Trigonal LaF₃: a novel SRS-active crystal

Trigonal fluoride LaF₃, widely known as a host crystal for Ln³⁺-lasants, was found to be an attractive many-phonon Raman material and a subject for the investigation of different χ⁽³⁾-nonlinear optical effects. We present the manifestation of photon-phonon interactions related to stimulated Raman scattering (SRS) and Raman-induced four-wave mixing (RFWM) processes, initiated by picosecond excitation at room temperature. Sesqui-octave-spanning Stokes and anti-Stokes frequency comb generation as well as many-step cascaded and cross-cascaded up-conversion χ⁽³⁾-nonlinear processes have been observed. The recorded spectral lines originated by SRS and RFWM are identified and attributed to the three observed SRS-promoting phonon modes. The lower limit of the steady-state Raman gain coefficient for near-IR first Stokes generation was estimated. Moreover, a brief review of known Ln³⁺ : LaF₃ laser crystals and SRS-active fluorides is given. (paper)