Asymmetric spectral broadening of sub-picosecond laser pulse in BaWO crystal: interplay of self-phase modulation, stimulated Raman scattering, and orientational Kerr nonlinearity.

Spectral broadening of 0.3 ps 515 nm laser pulse in a highly Raman-active crystal and fused silica demonstrates significantly different behavior with the incident pulse energy. While the broadening in fused silica is fairly symmetric with respect to the pump laser pulse wavelength, the Stokes wing broadening in the crystal is 2 times wider than that of anti-Stokes wing, the former demonstrating a step-like increase with the pulse energy. To the best of our knowledge, the obtained data are the first clear evidences of the following facts: (i) stimulated Raman scattering with sufficiently high efficiency of conversion to Stokes components slows down spectral broadening induced by self-phase modulation, and (ii) the mechanism of Kerr nonlinearity, which is responsible for self-phase modulation in , is of orientational nature. The nonlinear refraction coefficient and its decay time following from our experiments with were estimated as ≈6.4.10/ and ≈0.35.