Spin-Sensitive Bleaching and Monopolar Spin Orientation in Quantum Wells

Spin-sensitive bleaching of the absorption of far-infrared radiation has been observed in $p$-type GaAs/AlGaAs quantum well structures. The absorption of circularly polarized radiation saturates at lower intensities than that of linearly polarized light due to monopolar spin orientation in the first heavy-hole subband. Spin relaxation times of holes in $p$-type material in the range of tens of ps were derived from the intensity dependence of the absorption.