Polariton Wave Packet Propagation in the Exciton Resonance of a Semiconductor

This paper reports the first experimental observation of "slow" pulse propagation in the exciton-polariton resonance of a direct-gap semiconductor. The propagation delay of short light pulses transmitted through a 3.7-{μ}m-thick GaAs crystal was measured directly with a cross-correlation technique. Polariton group velocities from cvac3.6 down to cvac2000 were found when the wave-packet center frequency was tuned through the $n=1$ exciton resonance.