Quasiparticle description of pulse propagation in a lossy dispersive medium

It has been known from extensive saddle point analysis that pulses propagating in a lossy dispersive Lorentzian medium exhibit a high frequency forerunner and frequency chirping. The quasiparticle approximation permits an accurate and numerically efficient calculation of the forerunner frequency chirping with a simple physical explanation. For the case of a Gaussian incident pulse, the error in the second order quasiparticle approximation becomes smaller as the pulse propagates; hence one may apply the quasiparticle method for a wide range of propagation distances with error estimates that can be readily calculated.