Radiofrequency spectra of mode beats and fluctuations of the intensity of radiation emitted by an injection laser with an external resonator

A study was made of fluctuations of the intensity of the radiation emitted by a cw AlGaAs injection laser with an external spectrally selective resonator. The laser mode frequencies exhibited considerable fluctuations, which broadened the beat spectrum to at least 100 kHz, i.e., by an amount much greater than the broadening expected due to spontaneous radiation noise. These fluctuations were attributed to an instability of the spatial laser channel in the active medium. It was found that the use of a highly selective resonator made it possible to suppress low-frequency pulsations; this increased the output power in the single-frequency regime.