Dark pulse formation in a quantum-dot laser

The laser emission of an InAs/GaAs quantum-dot laser after injection of a nonresonant optical pulse is time resolved using femtosecond upconversion. The injected pulse burns a hole into the gain spectrum that leads to an ultrafast redistribution of carriers away from the lasing wavelength, thereby generating a spatial domain of reduced laser intensity. This domain propagates through the laser, is reflected at the facets, and thus repeats periodically in the output of the quantum-dot laser, forming a train of dark pulses. As a slower response to the optically induced perturbation, gigahertz-frequency relaxation oscillations are observed.