Linear Pulse Propagation in an Absorbing Medium

Abstract

The pulse velocity in the linear regime in samples of GaP: N with a laser tuned to the bound $A$-exciton line is measured with use of a picosecond time-of-flight technique. The pulse is seen to propagate through the material with little pulse-shape distortion, and with an envelope velocity given by the group velocity even when the group velocity exceeds 3×${10}^{10}$ cm/sec, $\mathrm{equals}\pm \infty$, or becomes negative. The results verify the predictions of Garrett and McCumber.