Anisotropy of two-photon absorption and Raman generation in Na$_2$Mo$_2$O$_7$ crystal

Two-photon absorption and stimulated Raman scattering in Na$_2$Mo$_2$O$_7$ crystal were studied when irradiated with picosecond laser pulses with a duration of 25 ps. The anisotropy of nonlinear optical properties and width of a band gap in the crystal is revealed. The maximum two-photon absorption coefficient at a wavelength of 523.5 nm was 7.8 cm/GW for radiation with a polarization parallel to the crystallographic axis a. Stimulated Raman scattering in Na$_2$Mo$_2$O$_7$ crystal with a Stokes shift of 939 cm$^{-1}$ when pumped with a wavelength of 523.5 nm was obtained only when excited by radiation with a polarization parallel to the crystallographic axes b and c with Raman gain up to 10.3 cm/GW. The absence of stimulated Raman scattering when excited by radiation with a polarization parallel to axis a, which corresponds to maximal Raman gain coefficient, is due the competition of processes of the stimulated Raman scattering and the two-photon absorption.