Explanation of the competition between O- and E-wave induced stimulated Raman and supercontinuum in calcite under ultrafast laser excitation

Abstract

Key optical properties of calcite were measured to unravel the difference between stimulated Raman scattering (SRS) and self-phase modulation (SPM) for the supercontinuum (SC) for ordinary (O) wave and extraordinary (E) wave. These properties are group velocity dispersion, walk-off, spontaneous Raman spectra and cross section, optical ${1086}\;{{\rm cm}^{- 1}}$ phonon linewidth, nonlinear susceptibility ($\chi^{3}$), steady-state and transient SRS, and SC caused from SPM. These are investigated for O-waves and E-waves from a 2.7 cm thick calcite crystal. Using 390 fs pulses (${\sim}{0.8}\;\unicode{x00B5}{\rm J}$ pulse energy) at 517 nm, the O-wave produced a stronger sharp SRS peak at ${1086}\;{{\rm cm}^{- 1}}$ and a weaker SC spectrum in the visible range than the E-wave. The salient difference found between the O- and E-waves for SRS and SPM in calcite is attributed to the larger Raman cross section and the size of nonlinear susceptibility ($\chi^{3}$) for O-waves as compared to E-waves.