Polarization effects and depolarizing collisions in atomic vapour and molecular gas

Polarization effects in gases are investigated by two methods of coherent s pectroscopy-stimulated photon echo in molecular gas and laser-induced fluor escence in atomic vapour. A well developed photon echo experimental techniq ue permitted us not only to measure relaxation rates of population, orienta tion and alignment on degenerated resonant levels in molecular gas but also to study their dependence on particles' longitudinal velocity. The degree of polarization of laser-induced fluorescence in Yb vapour in a mixture wit h Xe proves a large contribution of depolarizing collisions. The complicate d non-exponential fluorescence decay at higher Yb pressures is explained by the radiation trapping.