experience with chemical lasers, but I asume they are quite capable of projecting an almost perfectly straight beam. So you would only have to deal with atmospheric scattering. A few kilometers isn't that far at the speed of light.
As for divergence, if the "business end" of the beam is a 20 meter diameter spot, wouldn't that be a massive waste of energy? If the spot were, say, 5cm (random guess), the ammount of energy required to reach the same effect would be roughly 42.000 times smaller, by surface area alone. You'd think that for a number like that, it would pay to improve your aperture a bit.
QUOTE (Alcari+Jun 25 2008, 04:01 PM)
Ah right... I forgot to to include the duration of the pulse. Of course if it's so short, you'd have to spin the missile at insane speeds in order for it to have an effect. Still, a reflective mirror seems to be a very cheap countermeasure against such a weapon, unles the output of the laser is allready several orders of magnitude higher than needed.
If the beam is powerful enough to knock a missile out of the sky a reflective mirror won't stand up to much, regardless of its reflectivity.
Since you talk about divergence below, I'll assume you don't mean divergence here. Atmospheric scintillation isn't necessarily a bad thing, it breaks the beam up and you don't get the energy spike in the centre of the beam, but you do end up with small spots of up to 3x the original peak energy, can be quite a handy tool!
Not really sure what you mean by straight beam? Divergence? The path being bent by the atmosphere?
And you'd want to hit your ICBM a bit before it hits a few km away! (Try thousands of km...)
Since you talk about divergence below, I'll assume you don't mean divergence here. Atmospheric scintillation isn't necessarily a bad thing, it breaks the beam up and you don't get the energy spike in the centre of the beam, but you do end up with small spots of up to 3x the original peak energy, can be quite a handy tool!
Not really sure what you mean by straight beam? Divergence? The path being bent by the atmosphere?
And you'd want to hit your ICBM a bit before it hits a few km away! (Try thousands of km...)
As for divergence, if the "business end" of the beam is a 20 meter diameter spot, wouldn't that be a massive waste of energy? If the spot were, say, 5cm (random guess), the ammount of energy required to reach the same effect would be roughly 42.000 times smaller, by surface area alone. You'd think that for a number like that, it would pay to improve your aperture a bit.
Of course it's a waste of energy, but it makes it a lot easier to hit the target.
Let's say a 2m diameter aperture produces a 10m spot at 500km, that's 8m of divergence. If you double the aperture you've got 4m before it even diverges, so even if the divergence is down to 2m, you're only down to a 6m spot!
Tiny spots just ain't practical at large distances.
A lack of complete knowledge has never me stopped me speculating and guessing
But yeah, you're right, several billions of dollars in R&D and dozens of years of work probably reached a much better answer then a week of random guessing on a forum. The answer really is in the details, and those take a lot of knowledge and effort to figure out.
i know next to nothing of how chemical lasers do their job, and equally little of ICBMs, so i'm constantly taking your word for it, but I do know a little about optics (well, a lot actually), so the reflection idea seemed like an obvious guess.
How shiny can you make aluminum? 93%? Can you make the entire missile 93% reflective?
1/(1-.93) = 14.3
If someone, sometime, makes a shiny rocket, we up the laser power by 14x. We're always interested in lasers that are "scalable", meaning, if we want to, we know how to make one 10x more powerful, or 100x more powerful...
Also, from your knowledge of optics, you recognize that reflectivity is usually a function of wavelength. Something that's 93% reflective at one wavelength might be a lot less reflective at another wavelength. We can make lasers that work at different wavelengths where the missile's not shiny.
http://patft.uspto.gov/netacgi/nph-Parser?...ec+AND+elliott)
It's a link to a patent I share with Jan Vetrovec (#7,310,360) on cooling optics used with High-Energy lasers. Gee, I wonder how my name got on that High-Energy Laser Optics patent.
Your guess is way off base. I worked on SDI, I worked on Space Based Laser, and I worked with the architects of ABL.
Alcari's points are spot-on, a "wide-band dielectric HR coating" isn't all that wide-band. If the enemy guesses wrong about the wavelength, that dielectric mirror's reflectivity drops to nil.
Everybody here is talking about IR wavelengths. Long wavelengths make everything look shiny, it's the shorter wavelengths where shiny surfaces start looking rough, and therefore absorptive.
And I wouldn't be so fast to discount "electric lasers", if I were you, and they come in lots of wavelengths, including visible.
Also, google "HELLADS".
The precise diameter of the SBL beam-director (big mirror of the aiming telescope) is/was classified, but let's just say it wouldn't fit in a truck (regardless of whatever kind of truck you pick). The focus size on-target was also classified, but if it was a plate, it'd be hard to put a turkey on. Take the ratios of the areas, and you get orders of magnitude.
SBL was a "project" to demonstrate the *feasibility* of shooting down a target missile with a laser, not a *prototype* of the actual laser they wanted to field. That, too, would've been a lot more powerful than the SBL laser (which was already reported as a "MW-class Hydrogen-Fluoride laser). ABL uses a COIL (Chemical Oxygen-Iodide Laser), and, ironically, it was the company I work for that pioneered the COIL concept.
Anybody here know how green laser pointers work? I'll leave that as a homework assignment for those who are really interested in gaining some insights into this field.
No, if they're reflective at one frequency, they're absorptive at twice that frequency.
Still haven't figured out how green laser pointers work, have you? I suggest you do a google search on how green laser pointers work before responding.
Obviously, you don't know how either Highly-reflective dielectric coatings work or Anti-reflective coatings work.
They're built up alternating layers of dielectric coatings that have slightly different coefficients of refraction. The differences in coefficients means that a slight reflection occurs at each surface. If the surfaces are spaced a half-wavelength apart, then the reflections build up by constructive interference, having traversed a full wavelength through each layer and back, so you get a highly-reflective coating - one of those 99.995% reflective mirrors, but only at that wavelength. If the wavelength is twice as long, then the layers are 1/4-wavelength thick, and when they reflect, they're 180degrees out-of-phase with the incident wave, and you have an antireflective coating (which is 99.995% absorptive) at that wavelength.
Green laser pointers aren't green lasers, they start out as IR lasers and use a "frequency-doubler" to halve their wavelength/double their frequency, transforming some of the power into green light, and the rest into heat in the doubler medium. When you do that with a powerful laser, you need to remove that waste heat by some means. Patent # 7,310,360, issued to Boeing (the prime contractor for both AirBorne Laser and the Space-Based Laser/Integrated Flight Experiment (SBL/IFX), illustrates several means of cooling optical media, including laser media and frequency-doubler media.
Another way of having your name on a patent is by being the guy who came up with the idea.
Visit my website, read, and learn:
http://hometown.aol.com/aliyat/WmCarterElliott.html
Which you can access via:
http://www.thethousand.com/memberpages.html
(You might want to take note of the entrance requirements for the ISPE before responding.)
BTW, aside from trying to bluff your way through this entire thread, you've accused me of dishonesty. You owe me an apology.
In "laser cannon warfare", we're using megawatt-class lasers to attack missiles. Missiles aren't made from transmissive materials, they're generally made from aluminum. I've acknowledged that aluminum can be polished to 93% reflectivity, but I've said that 93% isn't enough for the missile to survive. That's where the 99.999% reflective coatings got mentioned. I said that they'd be ineffective at wavelengths other than that one wavelength where the coating would be 99.999% reflective, and pointed out that the same coating would be worse than nothing at other wavelengths, and pointed out that changing the wavelength of a laser is done routinely in, for example, green laser pointers (which use IR lasers as pumps for non-linear optical media which changes the wavelength from IR to green).
http://www.repairfaq.org/sam/laserpic/glpdpics.htm
Please note in the above link that the laser used to generate a green laser is at 808nm, while the green laser is at 532nm. It isn't merely doubled in frequency, there's an intermediate step that changes the 808nm to 1064nm, then the doubler changes it to half of 1064nm (532nm). This was what I'd strongly recommended that Enthalpy look up on his own before continuing the argument. He apparently didn't bother do a five-minute google search, as I'd advised.
I don't mind when people are factually incorrect, and I don't get personal when I correct a mistake, but I do take insults personally, and calling me a liar because I know more about optics is an insult.
If the beam is powerful enough to knock a missile out of the sky a reflective mirror won't stand up to much, regardless of its reflectivity.
QUOTE
I have exactly zero experience with chemical lasers, but I asume they are quite capable of projecting an almost perfectly straight beam. So you would only have to deal with atmospheric scattering. A few kilometers isn't that far at the speed of light.
Since you talk about divergence below, I'll assume you don't mean divergence here. Atmospheric scintillation isn't necessarily a bad thing, it breaks the beam up and you don't get the energy spike in the centre of the beam, but you do end up with small spots of up to 3x the original peak energy, can be quite a handy tool!
Not really sure what you mean by straight beam? Divergence? The path being bent by the atmosphere?
And you'd want to hit your ICBM a bit before it hits a few km away! (Try thousands of km...)
QUOTE (->
| QUOTE |
| I have exactly zero experience with chemical lasers, but I asume they are quite capable of projecting an almost perfectly straight beam. So you would only have to deal with atmospheric scattering. A few kilometers isn't that far at the speed of light. |
Since you talk about divergence below, I'll assume you don't mean divergence here. Atmospheric scintillation isn't necessarily a bad thing, it breaks the beam up and you don't get the energy spike in the centre of the beam, but you do end up with small spots of up to 3x the original peak energy, can be quite a handy tool!
