DISPERSIONLESS, HIGHLY SUPERLUMINAL PROPAGATION IN A MEDIUM WITH A GAIN DOUBLET

In the region between two lines of a doublet of an inverted medium, th ere exists a point of zero group-velocity dispersion, where highly sup erluminal effects may be observable without significant gain, loss, di stortion, or broadening. The results of this group-velocity analysis h old for sufficiently narrow-band, analytic pulses, and do not constitu te a violation of causality, although the group, ''signal,'' and energ y velocities as defined by Sommerfeld and Brillouin may all exceed c o r even become negative. No sharp disturbance in the pulse (a real sign al) could propagate faster than light, but the scheme offers an unusua l noiseless amplification scheme for the leading edge of a pulse, both at the classical and at the single-photon level.