The Nonlinear Optics of Plasmas

It is well known that plasmas exhibit many of the characteristics of a non-linear optical medium when intense electromagnetic waves are incident upon it. These include harmonic generation, simulated Brillouin and Raman scattering, degenerate and resonant four wave mixing, self-focusing and parametric amplification. In addition, plasmas demonstrate certain unique nonlinear phenomena such as nonlinear mode conversion, two plasmon decay and relativistic self-focusing. The nonlinear optics of plasmas is therefore at once both challenging and rich for an experimentalist. It is challenging because many of the nonlinear optical phenomena occur simultaneously in a plasma. Also, when the plasma modes, characteristic of many of these instabilities, become large, kinetic effects and wave-wave interactions become extremely important. On the other hand, the plasma medium can be directly probed using coherent Thomson scattering technique revealing the richness of the physics. Experiments carried out by the author and his collaborators over the past decade are summarized and future directions for this field outlined in this paper.