Propagation of Wave Packet in a Dissipative Dielectric Medium.

摘要

Propagation of a wave packet in a dissipative dielectric medium is studied as an initial value problem. The asymptotic behavior of Gaussian-shaped wave packet is examined by using the saddle point method. Particular interest is given to the velocity of the wave packet defined by x/t (x: observing position, t: arriving time of peak amplitude) and the group velocity, which shows a sharp maximum or even be infinite in the absorption medium. It is found that the velocity of wave packet decreases in the absorption region in contrast to the group velocity which increases there. It is also found that the packet deformation causes an anomalous propagation, that is, the velocity of amplitude maximum appears to be faster than the light velocity. Such a fast propagation is shown to change into the slow propagation characterized by the packet velocity less than the light speed. The new mechanism of the fast propagation is proposed, and the recent experimental results observed on semiconductors with resonant absorption are re-interpreted from this point of view. (Atomindex citation 17:029705)