Two-photon interband absorption coefficients in tungstate and molybdate crystals

Abstract

Two-photon absorption (TPA) coefficients were measured in tungstate and molybdate crystals – BaWO4, KGW, CaMoO4, BaMoO4, CaWO4, PbWO4 and ZnWO4 upon different orientations of excitation polarization with respect to the crystallographic axes. Trains of 25ps pulses with variable radiation intensities of third (349nm) harmonics of passively mode-locked 1047nm Nd:YLF laser were used for interband two-photon excitation of the crystals.It was suggested that in the case, when 349nm radiation pumping energy exceeds the bandgap width (hν>Eg), the nonlinear excitation process can be considered as two-step absorption.The interband two-photon absorption in all the studied crystals induces the following one-photon absorption from the exited states, which affects the nonlinear process dynamics and leads to a hysteresis in the dependence of the transmission on the excitation intensity. This fact was taken into account under analysis of the experimental dependences of the reciprocal transmission on the excitation intensity. Laser excitation in the transparency region of the crystals caused stimulated Raman scattering (SRS) not for all the crystals studied. The measured nonlinear coefficients allowed us to explain the suppression of SRS in crystals as a result of competition between the SRS and TPA.