Second harmonic generation in a laser plasma (review)

A review is given of experiments carried out to date on the generation of laser radiation frequency harmonics in a plasma on exposure to neodymium, ruby, and CO₂ lasers. A physical picture of second harmonic generation in a laser plasma is developed on the basis of an analysis of theoretical and experimental investigations. Experiments involving the spherical irradiation of solid targets carried out in the Kal'mar laser system made it possible to identify for the first time the processes taking place in the critical-density plasma region under conditions as close as possible to "thermonuclear". New methods are proposed for ultrafast diagnostics of a transient superdense plasma using the second harmonic radiation spectrum.