Accurate description of optical precursors and their relation to weakfield coherent optical transients
Abstract
We study theoretically the propagation of a stepmodulated optical field as it passes through a dispersive dielectric made up of a dilute collection of oscillators characterized by a single narrowband resonance. The propagated field is given in terms of an integral of a Fourier type, which cannot be evaluated even for simple models of the dispersive dielectric. The fact that the oscillators have a low number density (dilute medium) and have a narrowband resonance allows us to simplify the integrand. In this case, the integral can be evaluated exactly, although it is not possible using this method to separate out the transient part of the propagated field known as optical precursors. We also use an asymptotic method (saddlepoint method) to evaluate the integral. The contributions to the integral related to the saddlepoints of the integrand give rise to the optical precursors. We obtain analytic expressions for the precursor fields and the domain over which the asymptotic method is valid. When combined to obtain the total transient field, we find that the agreement between the solutions obtained by the asymptotic and the exact methods is excellent. Our results demonstrate that precursors can persist for many nanoseconds and the chirp in the instantaneous frequency of the precursors can manifest itself in beats in the transmitted intensity. Our work strongly suggests that precursors have been observed in many previous experiments.
 Publication:

arXiv eprints
 Pub Date:
 May 2007
 arXiv:
 arXiv:0705.4238
 Bibcode:
 2007arXiv0705.4238L
 Keywords:

 Physics  Optics;
 Physics  Classical Physics;
 Physics  Medical Physics
 EPrint:
 11 pages, 4 figures