Analytic Solutions for Initiation of Plasma Absorption above Laser-Irradiated Surfaces;Laser Effects Calculations.

摘要

A program to obtain analytic solutions for the effects of vapor and air absorption,and the subsequent onset of plasma shielding,on the radiation that impinges upon a laser-irradiated surface has been initiated. The problem addressed in this report is the determination of the time scale for ignition of a laser supported absorption wave as a function of laser intensity,material,spot size and wavelength. It is shown that over a range of intensities the vapor properties up to the time for ignition can be calculated by uncoupling the heating from the gas dynamics. The time history of the heating effects is obtained by doing a perturbation upon the flow field. The flow is either one-dimensional planar or two-dimensional axisymmetric depending upon the ratio of an appropriate absorption time scale to a characteristic flow time. (Modified author abstract)