Spectrum of a Fabry-Perot resonant cavity containing an active medium.
A Michelson interferometer has been used to measure the visibility curves for the 6328 A neon emission line in a 90% He-10% Ne gas mixture in order to determine the effect of an optical cavity upon the line shape when the medium exhibits a net gain and yet the system is below lasing threshold. An analytical model for the effect of the cavity is proposed and a computer program set up to fit the model to the data. The cavity gain and finesse are used as variable parameters. The same techniques can be applied to a laser and the number of longitudinal lasing modes can be determined; however, in this case the gain and to some extent the finesse are indeterminate.
Hochheimer
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BF
Applied Physics Laboratory, The Johns Hopkins University, Silver Spring, Maryland, USA.