Stimulated two-photon-excited luminescence in stilbene crystals

The energy of the two-photon-excited luminescence has been studied experimentally as a function of the energy of the monochromatic pump–a giant ruby laser pulse–in a molecular stilbene crystal. At pump power densities up to 10⁸ W/cm² this dependence is quadratic. Above 10⁸ W/cm², the behavior deviates from the quadratic law; the two-photon-excited luminescence signal increases sharply with a further increase in the pump power density. The efficiency of the conversion of the laser light (λ = 694.3 nm) into UV two-photon-excited luminescence is η = 0.1%. The coefficient of two-photon absorption is estimated from the experimental data on the transition from spontaneous two-photon-excited luminescence to stimulated luminescence. The result agrees satisfactorily with data in the literature. Conditions for raising the efficiency of the conversion of radiation on the basis of two-photon-excited luminescence in condensed molecular media are analyzed.