Efficient conical emission of stimulated Raman Stokes light generated by a Bessel pump beam

Stimulated Raman scattering in H ₂ gas was studied with a Bessel pump beam, which was generated with a binary phase grating. The first Stokes light was emitted along the surface of a cone, the angle of which was equal to the cone angle of the Bessel pump beam multiplied by the ratio of the wavelengths of the Stokes and pump beams. High conversion efficiency into the first Stokes light of as much as 60% was achieved, indicating that the complete Bessel $J_0$ mode of the pump beam is involved in the stimulated scattering process.