Can you seperate the o2 from co2 with a laser ? And what would be the best frequency and energy level?

There are many ways of separating O2 from CO2, but each and every one will need at least 94kcal/mol, the energy gained from burning C to CO2 - just in case this was your goal. So a laser would just be a more indirect way of doing it.

Following Enthalpy's point ..

I think photosynthesis is a two photon process. If it turned the impossible into a 'maybe' it might just be worth trying pumping something (say) 10% of the way up and using sunlight to supply the remaining 90%. Just a thought - probably a bad one.

Best wishes -C2.

The problem with using a laser to break the bonds in CO2, is that the products are going to be a hot O2 molecule and a hot carbon atom. Since they are nice and hot, they are likely to react the next time they bump into another atom or molecule. Back to CO2 again.

Perhaps 2-3 weeks ago i was contemplating how to design an laser propulsion system involving CO2 lasers.

The propulsion system has two lasers facing each-other: Laser=> [ CO2] <= Laser

[co2] is the compression zone where
gases from the conventional
fuel-jet propulsion system are further compressed/heated
to even higher temperatures/pressures to produce grater thrust
Larger air inlet feed more air to the superheated thrust causing
an even larger volume of thrust within the propulsion system.

The problem tough is how to prevent the semi-reflective Laser ends
from melting in the [co2] compression zone from the superheated-thrust basting/grazing their surfaces? Transparent zirconia CO2 Lasers?

The matter is open to suggestions:

Sunlight can be very effective for transforming CO2 in CO, just by heating it brutally with a concentrator. You need to separate (absorb?) CO before it recombines with O2, and use the heat from O2 and CO to preheat CO2 before cracking it.

You still have to crack CO, but it needs 26kcal/mol instead of 94kcal/mol for CO2.

And protect all workers.

However, where does the energy come from? Renewables still don't cover the needs. Sequestrating CO2 looks more easy for now.

In a second step, we could make a fuel from CO and other molecules.

Perhaps the laser propulsion system doesn't need any partially reflective surfaces.
It can be open ended angular laser. Imagine an cone within a cone like an funnel within a funnel would be th laser with the thrust from the conventional fuel-jet travels through the center of the CO2 laser.
_ _ <- Laser mirrors
CO2 Plasma laser propulsion system: \\ //
[CO2]



\ / <- Laser mirrors

superheated
plasma
thrust

Possibly even more energy could be pumped into the plasma with large current that causes it to balloon/mushroom magnetically through a ceramic tube thats got + - down it's length that meaning like two long electrodes + - in a pipe

If you react CO2 with H2O you make H2CO3 or carbonic acid. CO2 is soluble in water so just bubble it in. Although still not very easy, one could try for O2 plus H2C0 (formaldehyde). The formaldehyde has energy value, so the amount of energy needed to make O2 would be more. However, the H2CO can be sold in the free market. It is one of the most important precursors for many chemicals. It is also used for embalming. Selling it may offset some of the energy cost. For example, if it is sold to make certain plastics, the CO2 is fixed for generations in landfills. It might be profitable if one was able to make it cheap enough.

The ultimate designer beast would be a yeast that could photosynthesize. It would eliminate the need for 99% of car journeys and make the remaining 1% either impractical or illegal.