MICRO‐FRESNEL STRUCTURES FOR MICROSCOPY OF LASER GENERATED BRIGHT X‐RAY SOURCES*

Abstract

A brief parametric survey of the x-ray characteristics of a gold micro-disk irradiated at 3 x 10/sup 14/ watt/cm/sup 2/ by a 1 nsec Nd-glass laser pulse has been provided as an example of a laser generated bright x-ray source. It was shown that a simple phenomenological model of the laser generated x-ray source as a microscopic equilibrium plasma radiating as a blackbody for a finite time determined by its hydrodynamic disassembly and radiation losses, serves to provide an adequate approximation to the x-ray characteristics of such sources. The current state of x-ray microscopy within the LLL laser fusion program was briefly reviewed. Kirpatrick--Baez grazing incidence reflection x-ray microscopes are being used to provide 3 to 5 ..mu..m resolution, broadband images (..delta..E/E approx. 0.3) over a spectral range from .6 keV to 3.5 keV. Zone Plate Coded Imaging is used to provide 5 to 10 ..mu..m resolution, broadband (..delta..E/E approx. 0.5) images over a spectral range from 3 keV to 50 keV. Efficient x-ray lensing elements with anticipated submicron resolution are being developed for narrowband (..delta..E/E approx. 10/sup -2/) imaging applications over a spectral range .1 keV to 8 keV. The x-ray lens design is that of a transmission blazedmore » Fresnel phase plate. Micro--Fresnel zone plates with 3200 A minimum linewidth have been fabricated and preliminary resolution tests begun. The first resolution test pattern, having minimum linewidth of 2.5 ..mu..m, was imaged in lambda = 8.34 A light with no difficulty. Newer test patterns with submicron minimum line are being prepared for the next stage of resolution testing. An off-axis Fresnel zone plate with 1600 A minimum linewidth is presently being fabricated for use as an imaging spectrometer in order to provide spatially separated, chromatically distinct images of characteristic line emissions from laser fusion targets.« less