A sensitive technique for the determination of optical gain in a DC discharge is outlined. This technique has permitted an investigation of the radial distribution of optical gain at 633 nm in a 3 mm bore discharge with a spatial resolution of around 120 mu m. Results are presented which illustrate the behaviour of this distribution with gas pressure and current.
Experimental cross sections for the simultaneous excitation and ionization of argon to the 4P configuration of Ar' are presented. The data are found to be in considerable disagreement with previous work. Optical excitation functions for the important argon-ion laser lines are given, and the results are compared with the observed relative gains of the lines in a pulsed laser. The cross sections for excitation to the 4P P states of Ar+ are found to have an E dependence with energy in the range 250 -700 eV, in disagreement with the asymptotic behavior predicted from the sudden approximation.
A single-mode frequency stable helium neon laser operating on the 543 nm neon transition was used to probe an electrical discharge in helium neon mixtures. Values for the optical gain at this wavelength were obtained. A comparison with the widely documented behaviour of the 633 nm transition, which shares the same upper state as the 543 nm transition, shows a marked difference in the variation of the optical gain with discharge pressure. This is shown to occur due to the differing behaviour of the lower laser state population densities with pressure. It is proposed that this could be due to the resonance peak in the electron excitation cross section from the ground state to the 2 level. Variation of gain with discharge current is also presented.
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