Not really sure what you mean by straight beam? Divergence? The path being bent by the atmosphere?
And you'd want to hit your ICBM a bit before it hits a few km away! (Try thousands of km...)
As for divergence, if the "business end" of the beam is a 20 meter diameter spot, wouldn't that be a massive waste of energy? If the spot were, say, 5cm (random guess), the ammount of energy required to reach the same effect would be roughly 42.000 times smaller, by surface area alone. You'd think that for a number like that, it would pay to improve your aperture a bit.
Of course it's a waste of energy, but it makes it a lot easier to hit the target.
Let's say a 2m diameter aperture produces a 10m spot at 500km, that's 8m of divergence. If you double the aperture you've got 4m before it even diverges, so even if the divergence is down to 2m, you're only down to a 6m spot!
Tiny spots just ain't practical at large distances.
I have to keep this brief for several reasons, but overall, Alcari's instincts seem to be pretty good.
The means by which lasers actually destroy missiles is rather closely-held. We don't talk about it much, as that'd be handing a blueprint to our enemies to follow.
Beams diverge inversely proportional to the diameter of their beam-director (telescope) aperture. Bigger mirrors make smaller spots. Half the size of a spot, and you've increased the power-density by 4x (half in the X-direction, half in the Y-direction). At some point, you can't build a bigger mirror. The same divergence equation is inversely-proportional to wavelength, also, so if you can halve the wavelength of the laser, with the same big mirror, you've increased the power density by a factor of 4x.
You can see how the trends go from there.
Spinning a missile *shouldn't* affect its accuracy, in theory, but in practice, it does. It throws in big sinewave accelerations into the accelerometers that have to be subtracted in order to measure the *actual* acceleration of the missile, and most accelerometers and gyroscopes have second-order nonlinearities that are hard to predict and harder to cancel out. It's these "Inertial Measurement Units" that determine how accurate a missile is, and even with nukes, if you're going after hard targets, you need the accuracy, because the targets are buried in underground silos. Miss by a little, you don't destroy the missile in the silo. Spin the missile, and the IMU output gets inaccurate and you miss the silo by too much, you've just spilled the silo-guys' coffee and made 'em mad.
And there are always essential parts of a missile that you can't make shiny.
A lot of people smarter than me have worked these on these ideas a long, long time. Some answers aren't as easy to figure out as the points I've made here. I can't talk about those. Midwestern gets that, and I appreciate it.
The means by which lasers actually destroy missiles is rather closely-held. We don't talk about it much, as that'd be handing a blueprint to our enemies to follow.
Beams diverge inversely proportional to the diameter of their beam-director (telescope) aperture. Bigger mirrors make smaller spots. Half the size of a spot, and you've increased the power-density by 4x (half in the X-direction, half in the Y-direction). At some point, you can't build a bigger mirror. The same divergence equation is inversely-proportional to wavelength, also, so if you can halve the wavelength of the laser, with the same big mirror, you've increased the power density by a factor of 4x.
You can see how the trends go from there.
Spinning a missile *shouldn't* affect its accuracy, in theory, but in practice, it does. It throws in big sinewave accelerations into the accelerometers that have to be subtracted in order to measure the *actual* acceleration of the missile, and most accelerometers and gyroscopes have second-order nonlinearities that are hard to predict and harder to cancel out. It's these "Inertial Measurement Units" that determine how accurate a missile is, and even with nukes, if you're going after hard targets, you need the accuracy, because the targets are buried in underground silos. Miss by a little, you don't destroy the missile in the silo. Spin the missile, and the IMU output gets inaccurate and you miss the silo by too much, you've just spilled the silo-guys' coffee and made 'em mad.
And there are always essential parts of a missile that you can't make shiny.
A lot of people smarter than me have worked these on these ideas a long, long time. Some answers aren't as easy to figure out as the points I've made here. I can't talk about those. Midwestern gets that, and I appreciate it.
QUOTE
A lot of people smarter than me have worked these on these ideas a long, long time. Some answers aren't as easy to figure out as the points I've made here. I can't talk about those. Midwestern gets that, and I appreciate it.
A lack of complete knowledge has never me stopped me speculating and guessing
But yeah, you're right, several billions of dollars in R&D and dozens of years of work probably reached a much better answer then a week of random guessing on a forum. The answer really is in the details, and those take a lot of knowledge and effort to figure out.
i know next to nothing of how chemical lasers do their job, and equally little of ICBMs, so i'm constantly taking your word for it, but I do know a little about optics (well, a lot actually), so the reflection idea seemed like an obvious guess.
QUOTE
the reflection idea seemed like an obvious guess.
How shiny can you make aluminum? 93%? Can you make the entire missile 93% reflective?
1/(1-.93) = 14.3
If someone, sometime, makes a shiny rocket, we up the laser power by 14x. We're always interested in lasers that are "scalable", meaning, if we want to, we know how to make one 10x more powerful, or 100x more powerful...
Also, from your knowledge of optics, you recognize that reflectivity is usually a function of wavelength. Something that's 93% reflective at one wavelength might be a lot less reflective at another wavelength. We can make lasers that work at different wavelengths where the missile's not shiny.
I don't have the tables handy at the moment, but I believe aluminum goes to about 90% in the infrared range, gold coating to 95-96%. At least, under clean-room circumstances, which I don't think apply after you ignite several thousand pounds of rocket fuel below it.
Of course, if you wanted, you could cover the whole thing with more advanced dielectric mirrors, which can reach up to 99.995% in optimal conditions, but that might be rather expensive for a whole missile.
Ahh, that I did not know. I thought it required building a totally new laser, or at least a lot of switching out parts. Not turning the proverbial dial to the right. If making a laser ten times more powerful doesn't cost that much more, then I guess the whole idea that reflective missiles might be "to expensive" to shoot down, is a bust.
Again, the only thing I know about chemical lasers was the theory in high-school physics, which is quite a while ago. We don't really use them in astronomy, unlike solid-state lasers.
Well, I guess I can say goodbye to my cheap anti-laser system, not that I had illusion that it could work, but it was a great discussion.
Of course, if you wanted, you could cover the whole thing with more advanced dielectric mirrors, which can reach up to 99.995% in optimal conditions, but that might be rather expensive for a whole missile.
QUOTE
If someone, sometime, makes a shiny rocket, we up the laser power by 14x. We're always interested in lasers that are "scalable", meaning, if we want to, we know how to make one 10x more powerful, or 100x more powerful...
Ahh, that I did not know. I thought it required building a totally new laser, or at least a lot of switching out parts. Not turning the proverbial dial to the right. If making a laser ten times more powerful doesn't cost that much more, then I guess the whole idea that reflective missiles might be "to expensive" to shoot down, is a bust.
Again, the only thing I know about chemical lasers was the theory in high-school physics, which is quite a while ago. We don't really use them in astronomy, unlike solid-state lasers.
Well, I guess I can say goodbye to my cheap anti-laser system, not that I had illusion that it could work, but it was a great discussion.
Hi there,
you don't need to guess that much about these lasers, as much data is published.
Chemical lasers have no room for choosing the wavelength, as this is determined by the chemical reaction, and very few reactions (= exactly one up to now) are usable.
Reflectivity is far better than 93% for good metals, and a dielectric mirror is cheap, especially since this one wouldn't need optic quality (no focussing).
Emitted power isn't easily upscalable, as it has already been upscaled. One harsh limit is the weapon's mirror that must withstand the power, which is about as concentrated there as on the target. Another is the laser's size: already a full Jumbojet.
The atmosphere is less critical than you expect, as the laser is already at 10km altitude (if not 300km) and the target out of the atmosphere. This avoids clouds. And at some power density, the atmosphere actually concentrates the ray instead of scattering it, because ionization reduces the phase velocity. But I believe this applies to pulsed lasers, not to chemical lasers whose peak power is lower.
Gyroscopes are abandoned. Gyrolasers and Sagnac gyros are insensitive to added rotations.
you don't need to guess that much about these lasers, as much data is published.
Chemical lasers have no room for choosing the wavelength, as this is determined by the chemical reaction, and very few reactions (= exactly one up to now) are usable.
Reflectivity is far better than 93% for good metals, and a dielectric mirror is cheap, especially since this one wouldn't need optic quality (no focussing).
Emitted power isn't easily upscalable, as it has already been upscaled. One harsh limit is the weapon's mirror that must withstand the power, which is about as concentrated there as on the target. Another is the laser's size: already a full Jumbojet.
The atmosphere is less critical than you expect, as the laser is already at 10km altitude (if not 300km) and the target out of the atmosphere. This avoids clouds. And at some power density, the atmosphere actually concentrates the ray instead of scattering it, because ionization reduces the phase velocity. But I believe this applies to pulsed lasers, not to chemical lasers whose peak power is lower.
Gyroscopes are abandoned. Gyrolasers and Sagnac gyros are insensitive to added rotations.
Scalable doesn't necessarily mean cheap, only that it can be done, and we know how.
There are more than one chemical lasers, and HE lasers aren't necessarily limited to chemical lasers.
Dielectric coatings can be 99.995% reflective, but only at one wavelength (and to a beam normal to the surface). At other wavelengths or other incident angles, those dielectric mirrors become absorptive.
The whole point of having a big mirror for the beam director is to increase the flux density on the target to greater than it is on the big mirror. The flux densities *aren't* the same, they're different by orders of magnitude.
