Intensity Noise in Multimode GaAs Laser Emission

As presently manufactured most GaAs lasers have several lasing modes when the injection current is more than 25% above threshold. This paper describes the noise properties of three groups of multimode lasers operating cw at 10°K, classified on the basis of their sub-threshold spectra. Two main types of intensity noise have been found: (1) low frequency nonstationary noise which occurs when a weak mode is lasing in competition with a strong mode, and (2) broadband stationary noise which occurs when two modes are about equal in intensity. The first type of noise is believed to arise from heat transfer processes in the diodes and dewar, while the second is probably the partition noise which must occur when a photon can be stimulated into one of a number of lasing modes. An important result of these experiments is that the total noise for all modes is very small, being comparable to that for a single mode with the same total power.