Quasiparticle description of wave propagation and reflection in inhomogeneous media

Quasiparticle description of wave propagation and reflection from a transversely and/or longitudinally inhomogenous medium have been investigated. For a transversely inhomogeneous medium the first order quasiparticle method for wave propagation in the parabolic approximation has been extended to wide angle propagation and displays very good accuracy in the parameter range where dielectric and beam widths are of the order or larger than a wavelength. Rapid transverse variation is treated by an integrodifferential equation including higher order perturbations. Wave reflection from longitudinally as well as transversely inhomogeneous media is described in terms of quasiparticle reflection. Quasiparticle reflection probabilities, determined from the medium profile as a function of position and momentum, are introduced for separable media, i.e., , to explain wave coupling of incident and reflected waves. Within the quasiparticle theory the interpretation of quasiparticle reflection is self-consistently derived from the wave equations and the definition of a quasiparticle distribution function. The interpretation is applicable for relatively small longitudinal scales and includes the case of a mismatched open dielectric waveguide junction.