A lot of the basic physics is already "out there", as Enthalpy pointed out, but a lot of the techniques for getting around the sticky issues *aren't*, and I think it's wise to keep it that way.
There are more than one chemical lasers, and HE lasers aren't necessarily limited to chemical lasers.
Dielectric coatings can be 99.995% reflective, but only at one wavelength (and to a beam normal to the surface). At other wavelengths or other incident angles, those dielectric mirrors become absorptive.
The whole point of having a big mirror for the beam director is to increase the flux density on the target to greater than it is on the big mirror. The flux densities *aren't* the same, they're different by orders of magnitude.
A lot of the basic physics is already "out there", as Enthalpy pointed out, but a lot of the techniques for getting around the sticky issues *aren't*, and I think it's wise to keep it that way.
In the multimegawatt range over seconds duration, one has little choice. A few other chemical reactions are available (but deuterium fluoride would be worse for gold's reflectivity), as well as liquid lasers. The electric power would be available on a Jumbo, but the laser not really. Electrically pumped CO2 has this power, but at a bad wavelength.
Some infos simply here
http://en.wikipedia.org/wiki/Airborne_Laser
http://en.wikipedia.org/wiki/Chemical_oxygen_iodine_laser
little there www.boeing.com/defense-space/military/ab
which is more than enough to compute the ideally attainable focus size.
I would expect this ideal size to have been indeed attained - with a huge effort.
Dielectric mirrors can be and are made wideband, of course. Routinely done. And for many incidences, of course as well. Sure, it's more complicated than what stands in textbooks.
At the 1.315 µm of the chemical iodine laser, the reflectivity of clean gold is 0.992 and aluminium 0.97.
At the 3.8 µm of the chemical deuterium iodine laser, the reflectivity of clean gold is 0.995 and aluminium 0.984.
Reflective coating suggested here:
http://en.wikipedia.org/wiki/Tactical_High_Energy_Laser
Power density: as the power is the same at the mirror and the target in the best possible case, it reduces to comparing surfaces. Make a short computation and see that, at the announced 300km, there aren't orders of magnitude between the mirror and the remote spot size.
Some infos simply here
http://en.wikipedia.org/wiki/Airborne_Laser
http://en.wikipedia.org/wiki/Chemical_oxygen_iodine_laser
little there www.boeing.com/defense-space/military/ab
which is more than enough to compute the ideally attainable focus size.
I would expect this ideal size to have been indeed attained - with a huge effort.
Dielectric mirrors can be and are made wideband, of course. Routinely done. And for many incidences, of course as well. Sure, it's more complicated than what stands in textbooks.
At the 1.315 µm of the chemical iodine laser, the reflectivity of clean gold is 0.992 and aluminium 0.97.
At the 3.8 µm of the chemical deuterium iodine laser, the reflectivity of clean gold is 0.995 and aluminium 0.984.
Reflective coating suggested here:
http://en.wikipedia.org/wiki/Tactical_High_Energy_Laser
Power density: as the power is the same at the mirror and the target in the best possible case, it reduces to comparing surfaces. Make a short computation and see that, at the announced 300km, there aren't orders of magnitude between the mirror and the remote spot size.
Thanks for looking up the numbers Enthalpy. Keep in mind those are theoretical maximum values under laboratory conditions. I assume a missile silo isn't exactly a clean-room. Still, a 97 - 98 % reflection should be achievable for an acceptable cost.
Now, I can only assume any strategic missile defense system would already build to take this into account, or the designers would be immense fools.
What I would do, in my very limited experience, if countermeasures are already taken into account, is build a laser that is capable of knocking a >99% reflective missile with ablative coating and whatever else works, and make it fire in two ways.
First, give the cheap, short, low power pulse that will knock out an unprotected target. If the target is still there, switch to Death-star mode and try again. Assuming there's no saturation bombardment, such a tactic would work right?
----Concerning Dielectric mirrors.
Yes, dielectric coating CAN be wide-band, but "Wide" is a relative concept. A wide-band mirror reflects optimally at a wavelength of 20 nm wide at best.
As for reflection angle, you're stuck with half an arcminute (1 MOA = 290µrad) at best, a few arcseconds at worst. Seeing how missiles are round, you always hit part of it at a very large angle, where the coating will be useless. Less then useless in fact, as the coating itself is quite absorbing.
However, dielectric mirrors are out anyway, seeing how it would cost far to much. DE mirrors are made by thin-film deposition, so whether or not it needs to be focused doesn't really matter. We have a flat, hubcap sized DE mirror at the "old-fashioned" observatory, which was more expensive than my house. Now, I don't know what an ICBM, or a delivery vehicle costs, but I don't think it's worth it to coat it in DE mirrors.
Now, I can only assume any strategic missile defense system would already build to take this into account, or the designers would be immense fools.
What I would do, in my very limited experience, if countermeasures are already taken into account, is build a laser that is capable of knocking a >99% reflective missile with ablative coating and whatever else works, and make it fire in two ways.
First, give the cheap, short, low power pulse that will knock out an unprotected target. If the target is still there, switch to Death-star mode and try again. Assuming there's no saturation bombardment, such a tactic would work right?
----Concerning Dielectric mirrors.
Yes, dielectric coating CAN be wide-band, but "Wide" is a relative concept. A wide-band mirror reflects optimally at a wavelength of 20 nm wide at best.
As for reflection angle, you're stuck with half an arcminute (1 MOA = 290µrad) at best, a few arcseconds at worst. Seeing how missiles are round, you always hit part of it at a very large angle, where the coating will be useless. Less then useless in fact, as the coating itself is quite absorbing.
However, dielectric mirrors are out anyway, seeing how it would cost far to much. DE mirrors are made by thin-film deposition, so whether or not it needs to be focused doesn't really matter. We have a flat, hubcap sized DE mirror at the "old-fashioned" observatory, which was more expensive than my house. Now, I don't know what an ICBM, or a delivery vehicle costs, but I don't think it's worth it to coat it in DE mirrors.
Forget about the price of telescope mirrors. They must have the curvature precision of a telescope, which a protective mirror doesn't.
You figures about bandpass and angle are old-fashioned to say the least. And unconsistent between bandpass and angle anyway, so I would say: simply invented.
Coatings are not absorbing but transparent when they don't reflect light.
No relationship between thin-film and focussing. Your arguments shouldn't resemble WCElliott's ones.
Anyway, I would use a metal coating. And yes, I count with the maximum value (these are measured, not theoretical), because the laser hit cleans the metal from dirt. So 0.99 at 1.3µm, yes.
Price of ICBM: what about >100,000,000,000 usd for 3000 pieces?
What you would do is take countermeasures into account... Only if this were possible! Laser weapons are at the limit of technical possibilities at 300km distance without countermeasures and hence are defeated by missile hardening, which doesn't even look difficult. This is maybe the one fact sellers and buyers of such weapons want to keep secret.
My guess: WCElliott did not work on laser weapons neither (and once again), as the vague figures he provided were radically false, and he conceiled his ignorance by asserting public data as secret. Hi, Alcari.
You figures about bandpass and angle are old-fashioned to say the least. And unconsistent between bandpass and angle anyway, so I would say: simply invented.
Coatings are not absorbing but transparent when they don't reflect light.
No relationship between thin-film and focussing. Your arguments shouldn't resemble WCElliott's ones.
Anyway, I would use a metal coating. And yes, I count with the maximum value (these are measured, not theoretical), because the laser hit cleans the metal from dirt. So 0.99 at 1.3µm, yes.
Price of ICBM: what about >100,000,000,000 usd for 3000 pieces?
What you would do is take countermeasures into account... Only if this were possible! Laser weapons are at the limit of technical possibilities at 300km distance without countermeasures and hence are defeated by missile hardening, which doesn't even look difficult. This is maybe the one fact sellers and buyers of such weapons want to keep secret.
My guess: WCElliott did not work on laser weapons neither (and once again), as the vague figures he provided were radically false, and he conceiled his ignorance by asserting public data as secret. Hi, Alcari.
QUOTE
My guess: WCElliott did not work on laser weapons neither (and once again), as the vague figures he provided were radically false, and he conceiled his ignorance by asserting public data as secret. Hi, Alcari.
http://patft.uspto.gov/netacgi/nph-Parser?...ec+AND+elliott)
It's a link to a patent I share with Jan Vetrovec (#7,310,360) on cooling optics used with High-Energy lasers. Gee, I wonder how my name got on that High-Energy Laser Optics patent.
Your guess is way off base. I worked on SDI, I worked on Space Based Laser, and I worked with the architects of ABL.
Alcari's points are spot-on, a "wide-band dielectric HR coating" isn't all that wide-band. If the enemy guesses wrong about the wavelength, that dielectric mirror's reflectivity drops to nil.
Everybody here is talking about IR wavelengths. Long wavelengths make everything look shiny, it's the shorter wavelengths where shiny surfaces start looking rough, and therefore absorptive.
And I wouldn't be so fast to discount "electric lasers", if I were you, and they come in lots of wavelengths, including visible.
Also, google "HELLADS".
The precise diameter of the SBL beam-director (big mirror of the aiming telescope) is/was classified, but let's just say it wouldn't fit in a truck (regardless of whatever kind of truck you pick). The focus size on-target was also classified, but if it was a plate, it'd be hard to put a turkey on. Take the ratios of the areas, and you get orders of magnitude.
