DOUBLE-LAYER EFFECTS CAUSING NEARLY UNIFORM STRIATED 2ND HARMONIC EMISSION FROM A LASER IRRADIATED PLASMA CORONA

The uniform side-on emission of second harmonic radiation has recently been measured from the corona of a laser irradiated plasma with large electron density gradients. A theoretical model has been developed to study the internal electric fields and double layers in such strongly inhomogeneous plasmas. The analytical model shows immediately a density-independent second harmonic term which reproduces very closely the measured intensity of the second harmonic. A detailed numerical evaluation of the term, for a plasma with a linear density profile (permitting Airy solutions), results in a net intensity with small spatial variation but also with both long and short wavelength periodicities exactly as measured. The observed vanishing of the periodicity, when broad band laser sources are used, can then immediately be explained from integration of the standing-wave like oscillations. © 1990, Cambridge University Press. All rights reserved.