Optical cavity mode dynamics and coherent phonon generation in high- Q micropillar resonators

Abstract

We study the temporal dynamics of photoexcited carriers in distributed Bragg reflector based semiconductor micropillars at room temperature. Their influence on the process of coherent phonon generation and detection is analyzed by means of pump-probe microscopy. The dependence of the measured mechanical signatures on laser-cavity detuning is explained through a model that accounts for the varying light-cavity coupling existent during the ultrashort times that pump and probe pulses dwell within the structure. To do so, we first explain the optical mode dynamics with an electron-hole diffusion model that accounts for the escape of carriers from the probed area, as well as their recombination in the bulk and on the free surfaces. We thus show that the latter is the most influential factor for pillars below $\ensuremath{\sim}10\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$, where 3D confinement of the optical and mechanical fields becomes relevant.