Efficiency of conversion of XeCl laser radiation for SRS in metal vapor and hydrogen gas

One of the most effective methods of obtaining high-power coherent emission in the visible region of the spectrum is to convert UV emission of excimer lasers in stimulated Raman scattering (SRS) by electron transitions of metal atoms and vibrational transitions of hydrogen molecules. At present the maximum conversion efficiency with respect to the number of photons [eta][sub f] was realized in lead vapor, 80% at [lambda] = 458 nm and 88% in hydrogen molecules for S[sub 1] at [lambda] = 352 nm. At the same time the conversion efficiency in other metal vapors, and also in higher hydrogen Stokes components S[sub 2], S[sub 3], etc. is much lower than the limiting values for Ba, [eta][sub f] [approx equal] 21%, and for S[sub 2] and S[sub 3] respectively [eta][sub f] = 68% and 50%. It is quite difficult to determine from experimental data the optimal conditions for realizing the best efficiency of conversion into some particular component, or to compare these efficiencies, owing to the differences between the experimental conditions and the recording procedures. In many cases the causes of different conversion efficiencies in SRS remain completely unexplained. The level of the realized SRS energy does not exceed as a rule a hundred millijoules, and the pulse duration tens of nanoseconds. The authors present here the results of an experimental investigation of SRS efficiency in metal vapor and in hydrogen, using the pumping beam of a high-grade millijoule XeCl laser with pulse duration 15 nsec and with a joule-level pump beam with pulse duration 200 nsec.