Autowaves of the carrier density in PbS$_{1-x}$Se$_x$ injection lasers

An investigation of time dependences of the spectral and spatial distributions of the radiation emitted by pulsed homojunction wide-contact PbS$_{1-x}$Se$_x$ lasers revealed excitation of autowaves (self-oscillatory waves) of the free carrier density at two similar frequencies ($\lesssim$10$^7$ Hz). These autowaves resulted in simultaneous emission of laser radiation of two types, associated with modulation of the refractive index and of the optical gain. The width of the channels was governed by the thickness of the laser diode wafer, but was independent of the resonator width. The transverse (along with $p$-$n$ junction plane) intermode spacing was governed by the amplitude and spatial period (channel width) of the autowaves. A study was made of the influence of the conditions of operation ofthe laser diodes on the autowave parameters. A strong scatter of the threshold current density in a batch of 30 injection lasers with a constant resonator length, formed freshly by four-sided cleaving from a single wafer, was attributed to changes in lateral optical confinement as a result of a change in the resonator width, which was a consequence of interference between the autowaves in the resonator induced by the lateral faces of the crystal.