Asymmetric spectral broadening of sub-picosecond laser pulse in BaWO4 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 BaWO4 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 BaWO4 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 dear 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 BaWO4, is of orientational nature. The nonlinear refraction coefficient and its decay time following from our experiments with BaWO4 were estimated as n(2) approximate to 6.4.10(-15) cm(2)/W and tau(NL) approximate to 0.35 ps. (C) 2021 Optical Society of America

Automated summary

The spectral broadening of a 0.3 ps 515 nm laser pulse in highly Raman-active BaWO4 crystal and fused silica shows significantly different behaviors with respect to incident pulse energy. The data obtained provide evidence of stimulated Raman scattering slowing down spectral broadening induced by self-phase modulation, and also suggest that the mechanism of Kerr nonlinearity in BaWO4 is of orientational nature. The nonlinear refractive coefficient and decay time were estimated to be n(2) approximately 6.4×10(-15) cm(2)/W and tau(NL) approximately 0.35 ps from experiments with BaWO4.