Precession of wave packets in smoothly inhomogeneous dispersive media

In the quasi-optical aberration-free approximation, a parabolic equation for the envelope of an electromagnetic wave packet propagating along the geometric optical ray in a smoothly inhomogeneous isotropic medium with time dispersion is obtained. The effects of the combined influence of the refraction, diffraction, and dispersion on the evolution of the packet are analyzed; in particular, the effects that cause the precession of the envelope waves about the binormal to the propagation trajectory are considered.