Nonlinear (chi((3))+chi((2))) effects in novel borate crystal LiGeBO4 under picosecond laser excitation: High-order Stokes and anti-Stokes generation and self-sum-frequency mixing

摘要

We report the experimental observation of efficient multiple stimulated Raman scattering (SRS) and other (chi((2)) + chi((3))) effects, namely, second harmonic generation, Raman-induced four-wave mixing, and self-sum-frequency mixing, which simultaneously arise in the tetragonal crystal LiGeBO4 under picosecond Nd3+: Y3Al5O12-laser pumping. All the observed Raman-induced lasing wavelengths in the near-IR and visible regions are identified and attributed to the SRS-active vibration mode omega(SRS) = 532 cm(-1) of this novel nonlinear borate. The comparative measurement of the first Stokes steady-state Raman gain coefficient in the near-IR region allows us to tentatively conclude that its maximum value is no less than 4.2 cm/GW as well. We classify the LiGeBO4 acentric compound as a promising medium for up- and down-Raman laser-frequency converters. [References: 47]