Time-resolved phonon-assisted stimulated emission in quantum-well heterostructures

Summary form only given. The authors report the observation of time-resolved photo-pumped operation of phonon-assisted stimulated emission in a series of AlGaAs-GaAs single quantum wells with different well thicknesses (20, 34, and 54 AA). The temporal characteristics of the phonon-assisted stimulated emission are distinct from the laser operation of the confined particle states in that the phonon-assisted process is always delayed in time (30-80 ps) and has a larger temporal full width at half-maximum. Also, lasing on the confined particle states is quenched as the lasing on the phonon sidebands begins. Data are presented on the emission intensity versus wavelength versus time and the dependence of the relative (and absolute) delay times as a function of excitation power and sample geometry. The delay time is uncorrelated with the sample geometry (and thus photon lifetime in the cavity) but is correlated with the excitation power (capacity to generate phonons). The delay is interpreted to be the time necessary to build up a sufficiently large phonon density (possibly by stimulated phonon emission) to initiate the phonon-assisted stimulated emission, which then dominates the spectral output.