Hanle-oscillations in the stimulated emission of microcavity laser

We demonstrate a new phenomenon in the emission dynamics of semiconductor microcavities. Hanle-oscillations of the electron spins modulate the gain of microcavities up to extremely high frequencies. So far, we achieved modulation frequencies of 22 GHz with a modulation depth of 96% but we expect much higher pulse repetition rates for higher magnetic fields and for semiconductors with larger electron g factors. In principle, the maximum frequency is only limited by the photon life-time and the maximum gain of the microcavity. The pulse repetition rate is extremely stable since it only depends on the internal clock of the Larmor precession of the electron spins and, therefore, is insensitive to scattering and energy relaxation of the electrons. A microscopic theory is developed to analyze the non-equilibrium carrier and laser dynamics in the framework of Hartree-Fock equations. Measurements with coupled microcavity lasers show a density dependent switching between two distinct oscillation frequencies. The switching turns out to be an interesting method to characterize the active gain medium in coupled microcavities.