Propagation of smooth and discontinuous pulses through materials with very large or verysmall group velocities

Abstract

We investigate the propagation of optical pulses through two different solid-state opticalmaterials, ruby and alexandrite, for which the group velocity can be very small() or superluminal ( or negative). We find that for smooth pulses the fractional delay or advancement ismaximized through the use of pulses with durations comparable to the responsetime of the physical process—coherent population oscillations—that leads tothese extreme group velocities. However, we find that the transmitted pulse shapebecomes distorted unless the pulse is much longer or much shorter than thisresponse time. We also investigate the transmission of pulses that possess anabrupt change in pulse amplitude. We find that, to within experimental accuracy,this nearly discontinuous jump propagates at the usual phase velocity of lightc/n, even though the smoothly varying portions of the pulse propagate at the group velocity.