title: Role of the instantaneous spectrum on pulse propagation in causal linear dielectrics.
abstract: A model-independent theorem demonstrates how a causal linear dielectric medium responds to the instantaneous spectrum, that is, the spectrum of the electric field pulse that is truncated at each new instant (as a given locale in the medium experiences the pulse). This process leads the medium to exchange energy with the front of a pulse differently than with the back as the instantaneous spectrum laps onto or off of nearby resonances. So-called superluminal pulse propagation in either absorbing or amplifying media as well as highly subluminal pulse propagation are understood qualitatively and quantitatively within this context.
authors.affiliation: Department of Physics and Astronomy, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: J
authors.initials: J
authors.lastname: Peatross
authors.forename: M
authors.initials: M
authors.lastname: Ware
authors.forename: S A
authors.initials: SA
authors.lastname: Glasgow