Experimental investigation of the interaction between the electron gas and the excited atoms in a plasma by means of a xenon laser
The study of the interaction between the electron gas and the atoms in excited states has been undertaken for a gas discharge situated in a high gain optical cavity. Of particular interest is the effect of lasering upon this interacti.on. Spatially resolved electron density and electron temperature measurements are presented for a DC excited 3.51 P. (5d 33 -76P22) xenon laser operating in a capillary bore tube over a pressure range of 12.5 to 25.5 m Torr. Anode directed gradi,ents in the electron and neutral gas ,densities are observed and are attributed to electrophoretic effects present in the closed capillary discharge tube. As a result of these gradients, the local population inversion along the axis of the tube varies and, consequently. affects the output of the 3.51 jJ. laser. The influence of lasering upon these low-pressure capillary xenon discharge,s is investigated experimentally by periodically spoiling the Q of the laser cavity by means of a mechanical chopping wheel. It is observed that lasering noticeably alters both the state of the electron gas and the populations of the excited xenon atoms. The cU:t'rent of the DC exci.ted discharge is quenched up to 0.02 per cent during lasering due to laser-induced variations of the electron density and mean energy. Spatially resolved microwave cavity measurements indicate that the electron number density may experience i,ncreases and decreases depending upon local discharge condj.tions. Microwave radiometric measurements reveal that the electron temperature is also affected by lasering. Variations in the microwave cavity Q and in the electron drift velocity due to lasering are in good qualitative agreement with the radiometric data. Confirming spectroscopic observations of laser-induced changes in the spontaneous radiation along the discharge tube are presented. It is demonstrated that excitation of the 6s metastables via electronic impact is instrumental in populating the lower laser level and contributes to a reduction in the local population inversion. Evidence for various radiative and collisional mechanisms responsible for the propagation of the .laser-induced perturbation from the 5d 33 and 6P22 levels to other excited levels is also presented. It is suggested that laser media in general can be analyzed and improved upon by studying the laser-induced changes in the excitation and. relaxation processes.
electron gas, lasers, xenon laser, gas density measurements, plasma, electron and atom interactions
University of Illinois - Urbana-Champaign
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