Stimulated Raman processes in metal vapours

Abstract

Recent work has demonstrated the potential of stimulated electronic Raman scattering, SERS, as a tunable IR source. The current work has aimed at an extension of the performance of SERS in the two areas of tuning capability and narrower linewidth; to this end a variety of stimulated electronic Raman schemes have been investigated.

Initially the theoretical background of SERS and of various possible competing processes is reviewed. The construction and performance of the dye lasers and heat pipe ovens used for the work are then described, followed by a presentation and discussion of the experimental work performed; this work falls into four main areas.

Firstly the potential of pump and SERS feedback schemes to extend the tuning ranges of an existing alkali metal SERS system, Cs 6s-7s, has been investigated, under non-optimum conditions; results from this appear promising for future work.

Secondly, we have demonstrated for the first time the possibility of obtaining a tunable IR output from a fifth order nonlinear process, stimulated hyper-Raman scattering, SHRS, in Na vapour. Various aspects of theory and behaviour of this process are described.

The advantages of obtaining SERS from an excited initial state have been considered; preliminary results have proved disappointing and have led us to consider possible limiting mechanisms in such processes.

Finally SERS in alkaline earths is considered; only few such schemes would appear to be viable for various reasons. One such scheme in Ba has however yielded a 0.2cm^-1 system-limited SERS linewidth, a narrower SERS linewidth than has previously been attained; indications are that narrower linewidths still may be attainable, although further work will be necessary to verify this. These results also suggest that the optical Stark effect and power broadening have less influence on the Raman linewidth than has previously been thought.

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