Relaxation of Excitonic Molecules Generated by the Giant Two-Photon Laser Excitation in CuCl

Abstract

Forward Raman scattering of excitonic molecule in CuCl has been studied at the giant two-photon excitation with using laser light having a wave vector K₀ but three different half band-widths, 0.2, 1.4 and 2.5 meV. In cases of laser excitation with broader half band-widths, the Raman and luminescence processes coexist and give emission lines called (LEP)_R and (LEP)_B, respectively. Both lines show the similar dependence of energy change upon the scattering angle. The (LEP)_R and (LEP)_B lines show red and blue shift, respectively, with the increase of laser excitation intensity. The excitonic molecule-state generated at K=2K₀ is responsible for the (LEP)_R line, while the (LEP)_B line is considered to arise from a state having a certain K value smaller than 2K₀. Excitonic molecules generated coherently by the giant two-photon excitation are assumed to relax towards K=0 with keeping their individual momentum at almost the same value.