title: Superluminal to subluminal transition in the pulse propagation in a resonantly absorbing medium.
abstract: We have examined the propagation of femtosecond laser pulses in an absorbing dye solution through a short to a long range of propagation distance. The transmitted pulses show strong spectral shift and a superluminal to subluminal transition in the propagation velocity keeping its initial shape almost intact. It is verified that the peak velocity is well described by a modified group velocity v(S) defined within the framework of the saddle-point method as well as by a recent prediction of the net group delay of surviving frequency.
authors.affiliation: Department of Physics, Faculty of Science, Shizuoka University, 836 Ohya, Shizuoka 422-8529, Japan.
authors.forename: M A
authors.initials: MA
authors.lastname: Talukder
authors.forename: Y
authors.initials: Y
authors.lastname: Amagishi
authors.forename: M
authors.initials: M
authors.lastname: Tomita