Abstract

We report the first time-resolved circular dichroism (CD) studies of nonthermal carrier distributions in GaAs quantum wells. Specifically, we excite a nonthermal carrier distribution at small (30 meV) excess energy using circularly polarized light, and measure the difference between the absorption spectrum obtained for right- and left-hand circular polarization, as a function of time. Previously, it has been shown that when nonthermal distributions are excited in quantum wells, the screening non linearities of the two-dimensional (2D) exciton states are accompanied by a phase-space filling (PSF) component that evolves as the carriers thermalize.¹ The PSF component is a measure of the distribution of occupied states, so that its separate measurement is important for an understanding of the dynamics of thermalization. We show that the circular dichroism response to a screening interaction is zero, whereas the response to phase-space filing is large, making a complete separation of these two effects possible.

© 1992 Optical Society of America