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

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 c m -1 phonon linewidth, nonlinear susceptibility ( χ 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 (∼0.8µ J pulse energy) at 517 nm, the O-wave produced a stronger sharp SRS peak at 1086 c m -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 ( χ 3 ) for O-waves as compared to E-waves.