Explanation of the widespread uniform second harmonic emission with spatial periodicity from laser irradiated fusion pellets

A new macroscopic model for laser-plasma interaction without space charge neutrality permits the study of electric fields and double layers. The results show the generation of large amplitude longitudinal oscillations driven by the laser field. The oscillation field consists of eight terms, including the typical collisionally damped ambipolar field, and two second harmonic (2ω) terms. The focus of the paper is one of the 2ω terms which describes the nearly density independent generation of second harmonics throughout the whole plasma corona. The results presented are shown to be in agreement with recent observations of widespread quasi-uniform second harmonic emission from laser irradiated targets, and include the automatic reproduction of the observed spatial periodicities. (author). 12 refs, 2 figs