SBL was a "project" to demonstrate the *feasibility* of shooting down a target missile with a laser, not a *prototype* of the actual laser they wanted to field. That, too, would've been a lot more powerful than the SBL laser (which was already reported as a "MW-class Hydrogen-Fluoride laser). ABL uses a COIL (Chemical Oxygen-Iodide Laser), and, ironically, it was the company I work for that pioneered the COIL concept.
Anybody here know how green laser pointers work? I'll leave that as a homework assignment for those who are really interested in gaining some insights into this field.
Dielectric mirrors can of course be made wide band. And as only two or three wavelength give the necessary output power for a weapon, it's completely obvious to superimpose mirrors tuned to each wavelength, as a detuned dielectric mirror is tranparent and not absorptive.
You suggest specular reflectivity, but diffuse reflectivity is just as good to protect against a weapon laser, and this has nothing to do with roughness. This is strictly a matter of electron-crystal interaction. Basic optics.
We talk about IR because powerful lasers are in IR.
Electric pumping: only if one gets a significant mean power. This is the basic reason why all existing weapon laser are chemical and thus infrared.
You suggest specular reflectivity, but diffuse reflectivity is just as good to protect against a weapon laser, and this has nothing to do with roughness. This is strictly a matter of electron-crystal interaction. Basic optics.
We talk about IR because powerful lasers are in IR.
Electric pumping: only if one gets a significant mean power. This is the basic reason why all existing weapon laser are chemical and thus infrared.
QUOTE
a detuned dielectric mirror is tranparent and not absorptive.
No, if they're reflective at one frequency, they're absorptive at twice that frequency.
Still haven't figured out how green laser pointers work, have you? I suggest you do a google search on how green laser pointers work before responding.
False again. Basic optics again.
A dielectric mirror reflective at one frequency is transparent at twice that frequency, not absorptive. Obviously, you ignore the difference between both notions. Bad beginning for a nontrivial topic as laser weapons. Find a read an elementary optics book.
Absorptive materials can't make a dielectric mirror, which absolutely needs low-loss materials.
-------------
A few ways to have one's name on a patent:
- Work at a company who contracts a university to make research. The contract stipulates that inventions belong to the company. The university's researcher makes an invention, you have your name on the patent.
- Be the chief of an inventor.
- Be the colleague of an inventor.
- Have the same name as an inventor. Allegate you're the inventor.
--------------
So you've already googled "laser pointer"? That's a bit short to explain how a weapon laser works. Power scalability for instance is easier for pointers than for weapons. Divergence as well.
A dielectric mirror reflective at one frequency is transparent at twice that frequency, not absorptive. Obviously, you ignore the difference between both notions. Bad beginning for a nontrivial topic as laser weapons. Find a read an elementary optics book.
Absorptive materials can't make a dielectric mirror, which absolutely needs low-loss materials.
-------------
A few ways to have one's name on a patent:
- Work at a company who contracts a university to make research. The contract stipulates that inventions belong to the company. The university's researcher makes an invention, you have your name on the patent.
- Be the chief of an inventor.
- Be the colleague of an inventor.
- Have the same name as an inventor. Allegate you're the inventor.
--------------
So you've already googled "laser pointer"? That's a bit short to explain how a weapon laser works. Power scalability for instance is easier for pointers than for weapons. Divergence as well.
QUOTE
A dielectric mirror reflective at one frequency is transparent at twice that frequency, not absorptive. Obviously, you ignore the difference between both notions.
Obviously, you don't know how either Highly-reflective dielectric coatings work or Anti-reflective coatings work.
They're built up alternating layers of dielectric coatings that have slightly different coefficients of refraction. The differences in coefficients means that a slight reflection occurs at each surface. If the surfaces are spaced a half-wavelength apart, then the reflections build up by constructive interference, having traversed a full wavelength through each layer and back, so you get a highly-reflective coating - one of those 99.995% reflective mirrors, but only at that wavelength. If the wavelength is twice as long, then the layers are 1/4-wavelength thick, and when they reflect, they're 180degrees out-of-phase with the incident wave, and you have an antireflective coating (which is 99.995% absorptive) at that wavelength.
Green laser pointers aren't green lasers, they start out as IR lasers and use a "frequency-doubler" to halve their wavelength/double their frequency, transforming some of the power into green light, and the rest into heat in the doubler medium. When you do that with a powerful laser, you need to remove that waste heat by some means. Patent # 7,310,360, issued to Boeing (the prime contractor for both AirBorne Laser and the Space-Based Laser/Integrated Flight Experiment (SBL/IFX), illustrates several means of cooling optical media, including laser media and frequency-doubler media.
Another way of having your name on a patent is by being the guy who came up with the idea.
Visit my website, read, and learn:
http://hometown.aol.com/aliyat/WmCarterElliott.html
Which you can access via:
http://www.thethousand.com/memberpages.html
(You might want to take note of the entrance requirements for the ISPE before responding.)
BTW, aside from trying to bluff your way through this entire thread, you've accused me of dishonesty. You owe me an apology.
WCElliott, you look more and more stupid each time you show you ignorance.
1/4 wavelength thickness may make an antireflective coating, which then transmits light and doesn't absorb it. This is the purpose of antireflective coating: transmit light.
You have clearly shown you know nothing about optics. Not the most basic notions.
So I repeat: get an elementary book, read it and try to understand, and you may then write less ridiculous posts.
1/4 wavelength thickness may make an antireflective coating, which then transmits light and doesn't absorb it. This is the purpose of antireflective coating: transmit light.
You have clearly shown you know nothing about optics. Not the most basic notions.
So I repeat: get an elementary book, read it and try to understand, and you may then write less ridiculous posts.
Enthalpy - It isn't the basics of optics we're discussing, but more advanced optics that *you* clearly don't understand.
I did about half my Masters' Degree in the field of optics, including lasers and holography.
I'm waiting to hear from DARPA on whether or not they're going to fund a laser radar satellite payload of my design.
I worked on SBL for three years, and SDI for three years in the mid-80's as a Senior Staff Scientist for SAIC.
You haven't gotten a single point correct yet.
Get wise, you've lost this "debate". You aren't even in the same league.
I did about half my Masters' Degree in the field of optics, including lasers and holography.
I'm waiting to hear from DARPA on whether or not they're going to fund a laser radar satellite payload of my design.
I worked on SBL for three years, and SDI for three years in the mid-80's as a Senior Staff Scientist for SAIC.
You haven't gotten a single point correct yet.
Get wise, you've lost this "debate". You aren't even in the same league.
QUOTE (wcelliott+Jul 10 2008, 03:36 AM)
I did about half my Masters' Degree in the field of optics, including lasers and holography.
Laser cutters are like analogous to knives. Sharpness/thinness area v psi.
A laser classroom laser pointer that uses 3 watch batteries and the size of a 38 long rifle cartridge could possibly cut down a tree with a slash if the beam was narrowed from 2mm to a smaller than micron area beam at the same power. My question is with respect to your education in optics and lasers, given 3 watch batteries how narrow would the beam have to be to make that laser a lethal cutter?
I'm asking because considerable advances have been made with the development and miniaturization of tasers leading to the X-Rep Taser
http://tech-gadget-id.blogspot.com/2007/07...ep-shotgun.html
Laser cutters are like analogous to knives. Sharpness/thinness area v psi.
A laser classroom laser pointer that uses 3 watch batteries and the size of a 38 long rifle cartridge could possibly cut down a tree with a slash if the beam was narrowed from 2mm to a smaller than micron area beam at the same power. My question is with respect to your education in optics and lasers, given 3 watch batteries how narrow would the beam have to be to make that laser a lethal cutter?
I'm asking because considerable advances have been made with the development and miniaturization of tasers leading to the X-Rep Taser
http://tech-gadget-id.blogspot.com/2007/07...ep-shotgun.html
The power in the beam will be considerably less than the power supplied by the three watch batteries, so even if the beam quality of the laser pointer were good enough for you to make a "burning laser" out of it with optics, it'd take lots of watch batteries and a long, long time to burn through a tree.
I'd recommend a chainsaw.
I'd recommend a chainsaw.
WCElliott, I guess reading a basic optics book (they do explain dielectric mirrors and antireflective coatings) would be too much of an effort to you, but there is another solution.
Find a dictionary. Read the entries "transparent" and "absorptive". This should do the trick.
If this dictionary is very complete, it may tell you also the difference between specular and diffuse reflection, another basic mistake you made in the same post.
A laser pointer uses a laser diode (and sometimes a frequency multiplier) whose efficiency isn't that bad. Quantum efficiency is in the order of 1, the best among all lasers; power efficiency can be around 1/3. Still, not the faintest hope to cut a tree.
As for the apologies you suggested, WCElliott: if you enjoy reading some, you should write them by yourself.
Just a word for people who understand a bit of optics: materials used for dielectric mirrors must have very low losses, because such mirrors contain EM-fields in many layers and though don't waste power, as their high reflectivity tells. So outside their band, their low losses make them very transparent.
Find a dictionary. Read the entries "transparent" and "absorptive". This should do the trick.
If this dictionary is very complete, it may tell you also the difference between specular and diffuse reflection, another basic mistake you made in the same post.
A laser pointer uses a laser diode (and sometimes a frequency multiplier) whose efficiency isn't that bad. Quantum efficiency is in the order of 1, the best among all lasers; power efficiency can be around 1/3. Still, not the faintest hope to cut a tree.
