Generation of Anti-Stokes Radiation in the Higher Order Coherent Raman Processes

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Abstract
The momentum-matching conditions in the higher order coherent Raman processes are re-examined. It is shown that when the momenta in these conditions are correctly interpreted as corresponding to the propagation vectors of the waves in the presence of interaction, the matching conditions should always be satisfied exactly in these Raman processes. It is also shown that Maxwell's equations lead directly to a set of coupled wave equations which describe the coupling of the Stokes and anti-Stokes waves in the Raman laser medium. The results obtained from these equations reduce in the limiting cases to the results of Bloembergen and Shen obtained on the basis of their coupled amplitude equations. A numerical example is given to illustrate the relative importance of the formal results. Finally, preliminary experimental results on the generation of anti-Stokes radiation in optical waveguides filled with various Raman liquids are given. We believe these results demonstrate that the volume amplification effect due to the higher order Raman processes is observed.