Propagation of femtosecond pulses in a resonantly absorbing medium: experimental test of a new definition of group velocity

Abstract

Summary form only given. According to the conventional expression the group velocity of optical pulses in resonantly absorbing media can exceed the light velocity in the vacuum and even become negative. Recently a new definition of group velocity has been proposed by means of the saddle point method. We observed the propagation of femtosecond optical pulses in a dye solution and experimentally tested the new definition of the group velocity.