Spectral features of anti-Stokes and Stokes modes generated by stimulated Raman scattering in liquid toluene

Abstract

Stimulated Raman scattering leading to the generation of four first-order Stokes modes at shifts of 862.9, 1035, 2967 and 3086 cm−1, one second-order Stokes mode at a shift of 2032.5 cm−1 and one first-order anti-Stokes mode at a shift of 946.3 cm−1 has been measured in an experiment using liquid toluene. The observed shifts are assigned to the earlier reported Raman shifts of toluene at 786, 1006, 2979, 3060 cm−1 due to ring-breathing mode, ring deformation mode, CH3 stretching mode and CH stretching mode, respectively. Simultaneous measurement of all the Raman modes, including the second-order Stokes and first-order anti-Stokes, and their correct assignment to the vibrational modes of toluene is not reported widely in earlier work. The Raman modes generated from toluene emerge as concentric rings of different diameters. The phase-matching angle for anti-Stokes generation is thus measured and compared with the expected value from calculation. The spectral broadening observed near two of the modes is explained with the help of Raman-active modes of toluene reported earlier by others. Raman shifts, threshold levels, gain and beam profile of all the modes, along with the phase matching of the anti-Stokes mode, are reported.