Tunable stimulated electronic Raman scattering in alkali metal vapours

Cotter, David (1976) Tunable stimulated electronic Raman scattering in alkali metal vapours. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Stimulated electronic Raman scattering (SETS) is investigated hs a new simple method of generating tunable infrared radiation for spectroscopic applications. Experiments using SEES in potassium and caesium vapours demonstrate that wide ranges of infrared tuning are possible with pulsed dye lasers as the pumping source. A major part of the wavelength range 0.2-15 µm is covered using caesium, with output powers of up to 25kW. A series of experiments with the object of characterising and optimising the performance of the SEES source are described. The radiation generated in the region of 2.7µm in potassium is used to obtain absorption spectra with an infrared resolution of 0.4 cm^-1 . The measured line widths of the generated radiation are in the range 0.3-1.6 cm^-1, depending on the experimental conditions. and indicate the existence of one or more line broadening mechanisms. A number of possible mechanisms are described. Time-resolved observations reveal complex spectral and temporal behaviour. A theory for the small signal growth including the diffraction of the pump and Stokes radiation is developed, and shows that this diffraction has an important influence on infrared generation by SEES. The effects of competing processes are discussed, and a simple theory for the saturation behaviour which includes both pump depletion and saturation of the atomic levels is used to explain the main features of the variation of the output energy with tuning. The effects of the spin-orbit splitting of the intermediate 1nvels on the resonant enhancement and polarisation properties of SEES are investigated. Finally the SEES technique is assessed and compared with other types of tunable infrared source.

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