Nonlinear Optical Absorption in GaSe upon Laser Excitation

The nonlinear absorption in GaSe crystals at high optical excitation levels is experimentally studied. A Nd:YAG laser (first and second harmonics, 1064 and 532 nm) and a liquid laser (tuning range 594–643 nm) were used as excitation sources. It is shown that the features observed in the exciton resonance region of the absorption, luminescence, and photoconductivity spectra of GaSe crystals at high optical excitation levels can be explained by exciton–exciton interaction and Coulomb interaction screening by free carriers.