photons can't lose momentum. the photon momentum is determined by it's energy/frequency. And, since it's called quantum physics, a phonton can only be fully absorbed or not at all. You can't absorb only part of a photon (of course, a material can absorb a photon and then spit out another photon of some fraction of the energy of the original, thus effectively absorbing part of the photon). Anyway, there was a thread a couple months ago about this very subject. See here:
http://www.tfproject.org/tfp/showthr...threadid=54544