As for the apologies you suggested, WCElliott: if you enjoy reading some, you should write them by yourself.
Just a word for people who understand a bit of optics: materials used for dielectric mirrors must have very low losses, because such mirrors contain EM-fields in many layers and though don't waste power, as their high reflectivity tells. So outside their band, their low losses make them very transparent.
Enthalpy -
Apparently you're having reading comprehension problems. Maxwords asked about using a laser pointer to cut down a tree, and I'm the one who told him it was impractical, if not infeasible.
Also, you've missed the part where I said I did half my MS in optics, including lasers and holograms. So the "Basic Optics" book is in the garage, under the "Advanced Optics" book, which deals with dielectric materials and non-linear optics (like frequency-doublers).
You still don't understand that the "absorption" of a dielectric mirror has nothing to do with the absorptivity of the materials, but that the same principle that makes a dielectric mirror reflective at one wavelength makes it absorptive at other wavelengths. Until you understand that point, we aren't on the same playing field.
The links I provided support my positions, including that I'm the same William C. Elliott who's listed as co-inventor of Patent# 7,310,360, which deals specifically with means of cooling high-energy laser optics. You basically asserted I'm a liar, and I don't appreciate that insult, and you don't have the personal integrity to admit that you were wrong when you accused me of lying.
You still owe me an apology for that.
You apparently didn't bother following the ISPE link to find my homepage listed on the member's list, and you didn't bother looking up the entrance requirements for ISPE. ISPE is similar to Mensa, except the entrance requirements are 20x harder to get in. You need to provide proof that your IQ is in the top 0.1%-ile (one in a thousand are qualified).
Nothing you've said about optics shows you have the first clue as to what you're talking about.
Apparently you're having reading comprehension problems. Maxwords asked about using a laser pointer to cut down a tree, and I'm the one who told him it was impractical, if not infeasible.
Also, you've missed the part where I said I did half my MS in optics, including lasers and holograms. So the "Basic Optics" book is in the garage, under the "Advanced Optics" book, which deals with dielectric materials and non-linear optics (like frequency-doublers).
You still don't understand that the "absorption" of a dielectric mirror has nothing to do with the absorptivity of the materials, but that the same principle that makes a dielectric mirror reflective at one wavelength makes it absorptive at other wavelengths. Until you understand that point, we aren't on the same playing field.
The links I provided support my positions, including that I'm the same William C. Elliott who's listed as co-inventor of Patent# 7,310,360, which deals specifically with means of cooling high-energy laser optics. You basically asserted I'm a liar, and I don't appreciate that insult, and you don't have the personal integrity to admit that you were wrong when you accused me of lying.
You still owe me an apology for that.
You apparently didn't bother following the ISPE link to find my homepage listed on the member's list, and you didn't bother looking up the entrance requirements for ISPE. ISPE is similar to Mensa, except the entrance requirements are 20x harder to get in. You need to provide proof that your IQ is in the top 0.1%-ile (one in a thousand are qualified).
Nothing you've said about optics shows you have the first clue as to what you're talking about.
WCElliott, you can't make the difference between absorb and transmit.
So if you can't read a basic optics book, try a dictionnary.
Though a dictionnary won't tell you a laser diode has a good efficiency. But that's a secondary matter, as few people will notice this mistake when you try to appear as a knowledgeable person for optics.
So if you can't read a basic optics book, try a dictionnary.
Though a dictionnary won't tell you a laser diode has a good efficiency. But that's a secondary matter, as few people will notice this mistake when you try to appear as a knowledgeable person for optics.
A couple weeks ago, I was introduced at a meeting with a new customer as "Our laser guy".
Dielectric mirrors don't work the way you think they do (i.e., by magic). Apparently, your "Basic Optics" book doesn't cover how they work. I explained it before, but you didn't get it.
You should go buy a book on "Advanced Optics" and read how they work.
I've already provided plenty of evidence that I'm the guy with the patent on high-energy laser components. Your position since then shows you have no interest in the truth.
Dielectric mirrors don't work the way you think they do (i.e., by magic). Apparently, your "Basic Optics" book doesn't cover how they work. I explained it before, but you didn't get it.
You should go buy a book on "Advanced Optics" and read how they work.
I've already provided plenty of evidence that I'm the guy with the patent on high-energy laser components. Your position since then shows you have no interest in the truth.
QUOTE (wcelliott+Jul 19 2008, 02:35 AM)
Dielectric mirrors don't work the way you think they do (i.e., by magic). Apparently, your "Basic Optics" book doesn't cover how they work. I explained it before, but you didn't get it.
WC, could you exlain it again to a bystander please?
When light of double the design frequency hits the dielectric, and the reflections cancel, what 'absorbs' the light? The layers are by definition individually very transmissive, no? So it can't be them. And I know from the fact that energy can't be destroyed that light waves 180deg out of phase can't just make the energy 'disappear', so where does it go?
I'm struggling to understand what absorbs the light.
On the other hand, if it is all transmitted, how does the small amount of light which 'should' be reflected by the first layer know to carry on through for complete transmission instead?!?! (I think QED, The Strange Theory of Light and Matter, Richard Feynman might help explain that one!)
Whatever the outcome, this seems like it could be an amicable argument which is debated until all understand the same explanation, no need for it to descend any further, is there?
WC, could you exlain it again to a bystander please?
When light of double the design frequency hits the dielectric, and the reflections cancel, what 'absorbs' the light? The layers are by definition individually very transmissive, no? So it can't be them. And I know from the fact that energy can't be destroyed that light waves 180deg out of phase can't just make the energy 'disappear', so where does it go?
I'm struggling to understand what absorbs the light.
On the other hand, if it is all transmitted, how does the small amount of light which 'should' be reflected by the first layer know to carry on through for complete transmission instead?!?! (I think QED, The Strange Theory of Light and Matter, Richard Feynman might help explain that one!)
Whatever the outcome, this seems like it could be an amicable argument which is debated until all understand the same explanation, no need for it to descend any further, is there?
What happens when a dielectric coating is hit with too much power is that an electric field is generated which exceeds the "dielectric breakdown limit" which blows the layers apart, leaving a scorched substrate. The excess power doesn't disappear, it creates a plasma within the dielectric coating.
From the top:
From the Basic Optics book, look for what happens when light traverses a boundary between two clear substances which have different indices of refraction: the amount of light reflected is proportional to the ratio of the different refractive indices. Think of water in an aquarium, you look in and you get a strong reflection off the glass from the water-side, especially.
The coatings applied to optical surfaces are like that, but they use one other trick. They carefully tailor the thickness of the layers applied. If they want an antireflective coating at a certain wavelength of light, then they make the layer one-quarter wavelength thick. That means that the reflection from the inner surface ends up traversing that layer twice, making it one-half a wavelength out of phase with the reflection from the front surface. (If it's a one-layer thick antireflective coating, they choose a material that's clear at the wavelength desired to transmit, but also that it has an index of refraction that's the harmonic mean of the air and the glass (or whatever the substrate is), so that the two reflections, from the front surface (air-coating) is the same strength as the back surface reflection (coating-substrate). These are what's on camera lenses, and they work nicely over the visible range of light. They don't work in IR at all, though (something that the Ghost Hunters need to learn), because the longer wavelengths make that "1/4-wavelength-thick" coating less than a quarter-wavelenght thick, and so the reflections from the two surfaces don't cancel each other out as designed. They're too close together, so they tend to add in-phase, almost like there isn't an AR coating on it at all.
In a reflective coating, it's the same principle. Make the layers of two (or more) materials that are transmissive at the design-to wavelength, but of intermediate (and different) index of refraction, and make each layer one-half wavelength thick. The one-half-wavelength thickness means that the light that penetrates the first layer and is reflected by the interface goes through a whole wavelength by the time it makes the round trip, so it constructively-interferes with the reflection from the air-coating layer. If you want a nice, 99.999% reflective surface, you use hundreds of layers of materials in half-wavelength thick coatings that are made of materials whose index of refraction is a couple of percent different, so you maybe get 1% reflection from each layer-interface, and they all add up in-phase because they're all a half-wavelength thick. So you get a nice 99.999% reflectivity *at that wavelength*.
What happens when you shine a different wavelength light at that coating, though? The layers aren't one-half wavelength thick anymore. Those hundreds of interfaces aren't reflecting at the same phase anymore. You get absorption where you'd designed for reflection. You're correct, the energy doesn't disappear, it creates heat in the coating (and substrate) if it's a low-power laser, and if it's a weapons-class laser (like on ABL), then the energy gets coupled to the coating (and substrate) and the coating blows off, and leaves a scorched substrate which then absorbs the MWatt-class laser power and it melts/vaporizes from the heat, and if that's a missile carrying anthrax to SKorea, then the missile blows up within seconds thereafter and drops the anthrax a few miles from where the missile was launched.
So if the NKoreans apply a High-Energy/High-Reflectivity coating to their missiles, and they guess wrong about the wavelength of the laser we've published in Popular Mechanics, then that HE/HR coating would be worse than worthless. And I've mentioned a couple of times that green laser pointers don't use green lasers to make the green laser beams, they use an IR laser diode and a "Frequency-Doubler" (non-linear optical material) that takes some of the IR and makes it visible-green. (There are other ways of changing the wavelength of a laser besides using "doublers" but I think I've disclosed enough material for one day.)
