Do you know what thermal blooming is TBMR... obviously not from your reply.
http://en.wikipedia.org/wiki/Thermal_lensing
Thermal blooming is when ANY LASER heats the portion of the medium through which it passes (including air). If it's denser in particulate matter, then you'll lose more energy. That energy goes somewhere, if it appears as heat... then you see my point about thermal vision being the most likely to see traces of a laser shot in smoke.
Not only that, it's possible for higher energy photons to produce multiple lower energy photons when freed/excited electrons return to ground. The simplest case is when it bucks it up to one state, then immediately returns producing another photon of the same energy in a different direction. The more complex case, is when it returns to a lower state but not the ground state (possibly more than once) before returning to the ground state. With this method and a proper medium, it is possible for any high energy photon to produce visible photons even though the laser itself isn't visible. This effect doesn't work well in simple atoms like hydrogen.. as the states are very limited and you need precise wavelengths to absorb. But when the spectral absorbtion bands are large, it indicates there's a large number of free energy states. So there is more than just scattering of the lasers wavelength.