Picosecond optical detection of longitudinal spatial hole burning in an AlGaAs semiconductor laser

The author reports the observation of spatially and temporally resolved carrier dynamics in the cavity of a top-surface AlGaAs laser using a modified picosecond differential phase-contrast confocal microscope, which has a single optical probe spot. The sample in the experiment was an AlGaAs crank transverse junction stripe laser. It was prebiased below threshold, and a 2-mA, 100-MHz sine wave signal was used to modulate the charge density within the cavity. The optical probe beam was focused onto the top of the AlGaAs laser sample and x-y scanned across its surface. The measurements show uniform charge density along the edges of the laser cavity and longitudinal spatial hole burning along the laser cavity center. The temporal variation of carriers within the laser cavity was also observed by focusing the picosecond 1.3- mu m laser probing spot to the center of the device. The measurements demonstrate that the internal charge level overshoots and then clamps at the threshold level, where the amount of overshoot is proportional to the overdrive current.