From the top:
From the Basic Optics book, look for what happens when light traverses a boundary between two clear substances which have different indices of refraction: the amount of light reflected is proportional to the ratio of the different refractive indices. Think of water in an aquarium, you look in and you get a strong reflection off the glass from the water-side, especially.
The coatings applied to optical surfaces are like that, but they use one other trick. They carefully tailor the thickness of the layers applied. If they want an antireflective coating at a certain wavelength of light, then they make the layer one-quarter wavelength thick. That means that the reflection from the inner surface ends up traversing that layer twice, making it one-half a wavelength out of phase with the reflection from the front surface. (If it's a one-layer thick antireflective coating, they choose a material that's clear at the wavelength desired to transmit, but also that it has an index of refraction that's the harmonic mean of the air and the glass (or whatever the substrate is), so that the two reflections, from the front surface (air-coating) is the same strength as the back surface reflection (coating-substrate). These are what's on camera lenses, and they work nicely over the visible range of light. They don't work in IR at all, though (something that the Ghost Hunters need to learn), because the longer wavelengths make that "1/4-wavelength-thick" coating less than a quarter-wavelenght thick, and so the reflections from the two surfaces don't cancel each other out as designed. They're too close together, so they tend to add in-phase, almost like there isn't an AR coating on it at all.
In a reflective coating, it's the same principle. Make the layers of two (or more) materials that are transmissive at the design-to wavelength, but of intermediate (and different) index of refraction, and make each layer one-half wavelength thick. The one-half-wavelength thickness means that the light that penetrates the first layer and is reflected by the interface goes through a whole wavelength by the time it makes the round trip, so it constructively-interferes with the reflection from the air-coating layer. If you want a nice, 99.999% reflective surface, you use hundreds of layers of materials in half-wavelength thick coatings that are made of materials whose index of refraction is a couple of percent different, so you maybe get 1% reflection from each layer-interface, and they all add up in-phase because they're all a half-wavelength thick. So you get a nice 99.999% reflectivity *at that wavelength*.
What happens when you shine a different wavelength light at that coating, though? The layers aren't one-half wavelength thick anymore. Those hundreds of interfaces aren't reflecting at the same phase anymore. You get absorption where you'd designed for reflection. You're correct, the energy doesn't disappear, it creates heat in the coating (and substrate) if it's a low-power laser, and if it's a weapons-class laser (like on ABL), then the energy gets coupled to the coating (and substrate) and the coating blows off, and leaves a scorched substrate which then absorbs the MWatt-class laser power and it melts/vaporizes from the heat, and if that's a missile carrying anthrax to SKorea, then the missile blows up within seconds thereafter and drops the anthrax a few miles from where the missile was launched.
So if the NKoreans apply a High-Energy/High-Reflectivity coating to their missiles, and they guess wrong about the wavelength of the laser we've published in Popular Mechanics, then that HE/HR coating would be worse than worthless. And I've mentioned a couple of times that green laser pointers don't use green lasers to make the green laser beams, they use an IR laser diode and a "Frequency-Doubler" (non-linear optical material) that takes some of the IR and makes it visible-green. (There are other ways of changing the wavelength of a laser besides using "doublers" but I think I've disclosed enough material for one day.)
QUOTE (wcelliott+Jul 20 2008, 09:51 PM)
What happens when you shine a different wavelength light at that coating, though? The layers aren't one-half wavelength thick anymore. Those hundreds of interfaces aren't reflecting at the same phase anymore. You get absorption where you'd designed for reflection. You're correct, the energy doesn't disappear, it creates heat in the coating (and substrate) if it's a low-power laser
Ok, we're getting close to an answer. I've included what I think is the relevant part of your answer; I think I understand the basics that you talked about. e.g.:
no, and they work better in the green part of the spectrum (520-570nm) than in the red/blue parts, which is why they have a purple tinge (reflection in the red and blue parts of the spectrum).
What I'm now left with is this; why does the configuration you've described above absorb and not simply behave 'anti'reflectively' like you described in one of your other paragraphs? I'm happy to restrict the situation to low-power, it's less complicated.
Or to re-state the question: "What differs between the situation here where the layers behave overall absorptive and the situation you described earlier where the layers behave overall 'anti-reflectively'?"
Ok, we're getting close to an answer. I've included what I think is the relevant part of your answer; I think I understand the basics that you talked about. e.g.:
QUOTE
These are what's on camera lenses, and they work nicely over the visible range of light. They don't work in IR at all, though
no, and they work better in the green part of the spectrum (520-570nm) than in the red/blue parts, which is why they have a purple tinge (reflection in the red and blue parts of the spectrum).
What I'm now left with is this; why does the configuration you've described above absorb and not simply behave 'anti'reflectively' like you described in one of your other paragraphs? I'm happy to restrict the situation to low-power, it's less complicated.
Or to re-state the question: "What differs between the situation here where the layers behave overall absorptive and the situation you described earlier where the layers behave overall 'anti-reflectively'?"
In camera lenses, you don't usually expect to receive incident light at flux levels which would damage the lens (substrate). If you focus a megawatt-class laser at a common antireflective-coated camera lens, it'll blow itself to bits.
High-energy optics requires HE/HR coatings as mirrors, and the reason for hundreds (or thousands) of layers is to distribute the electric fields over all the layers. You could conceivably use a reflective coating of a single layer, but it'd blow-off from the high electric field generated by the incident power.
There's considerable "art" in High-Energy optics. There are few companies capable of making them. I worked on one program for JPL which had to buy a special-coated mirror from a supplier in France, because there were no US sources up to the challenge.
Incidentally, my comment about the Ghost Hunters was in reference to an amateur photographer who "captured images of apparitions" using a common camera with IR film. His "apparitions" were due to the anti-reflective coating not working at IR wavelengths, and there was a light in each of the pictures which produced "lens-flare", which he interpreted as "apparitions".
High-energy optics requires HE/HR coatings as mirrors, and the reason for hundreds (or thousands) of layers is to distribute the electric fields over all the layers. You could conceivably use a reflective coating of a single layer, but it'd blow-off from the high electric field generated by the incident power.
There's considerable "art" in High-Energy optics. There are few companies capable of making them. I worked on one program for JPL which had to buy a special-coated mirror from a supplier in France, because there were no US sources up to the challenge.
Incidentally, my comment about the Ghost Hunters was in reference to an amateur photographer who "captured images of apparitions" using a common camera with IR film. His "apparitions" were due to the anti-reflective coating not working at IR wavelengths, and there was a light in each of the pictures which produced "lens-flare", which he interpreted as "apparitions".
Ok, so can I assume that your explanation works only with high energy incident light? That's what it sounds like you're saying.
So let's limit ourselves to a low power laser; why does the situation you described behave absorptively and not anti-reflectively?
What differs between the absorptive case and the anti-reflective case? They seem very similar to me.
So let's limit ourselves to a low power laser; why does the situation you described behave absorptively and not anti-reflectively?
What differs between the absorptive case and the anti-reflective case? They seem very similar to me.
In the general case, some light gets reflected, some light gets transmitted to the substrate, and some light gets absorbed by the coating.
With High-Energy dielectric mirrors, they usually choose a substrate that's as transparent as possible at the intended wavelength, so the power goes straight through (except for that which gets absorbed, heating the substrate). It's common to have to cool the substrate (hence my patent in face-cooled optics for high-energy laser optics). Sometimes you don't have to, but in laser weapons, it's more common than not.
In low-energy optics, it's the same general case - some gets transmitted to the substrate (e.g., glass or aluminum, which itself transmits or absorbs or reflects the light), some gets reflected by the coating, and the rest gets absorbed by the coating.
You're correct in stating that the power doesn't disappear, it goes someplace, and only has those three options (excluding photosynthesis). Most normal lighting doesn't have enough power to damage a lens coating, or the glass/aluminum substrate, so the heat buildup is negligable. In laser weapons, that's not the case, the heat buildup would melt the substrate without an effective reflective coating, and as I've described, they're wavelength-specific because their very design is based on an assumed wavelength for determining the structural thicknesses of the coating layers. For a megawatt-class laser, it's anybody's guess which happens first, the coating blowing off or the substrate melting/vaporizing. It depends on the specifics of the coating and the substrate.
I really can't go into this particular topic any deeper, as "kill mechanisms" of laser weapons systems is generally the sort of thing that we aren't supposed to go into, as it'd be considered helping the enemies of the US. (Obviously.)
With High-Energy dielectric mirrors, they usually choose a substrate that's as transparent as possible at the intended wavelength, so the power goes straight through (except for that which gets absorbed, heating the substrate). It's common to have to cool the substrate (hence my patent in face-cooled optics for high-energy laser optics). Sometimes you don't have to, but in laser weapons, it's more common than not.
In low-energy optics, it's the same general case - some gets transmitted to the substrate (e.g., glass or aluminum, which itself transmits or absorbs or reflects the light), some gets reflected by the coating, and the rest gets absorbed by the coating.
You're correct in stating that the power doesn't disappear, it goes someplace, and only has those three options (excluding photosynthesis). Most normal lighting doesn't have enough power to damage a lens coating, or the glass/aluminum substrate, so the heat buildup is negligable. In laser weapons, that's not the case, the heat buildup would melt the substrate without an effective reflective coating, and as I've described, they're wavelength-specific because their very design is based on an assumed wavelength for determining the structural thicknesses of the coating layers. For a megawatt-class laser, it's anybody's guess which happens first, the coating blowing off or the substrate melting/vaporizing. It depends on the specifics of the coating and the substrate.
