lasermaniac
Anyone use laser pointer with telescope to reduce spot size on a target?
midwestern
Do you mean to zero in on a target?
wcelliott
I'm not sure of the question, but you can, indeed, reduce the spot size of a laser pointer on-target at long range by using a telescope.

The limiting factor in diffusion of a laser is the ratio of the primary aperture in wavelengths of the laser light. The smaller a spot you want at a given range, the larger you want the telescope's aperture.

The equation is:

dR = 2.44*R*lambda/D

Where

dR is the size of the spot
R is the range to the target
Lambda is the wavelength of the laser light, and
D is the diameter of the telescope's aperture

So, bigger telescope aperture, smaller spot size on-target. Likewise, shorter wavelength laser, smaller spot-size on-target. (Or less range to target...)
midwestern
I'll verify the equation is the correct means to find a telescope's aperture.
beamq
Laser pointers can help to find the target easily. Green ones is better than red ones .
wcelliott
Amateur astronomers use green laser pointers these days to point out the stars/planets, as the beam is visible in the sky for a long distance.

But I think the question the OP was asking was whether you could connect a laser pointer to a telescope and extend its range, like pointing-out a specific crater on the moon. The answer is yes, that's the same basic principle that laser weapons use to concentrate laser power onto a target (e.g., ICBM) to take it out from a long way off. (I worked on the Space Based Laser program, and worked with the guys who worked on the Air Borne Laser.)

Laser + Telescope = small laser focus at long range
bm1957
QUOTE (wcelliott+Jun 1 2008, 04:13 AM)
I'm not sure of the question, but you can, indeed, reduce the spot size of a laser pointer on-target at long range by using a telescope.

The limiting factor in diffusion of a laser is the ratio of the primary aperture in wavelengths of the laser light. The smaller a spot you want at a given range, the larger you want the telescope's aperture.

The equation is:

dR = 2.44*R*lambda/D

Where

dR is the size of the spot
R is the range to the target
Lambda is the wavelength of the laser light, and
D is the diameter of the telescope's aperture

So, bigger telescope aperture, smaller spot size on-target. Likewise, shorter wavelength laser, smaller spot-size on-target. (Or less range to target...)

That smacks of BS to me.

That equation implies that the optical properties of the telescope play no part in the spot size. Which means the telescope could have no optical properties and have that same effect. You could use a hollow tube to reduce spot size, according to that equation.

Gonna explain where I've fu*ked up?
Confused2
QUOTE (bm1957+)
Gonna explain where I've fu*ked up?

I'm guessing there is an implicit assumption that the optics are 'perfect'. See http://en.wikipedia.org/wiki/Telescope for more details about telescopes. Empty cardboard tubes don't appear in the telescopes section because they aren't telescopes.

Answers to questions like "How fast can a man run?" generally make the implicit assumption that the man isn't locked up in a small room with rubber walls.

Does that help?

-C2.
wcelliott
QUOTE
Answers to questions like "How fast can a man run?" generally make the implicit assumption that the man isn't locked up in a small room with rubber walls.

LOL!!!

True, I was assuming an idealized (diffraction-limited) telescope, so the spot size on-target could easily be bigger than that if you built the telescope wrong (like the Hubble was, originally).

The thing to remember about optics is that light goes both ways through the optics just as easily. If you want to look at a small crater on the moon, you need a big-aperture telescope. That's the main reason the serious telescopes (e.g., Palomar) have big mirrors. (They also collect more light, but that's icing on the cake.)

So if you want to put a megawatt laser on an ICBM after it's launched, you want a big mirror for your telescope so you can see the target clearlyfrom a long way off, then, where you'd see the image of the weakest point of the missile (at the small end of the telescope, like where you'd put film if you were taking a picture of it), you focus your megawatt laser right there and the laser goes in the opposite direction as the light coming *from* the target and is focussed on the aimpoint. The diameter of the focus on the target is calculated using the equation posted prior. Buy a smaller-aperture telescope, and the spot size will be bigger, and at some point, you're just warming up the whole missile rather than burning a hole in its side.

There's always the trade-off where the telescope guys don't want to build a bigger mirror, and the laser guys don't want to build a more powerful laser, so you have to "distribute the misery" equally between them.

It shouldn't come as a surprise, if you think about it, that bigger telescopes are needed to make smaller spots on-target. Bigger telescopes are more expensive. Would you really expect nature to cut us a break, making cheaper telescopes work better than more expensive ones?

Cheers!
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