Fluctuations of the intensity of radiation from a single-frequency injection laser with an external dispersive resonator

Investigations of fluctuations of the intensity of radiation emitted by a single-frequency injection laser demonstrated that the fluctuations were due to beats of a coherent field with superradiant spontaneous radiation. The level of fluctuations was found to decrease on increase in the output power of the laser under advanced lasing conditions. Moreover, there was a relative spectral shift of the frequency of the superradiant modes of the external resonator, which depended on the laser radiation power. An explanation of this behavior was based on a mechanism of a nonlinear interaction of fields in the active region of a laser diode. It was found that when the output power of a laser was quite high (~6 mW), the level of such fluctuations did not exceed by more than 4 dB the shot noise.