2-D X-ray laser-plasma imaging using Bragg Fresnel multilayer zone plates

Two types of Bragg Fresnel multilayer zone plates operating in the keV range have been investigated for X-ray laser-plasma imaging. Elliptical on-axis and off-axis Bragg Fresnel multilayer zone plates were characterised. With the on-axis zone plate all the reflection orders are superposed in the same plane. The image contrast is then degraded as the zone plate focus distance is not the same for all orders. The problem is avoided with an off-axis zone plate with which the different orders in the image plane are spatially separated. The Al Pie, strong emission line (7.757 Angstrom) of a laser produced aluminium plasma has been selected for the imaging tests. The first order reflected intensity has been optimized by varying the Bragg and azimuthal angles. As a result, an X-ray image of a fine gold grid backlighted by the aluminium plasma emission has been obtained with a spatial resolution very close to the theoretical limit of the imaging mounting. (C) 1998 Elsevier Science B.V. All rights reserved.