INTERACTION OF LASER-ABLATION PLASMA PLUME WITH GRID SCREENS

Optical emission spectroscopy and charge collector time-of-flight meas urements have been used to study interaction of laser ablation carbon plasma with grid screens in vacuum under conditions typical for pulsed laser deposition of thin diamondlike films. The effect of velocity di stribution transformation of the ion, flow has been observed and studi ed in a variety of experimental conditions. Our results indicate that the observed phenomenon is due to interaction of two plasma flows, the initial expanding one and the fraction of that flow scattered by the substrate or the screen. Three typical modes of velocity distribution function transformation have been observed depending on the plasma den sity: linear attenuation of the flow density, nonlinear attenuation of the slow ''tail'' of the velocity distribution function, and nonlinea r transformation of the entire velocity spectrum. The latter regime oc curs when plasma is throttling through the fine mesh screen. Our obser vations show that the reported phenomenon may substantially affect dep osited him properties. (C) 1995 American Institute of Physics.