Diffraction controlled backscattering threshold and application to Raman gap
Abstract
The range of stimulated Raman scattering (SRS) frequencies covers a domain which at the low end abuts half the laser frequency, omega_0 / 2, according to the simplest SRS theories, corresponding to scatter from electron densities near 1/4 critical. Experiments, on the other hand, clearly point to a frequency gap: SRS is not observed at frequencies close to and above omega_0 / 2, indicating a drastic disruption of scatter from Langmuir waves as electron densities approaches 1/4 critical from below. Several one-dimensional mechanisms, linear and nonlinear, have been proposed to explain this "Raman gap". In this paper we release the one-dimensional constraint by allowing diffraction of the scattered light. In the linear convective regime we find that diffractive effects on SRS from a wide speckled laser beam tend to increase the SRS threshold with increase of density, so long as the interaction length is comparable to or larger than a speckle length. This may lead to a new, diffraction controlled, contribution to the Raman gap.
Cite
@article{arxiv.1011.5211,
title = {Diffraction controlled backscattering threshold and application to Raman gap},
author = {Harvey A. Rose and Philippe Mounaix},
journal= {arXiv preprint arXiv:1011.5211},
year = {2015}
}