Detailed experiments on helium-neon FM lasers

Results are reported on the detailed measurements of the operating characteristics of an He-Ne FM laser oscillating at 6328Å. Experiments were performed in both the "phase-locked" and the "FM" regions of operation, with particular emphasis on the FM region. In the phase-locked region, the pulsed output of the FM laser was observed and studied. In the FM region, measurements were made to study the laser power output, modulation index, and distortion (deviation from an ideal FM signal) as functions of the amplitude and frequency of the applied phase perturbation. Most of these experiments were performed under conditions of low laser excess gain (relatively few modes above threshold for the free-running laser); however, the results are useful for predicting the behavior of FM laser operation with larger excess gain. In addition to describing the practical operation of an FM laser, these experiments provide a check on the applicability of the FM laser theory of Harris and McDuff. An exact quantitative comparison between theory and experiment was not attempted, but the qualitative agreement is very good.