Temporal coherence of the radiation emitted by injection lasers

A modified Michelson interferometer was used to investigate the temporal coherence of the radiation emitted from injection lasers with single- and double-sided heterojunctions. The lasers were operated in the pulsed regime at room and liquid-nitrogen temperatures. The coherence length for the single-mode emission was 8–30 mm at 300°K and below 30–45 mm at 77°K. The use of the apparatus as an intensity interferometer yielded the autocorrelation function of the field and the corresponding function of the intensity of the laser radiation. A comparison of these two autocorrelation functions indicated that the spectral broadening of a single mode was primarily due to phase fluctuations.