Abstract

Several experiments were reported in which the dephasing times of excitons in quantum wells (QWs) were measured by time-delayed four- wave mixing (TDFWM).^1-4 The various pulse widths and polarizations used in these experiments gave differing results. We report results of an experiment in which the effects of laser polarization and wavelength on TDFWM (echo) in excitons were identified and quantified. The experiment involves a planar phase-matching arrangement in which the two 4-ps laser pulses propagate in the two arms of a Michaelson interferometer, which is equipped with a delay line and the necessary polarization-controlling optics. The pulses arc focused on the cryogenically cool (4.2 K). GaAs/AlGaAs QW sample at a small angle. Each beam is chopped at a different frequency and the generated FWM signal beam is detected on a P-I-N photodiode, is preamplified, and is measured at the sum frequency on a lock-in amplifier.

© 1991 Optical Society of America