I really can't go into this particular topic any deeper, as "kill mechanisms" of laser weapons systems is generally the sort of thing that we aren't supposed to go into, as it'd be considered helping the enemies of the US. (Obviously.)
QUOTE (wcelliott+Jul 23 2008, 02:34 AM)
In the general case, some light gets reflected, some light gets transmitted to the substrate, and some light gets absorbed by the coating.
With High-Energy dielectric mirrors, they usually choose a substrate that's as transparent as possible at the intended wavelength, so the power goes straight through (except for that which gets absorbed, heating the substrate). It's common to have to cool the substrate (hence my patent in face-cooled optics for high-energy laser optics). Sometimes you don't have to, but in laser weapons, it's more common than not.
In low-energy optics, it's the same general case - some gets transmitted to the substrate (e.g., glass or aluminum, which itself transmits or absorbs or reflects the light), some gets reflected by the coating, and the rest gets absorbed by the coating.
You're correct in stating that the power doesn't disappear, it goes someplace, and only has those three options (excluding photosynthesis). Most normal lighting doesn't have enough power to damage a lens coating, or the glass/aluminum substrate, so the heat buildup is negligable. In laser weapons, that's not the case, the heat buildup would melt the substrate without an effective reflective coating, and as I've described, they're wavelength-specific because their very design is based on an assumed wavelength for determining the structural thicknesses of the coating layers. For a megawatt-class laser, it's anybody's guess which happens first, the coating blowing off or the substrate melting/vaporizing. It depends on the specifics of the coating and the substrate.
I really can't go into this particular topic any deeper, as "kill mechanisms" of laser weapons systems is generally the sort of thing that we aren't supposed to go into, as it'd be considered helping the enemies of the US. (Obviously.)
Ok, but you're avoiding the question. Nobody is denying that at high energies, a lot of energy will get absorbed. At low energies, some energy will get absorbed. But this is independent of whether the medium is fundamentally reflective or transmissive.
Your argument was that the dimensions of the layers would optically alter whether light of a particular wavelength is reflected or absorbed. You are yet to explain why light of that particular causes the medium to behave absorptively and not anti-reflectively, as your own previous explanation suggests it would.
So again, what differs (optically) between the case where the medium is absorptive and the case where the medium behaves anti-reflectively (both of which you have described)?
With High-Energy dielectric mirrors, they usually choose a substrate that's as transparent as possible at the intended wavelength, so the power goes straight through (except for that which gets absorbed, heating the substrate). It's common to have to cool the substrate (hence my patent in face-cooled optics for high-energy laser optics). Sometimes you don't have to, but in laser weapons, it's more common than not.
In low-energy optics, it's the same general case - some gets transmitted to the substrate (e.g., glass or aluminum, which itself transmits or absorbs or reflects the light), some gets reflected by the coating, and the rest gets absorbed by the coating.
You're correct in stating that the power doesn't disappear, it goes someplace, and only has those three options (excluding photosynthesis). Most normal lighting doesn't have enough power to damage a lens coating, or the glass/aluminum substrate, so the heat buildup is negligable. In laser weapons, that's not the case, the heat buildup would melt the substrate without an effective reflective coating, and as I've described, they're wavelength-specific because their very design is based on an assumed wavelength for determining the structural thicknesses of the coating layers. For a megawatt-class laser, it's anybody's guess which happens first, the coating blowing off or the substrate melting/vaporizing. It depends on the specifics of the coating and the substrate.
I really can't go into this particular topic any deeper, as "kill mechanisms" of laser weapons systems is generally the sort of thing that we aren't supposed to go into, as it'd be considered helping the enemies of the US. (Obviously.)
Ok, but you're avoiding the question. Nobody is denying that at high energies, a lot of energy will get absorbed. At low energies, some energy will get absorbed. But this is independent of whether the medium is fundamentally reflective or transmissive.
Your argument was that the dimensions of the layers would optically alter whether light of a particular wavelength is reflected or absorbed. You are yet to explain why light of that particular causes the medium to behave absorptively and not anti-reflectively, as your own previous explanation suggests it would.
So again, what differs (optically) between the case where the medium is absorptive and the case where the medium behaves anti-reflectively (both of which you have described)?
Hello bm1957
Here is a User posted image: User posted image of a dialectic mirror and an excerpt of its associate text:
Hope this helps.
Here is a User posted image: User posted image of a dialectic mirror and an excerpt of its associate text:
QUOTE
Stacks of thin planar layers of appropriate thickness then will reflect a certain wavelength from all interfaces such that a maximum constructive interference occurs, yielding a reflectivity of close to 100%. A plate with such a stack of thin dielectric layers is a dielectric mirror
from this site.Hope this helps.
Thanks, Montec!
QUOTE (Montec+Jul 23 2008, 04:56 PM)
Hello bm1957
Here is a User posted image: <a target='_blank' href='http://www.mih.unibas.ch/Booklet/Lecture/Chapter2/Fig2-7.gif'>User posted image</a> of a dialectic mirror and an excerpt of its associate text: from this site.
Hope this helps.
It doesn't really address the question, does it? We've established how reflectivity of a dielectric works, we're trying to establish if the same material is absorptive at double the design wavelength, or if it's transmissive (anti-reflective).
If it's in that link, I've missed it. If it's been explained, I missed it. With no explanation, wc should apologise for flying off the handle earlier (if there is an explanation forthcoming, wc deserves an apology.)
Here is a User posted image: <a target='_blank' href='http://www.mih.unibas.ch/Booklet/Lecture/Chapter2/Fig2-7.gif'>User posted image</a> of a dialectic mirror and an excerpt of its associate text: from this site.
Hope this helps.
It doesn't really address the question, does it? We've established how reflectivity of a dielectric works, we're trying to establish if the same material is absorptive at double the design wavelength, or if it's transmissive (anti-reflective).
If it's in that link, I've missed it. If it's been explained, I missed it. With no explanation, wc should apologise for flying off the handle earlier (if there is an explanation forthcoming, wc deserves an apology.)
From the Basic Physics book, and from my earlier explanation, whenever there's an interface between two materials that have different refractive indices, you get a reflection of that interface.
From the wave theory of light (the easiest way to look at it), the layers in a reflective coating have to be one-half wavelength thick in order for the reflections from the interfaces between the layers to constructively-interfere.
If you double the wavelength, then the layers will be 1/4-wave thick, and the reflections from the layer interfaces will make a half-wavelength round trip and will *destructively* interfere, making a perfect *anti-reflective* coating. That makes it *not a mirror*, so the energy of the light is absorbed in the coating, making heat from the light.
Under most conditions, the coating is thin and that heat is transmitted to the substrate onto which you've deposited the reflective coating. In most cases, that heat is minimal, virtually impossible to measure.
If, on the other hand, the dielectric mirror is deposited on a missile, and you focus a megawatt-class laser on the missile at a wavelength *other* than that assumed when they chose the coating layer thickness, then a significant fraction of that megawatt heats the coating/substrate, and it's bye-bye missile.
Clear?
From the wave theory of light (the easiest way to look at it), the layers in a reflective coating have to be one-half wavelength thick in order for the reflections from the interfaces between the layers to constructively-interfere.
If you double the wavelength, then the layers will be 1/4-wave thick, and the reflections from the layer interfaces will make a half-wavelength round trip and will *destructively* interfere, making a perfect *anti-reflective* coating. That makes it *not a mirror*, so the energy of the light is absorbed in the coating, making heat from the light.
Under most conditions, the coating is thin and that heat is transmitted to the substrate onto which you've deposited the reflective coating. In most cases, that heat is minimal, virtually impossible to measure.
If, on the other hand, the dielectric mirror is deposited on a missile, and you focus a megawatt-class laser on the missile at a wavelength *other* than that assumed when they chose the coating layer thickness, then a significant fraction of that megawatt heats the coating/substrate, and it's bye-bye missile.
Clear?
Hello bm1957
Are we talking 1/4 wavelength thickness then? A 1/4 wavelength or quarter wave plate will turn plane polarized light into circularly polarized light and back again if the light travels through another quarter wave plate. A mismatch between the incident light and quarter wave plate will generate an elliptically polarized beam output. When the thickness of the plate is equal to 1/2 the incident frequency then there is no change in the polarization.
The change in the index of refraction at the 1/2 wavelength is the key in how dielectric mirrors function. I suspect that a quarter wavelength dialectic mirror will still function (two layers are needed - polarization swapping) but at a reduced efficiency.
Are we talking 1/4 wavelength thickness then? A 1/4 wavelength or quarter wave plate will turn plane polarized light into circularly polarized light and back again if the light travels through another quarter wave plate. A mismatch between the incident light and quarter wave plate will generate an elliptically polarized beam output. When the thickness of the plate is equal to 1/2 the incident frequency then there is no change in the polarization.
The change in the index of refraction at the 1/2 wavelength is the key in how dielectric mirrors function. I suspect that a quarter wavelength dialectic mirror will still function (two layers are needed - polarization swapping) but at a reduced efficiency.
Please note that I was distracted when I replied before, and I wrote "halved" when I meant "doubled". It's correct now, but different from when the post prior to this one was written.
