At 2 K, at low intensity, and in good quality samples, the source of the exciton-polariton dipole dephasing time (or phase coherence time) is found to be extrinsic in nature and due to dephasing elastic collisions for excitation below the A-transverse-exciton frequency, and purely intrinsic and due to quasi-elastic collisions with acoustical phonons for excitation above the longitudinal A-exciton frequency. The damping increases linearly with detuning for excitation above the A longitudinal exciton frequency.

• Received 1 December 1986

DOI:https://doi.org/10.1103/PhysRevLett.58.1776