Quality of the Stokes beam in stimulated Raman scattering

Stokes beam quality as obtained by stimulated Raman scattering is investigated numerically using various pump-beam profiles. It is found that the quality of the Stokes beam, expressed by M/sup 2/, is often roughly the same as the pump beam. For pump beams with Gaussian-Hermite modes, TEM/sub 00/ and TEM/sub 01/, the Stokes beam has the same-phase relation and M/sup 2/ as the pump beam. However, the TEM/sub 11/ pump beam, which has an M/sup 2/ of 3.0, gives a Stokes beam with a higher M/sup 2/, namely 3.7, and a distorted phase relation. For a Gaussian-Schell model beam, the M/sup 2/ of the Stokes beam is equal to that of the pump if the Stokes has the same wavelength as the pump; if the ratio of the Stokes and the pump wavelength increases, then the M/sup 2/ of the Stokes beam decreases. Experimental verification was obtained using a pump beam with an M/sup 2/ of 8.7 and a wavelength of 1.06 /spl mu/m. The generated Stokes beam at 1.54 /spl mu/m had an M/sup 2/ of 5.8, which agrees well with the numerical M/sup 2/ of 6.1.<
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