A practical method is described for inducing fm and phase-locked oscillations in a small He–Ne laser at 6328 Å, with negligible reduction of output power. Internal phase modulation was produced using the electrooptic effect in synthetic crystal quartz. Although crystal quartz has a small electrooptic effect, it has nearly ideal optical properties, and excellent optical surfaces can be produced on it; thus, the laser power is not reduced significantly when the modulator crystal is inserted. The laser spectrum and rf mode beats were observed at several modulation frequencies, and suppression of low-frequency amplitude modulation on the output was obtained with stable fm or phase-locked operation. Agreement with the Harris and McDuff fm theory is discussed.
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