That having been said, there's a big difference between one half-wavelength thick layer and two quarter-wavelength layers. Same net thickness, but one reflects (the half-wavelength coating) and the other is *anti-reflective*.
That having been said, there's a big difference between one half-wavelength thick layer and two quarter-wavelength layers. Same net thickness, but one reflects (the half-wavelength coating) and the other is *anti-reflective*.
QUOTE (wcelliott+Jul 24 2008, 02:39 AM)
If you double the wavelength, then the layers will be 1/4-wave thick, and the reflections from the layer interfaces will make a half-wavelength round trip and will *destructively* interfere, making a perfect *anti-reflective* coating. That makes it *not a mirror*, so the energy of the light is absorbed in the coating, making heat from the light.
I think this is where there is disagreement. Anti-reflective doesn't mean absorptive, it means transmissive. The fact that the waves interfere destructively doesn't mean that they disappear (yes, there may be some absorption by the material, but by design the materials used are highly transmissive, so at *low energies*, absorption will be low) destructive interference just means that the reflection is destroyed. As a strange 'quirk' of quantum electrodynamics, the light 'knows' that if it doesn't get reflected, it just keeps going all the way through and gets transmitted.
I strongly recommend 'QED, the strange theory of light and matter - Richard Feynman' for a better understanding of this, and must conclude that you owe Enthalpy an apology, unless you can come back with a more convincing explanation.
I think this is where there is disagreement. Anti-reflective doesn't mean absorptive, it means transmissive. The fact that the waves interfere destructively doesn't mean that they disappear (yes, there may be some absorption by the material, but by design the materials used are highly transmissive, so at *low energies*, absorption will be low) destructive interference just means that the reflection is destroyed. As a strange 'quirk' of quantum electrodynamics, the light 'knows' that if it doesn't get reflected, it just keeps going all the way through and gets transmitted.
I strongly recommend 'QED, the strange theory of light and matter - Richard Feynman' for a better understanding of this, and must conclude that you owe Enthalpy an apology, unless you can come back with a more convincing explanation.
Sorry I've been away so long, I was writing a spec on a solar-thermal power plant that was due this week.
At low energies, antireflective coatings are used on glass lenses, like camera lenses, and they serve to decrease the reflection at the surface interfacing two media of different indices of refraction. In that instance (low flux, transmissive substrate), the AR coating *does* increase the amount of light that gets to the lens, and it *doesn't* absorb the light.
In the "laser cannon warfare" situation, the substrate isn't transmissive, it's reflective, and presumably not reflective enough to keep the laser from burning a hole through it, otherwise, why the coating?
We've made a few invalid assumptions and skipped over a few steps to get to this point, but High-Energy/High-Reflectivity coatings are, as I'd indicated before, different from AR coatings in more than one way. They use hundreds of layers because one layer won't survive the high-energy, you need the hundreds so that each layer can contribute maybe 1-2% of the reflectivity without blowing itself off the substrate. All those layers makes the bandwidth of the coating's reflectivity very narrow, and I've pointed out several different examples (e.g., the green laser pointer, my patent) where there are ways of getting a beam that's an octave away (or more, or less) than the laser's primary wavelength.
When the laser is an octave away from the HE/HR coating's design-to wavelength, you can't assume that the coating materials are still transmissive. When I was working on SBL/IFX, I saw several HE/HR mirrors that were opaque in the visible light, as they were designed for longer wavelengths (IR), and neither the coating nor the substrate was transmissive at any optical wavelength. They looked black when you tried to see through them, and were only as "shiny" at optical wavelengths as you'd expect anything that flat to be. But even assuming that the coatings *were* as transmissive at lambda/2 or 2*lambda as they were at lambda, that would only mean that the laser's energy would be guaranteed to be delivered right to that "not shiny enough" substrate that we can burn a hole right through, anyway. A reflective coating doesn't work outside its design-to wavelength.
Now, I think I've answered the question(s) managing not to call anyone a liar in the process, and I've provided ample substantiation for my position (and identity).
PS - I've read QED, and several other of Feynman's works. He's something of a personal hero to me.
At low energies, antireflective coatings are used on glass lenses, like camera lenses, and they serve to decrease the reflection at the surface interfacing two media of different indices of refraction. In that instance (low flux, transmissive substrate), the AR coating *does* increase the amount of light that gets to the lens, and it *doesn't* absorb the light.
In the "laser cannon warfare" situation, the substrate isn't transmissive, it's reflective, and presumably not reflective enough to keep the laser from burning a hole through it, otherwise, why the coating?
We've made a few invalid assumptions and skipped over a few steps to get to this point, but High-Energy/High-Reflectivity coatings are, as I'd indicated before, different from AR coatings in more than one way. They use hundreds of layers because one layer won't survive the high-energy, you need the hundreds so that each layer can contribute maybe 1-2% of the reflectivity without blowing itself off the substrate. All those layers makes the bandwidth of the coating's reflectivity very narrow, and I've pointed out several different examples (e.g., the green laser pointer, my patent) where there are ways of getting a beam that's an octave away (or more, or less) than the laser's primary wavelength.
When the laser is an octave away from the HE/HR coating's design-to wavelength, you can't assume that the coating materials are still transmissive. When I was working on SBL/IFX, I saw several HE/HR mirrors that were opaque in the visible light, as they were designed for longer wavelengths (IR), and neither the coating nor the substrate was transmissive at any optical wavelength. They looked black when you tried to see through them, and were only as "shiny" at optical wavelengths as you'd expect anything that flat to be. But even assuming that the coatings *were* as transmissive at lambda/2 or 2*lambda as they were at lambda, that would only mean that the laser's energy would be guaranteed to be delivered right to that "not shiny enough" substrate that we can burn a hole right through, anyway. A reflective coating doesn't work outside its design-to wavelength.
Now, I think I've answered the question(s) managing not to call anyone a liar in the process, and I've provided ample substantiation for my position (and identity).
PS - I've read QED, and several other of Feynman's works. He's something of a personal hero to me.
QUOTE (wcelliott+Aug 2 2008, 05:39 PM)
Now, I think I've answered the question(s) managing not to call anyone a liar in the process, and I've provided ample substantiation for my position (and identity).
I guess we'll have to agree to disagree there. I won't go so far as to say you are wrong; if what you have said personally is true then you are for more experienced than I.
However, you've not even come close to explaining your point of view in an understandable way. I'm no expert, but I'm certainly no lay-man either, and you have not convinced me. It has even appeared that you have avoided direct questions and requests (difference between two mechanisms, sticking to low energy) at times. The only thing that comes to explaining your position seems to rely on varying transmission of the substrate with wavelength... which is clearly outside the scope of the original disagreement.
[EDIT]
That's certainly a sidestep from what you were arguing in this post. [/EDIT]
I guess we'll have to agree to disagree there. I won't go so far as to say you are wrong; if what you have said personally is true then you are for more experienced than I.
However, you've not even come close to explaining your point of view in an understandable way. I'm no expert, but I'm certainly no lay-man either, and you have not convinced me. It has even appeared that you have avoided direct questions and requests (difference between two mechanisms, sticking to low energy) at times. The only thing that comes to explaining your position seems to rely on varying transmission of the substrate with wavelength... which is clearly outside the scope of the original disagreement.
[EDIT]
QUOTE
In the "laser cannon warfare" situation, the substrate isn't transmissive, it's reflective
That's certainly a sidestep from what you were arguing in this post. [/EDIT]
QUOTE
QUOTE
In the "laser cannon warfare" situation, the substrate isn't transmissive, it's reflective
That's certainly a sidestep from what you were arguing in this post. [/EDIT]
In the "laser cannon warfare" situation, the substrate isn't transmissive, it's reflective
That's certainly a sidestep from what you were arguing in this post. [/EDIT]
In "laser cannon warfare", we're using megawatt-class lasers to attack missiles. Missiles aren't made from transmissive materials, they're generally made from aluminum. I've acknowledged that aluminum can be polished to 93% reflectivity, but I've said that 93% isn't enough for the missile to survive. That's where the 99.999% reflective coatings got mentioned. I said that they'd be ineffective at wavelengths other than that one wavelength where the coating would be 99.999% reflective, and pointed out that the same coating would be worse than nothing at other wavelengths, and pointed out that changing the wavelength of a laser is done routinely in, for example, green laser pointers (which use IR lasers as pumps for non-linear optical media which changes the wavelength from IR to green).
http://www.repairfaq.org/sam/laserpic/glpdpics.htm
Please note in the above link that the laser used to generate a green laser is at 808nm, while the green laser is at 532nm. It isn't merely doubled in frequency, there's an intermediate step that changes the 808nm to 1064nm, then the doubler changes it to half of 1064nm (532nm). This was what I'd strongly recommended that Enthalpy look up on his own before continuing the argument. He apparently didn't bother do a five-minute google search, as I'd advised.
I don't mind when people are factually incorrect, and I don't get personal when I correct a mistake, but I do take insults personally, and calling me a liar because I know more about optics is an insult.
PhysOrg scientific forums are totally dedicated to science, physics, and technology. Besides topical forums such as nanotechnology, quantum physics, silicon and III-V technology, applied physics, materials, space and others, you can also join our news and publications discussions. We also provide an off-topic forum category. If you need specific help on a scientific problem or have a question related to physics or technology, visit the PhysOrg Forums. Here you’ll find experts from various fields online every day.
To quit out of "lo-fi" mode and return to the regular forums, please click here.