High harmonic generation in high power lasers

This chapter examines the response of a strongly inhomogeneous plasma to a high power laser light as produced by the CO2-laser Gemini and Helios systems. The response is studied in a continuous density gradient and then the generation of high harmonics in the laser produced plasmas is investigated. Fluid theory is used to derive a nonlinear and time-dependent differential equation describing the electron response in Lagrangian coordinates. Topics covered include derivation of the equation of motion, wavebreaking, and high harmonic generation. The fluid response of electrons in a steep density gradient to a p polarized powerful laser light is highly nonlinear. The source of a given high harmonic frequency is localized around the density region corresponding to a local plasma wave at that frequency. The intensity of the radiation coming out of the plasma is evaluated using the numerical results for the nonlinear current density. It is shown that the harmonic production efficiency is very high and the power densities of different harmonic are fairly constant over several harmonics