Resonance enhanced cascaded stimulated Raman and Coherent Anti-Stokes Raman scattering of symmetric and antisymmetric O-D vibrations

Stimulated Raman scattering (SRS) of deuteroxide was investigated using a pulsed Nd:YAG laser with a wavelength of 532 nm. After the pump laser passed through the first sample cell (C1), the output light included the transmitted pump beam and the Stokes SRS lights, and the frequency difference between the two self-matched the O-D symmetric and antisymmetric stretching vibration modes. The 1st and the 2nd-order cascaded Stokes and the anti-Stokes SRS (Coherent Anti-Stokes Raman Spectroscopy-CARS) of both two modes were observed. The 2nd-order Stokes SRS and its CARS were firstly observed at a pump energy of 14.79 mJ. The pure Stokes SRS were always collinear with the pump beam along the axial direction. Some ring-like Stokes SRS and CARS, which originated from the four-wave mixing (FWM) processes, were also observed only in the forward direction along with different angles apart from the pump beam direction, respectively. This method not only reduced the SRS threshold but also increased the SRS intensity of the weak vibration mode, resulting in an energy conversion efficiency reaching up to 54%. The technique can be used in a tunable Raman laser.