Linear pulse propagation in an absorbing medium

The pulse velocity in the linear regime in samples of GaP:N with a laser tuned to the bound A-exciton line is measured using 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 x 1010 cm/sec, equals +- infinity, or becomes negative. The results verify the predictions of Garrett and McCumber