Polarization Properties of Biexciton Luminescence and Two‐Photon Raman Emission in CuCl

The polarization properties of biexciton luminescence and resonant two‐photon Raman emission are studied. For the first time, direct evidence on the biexciton distribution function in momentum space is obtained. Raman lines are found to be due to a four‐particle process where all momenta are well defined. The origin of the biexciton luminescence lines is, on the contrary, a cold gas of biexcitons, which is subjected to elastic and inelastic collisions. Its distribution function is wide spread but not yet isotropic in the momentum space.