ABSTRACT
The Herpin theorem permits the reflectance of an arbitrary medium to be reproduced with a substrate of one complex refractive index overlaid with a coating film of a second complex refractive index and an appropriate thickness. The reflectances of a variety of laser-plasma-coupling experiments can be matched with a simple and physically meaningful procedure for choosing the fitting parameters. For short-pulse experiments, s-light coupling is dominated by substrate interactions at electron densities above critical and p-light coupling is dominated by resonance at the critical density. The weak dependence of resonance absorption on damping is the result of the harmonic-oscillator resonance form. As the plasma scale length becomes vanishingly small, the reflectance is that of the Fresnel equations, but surprisingly small plasma scale lengths have dramatic effects on the p-light reflectance. Film-substrate and WKB models predict similar resonance absorption, where both models are valid approximations and both should agree with multilayer and Helmholtz wave-optics calculations. For plasma scale lengths well below a wavelength, the film-substrate and the vacuum-heating models are closely related.
ABSTRACT
Assuming Fresnel absorption for s-polarized light and resonance absorption for p-polarized light provides agreement with the significant features of subpicosecond high-intensity KrF laser-produced plasma experiments. These features include the s- and p-light angular dependence and magnitude of the reflectance. Dramatic differences exist in the threshold for emission of x-ray photons above 0.5 keV, the x-ray emission intensity, and the efficiency for x-ray production by absorbed p and s light. It is shown that resonant p-light absorption occurs at the laser critical density and that the s-light absorption at a higher electron density causes more efficient x-ray production by p light than by s light.
ABSTRACT
Some superficially simple laser-plasma interaction experiments continue to pose perplexing questions in laser-fusion studies. Optical absorptance is an outstanding example. Absorptance is discussed by analyzing experimental results from several laboratories. Resonant absorption explains satisfactorily all shortpulse data obtained to date.
ABSTRACT
By placing a thin layer of a metal with plasma frequency omega(p) upon a substrate of a second metal with a plasma frequency much greater than omega(p) a configuration is created that greatly enhances plasma-resonance effects upon reflectance. Sample results of calculations for films of potassium and silver deposited upon an aluminum substrate are presented. The results suggest that reflectance measurements with such composite samples may provide new information on solid-state plasma resonances as well as provide a simulation for other interactions of electromagnetic radiation with bounded plasmas.
ABSTRACT
The polarization of extreme uv light provided by a normal incidence monochromator used with synchrotron radiation from the 6-GeV electron synchrotron DESY has been measured. The measured polarization increases from 82% at 500 A to 87% at 1000 A, and is in excellent agreement with the calculated polarization of the light incident upon the monochromator grating. A reflecting polarimeter consisting of a polarizer and an analyzer each made of four gold mirrors has been used in the measurement.
