Stimulated Raman scattering spectrum of Gaussian and Bessel light beams

The effect of the real part of the Raman suscep-tibility on the Stokes spectrum excited by Gaussian and Bessel beams is studied theoretically and experimentally. This part of the susceptibility is shown to be responsible for the increase in the overlap integral of the Stokes beam and the pump beam and, as a result, for the increase in the Raman amplification in the region of frequencies higher than the frequency of the exact Raman resonance. This, in particular, is observed in the spectral shift of the axial component of Raman generation in the case of Bessel pump and Stokes radiation in the case of the Gaussian pump to the high-frequency region. It is shown that the shift caused by the Bessel pump significantly exceeds the shift caused by the Gaussian pump. The conical component in the case of the Bessel pump is generated at the frequency of the exact Raman resonance.