University of Toronto
Physics Department
Quantum Optics and Condensed Matter

MONDAY SEMINAR

Abstract

Debye shielding is one of the really basic concepts in plasma  physics, having implications wherever free charges appear:  all  through solid-state physics, solar physics, astrophysics, and many  other fields.  Because it describes the way that free charges  self-consistently assemble around a charge perturbation, such as an ion, Debye shielding affects the energy and lineshape of spectral emission and absorption lines, and a host of collective nonlinear phenomena in plasmas, such as stimulated Raman scattering, Brillouin scattering and Thomson scattering, among others.

But when is Debye shielding not Debye shielding?  In ultra-intense  laser-matter interaction studies we have made, we've found a  threshold past which the electromagnetic field of light competes with the electrostatic shielding of Debye electrons in a plasma — past this point, the laser field can actually inhibit Debye shielding, as  it sends shielding electrons off on another 'errand'.

One of the main results is a rearrangement of the fundamental  dispersion relations for waves in plasma.  Ion-acoustic waves (in  which ion perturbations are 'dressed' by Debye electrons) become naked ion-plasma waves, with a different restoring force and frequency, and so the relations for many nonlinear wave couplings are  dramatically changed.  I'll describe some of the basic theory, and show new red- and blue-shifted Stokes-like satellites to high-order laser-harmonics we've discovered in such interactions, and survey  several similar problematic observations in intense laser-plasma interactions, which seem now to make sense.
 
 

Local Host:  Aephraim Steinberg (416-978-0713)

See   http://www.physics.utoronto.ca/~qocmp