JOURNAL OF X-RAY SCIENCE AND TECHNOLOGY 5, 73-87 (1995) Monochromatic Backlighting as a Laser-Fusion Diagnostic B. YAAKOBI, F. J. MARSHALL, Q. Su, AND R. EPSTEIN Laboratory for Laser Energetics. University of Rochester. 250 East River Road. Rochestel; New York 14623-1299 Received December 17, 1993: revised June 13, 1994 The case of an x-ray radiographed (backlit) image of a CH-shell laser-fusion target to be imploded by the Omega Upgrade laser system is studied. The goal is to obtain information on the conditions at peak compression, where the experimental constraints due to target self-emission and required spatial resolution are maximal. Particular attention is devoted to the problem of discriminating against the target self-emission. It is shown that a way to selectively image the target with radiation from a backlight source is to obtain a mono- chromatic image at a single spectral line emitted by the backlighter. Two experimental configurations are discussed: (a) an x-ray microscope with a fiat crystal monochromator. and (b) pinhole imaging in conjunction with a curved crystal monochromator. Useful images are obtained with simple CH-shell targets and without the need for a short-pulse backlighter beam. © 1995 Academic Press, Inc. I. INTRODUCTION The method of x-ray backlighting offers some important advantages over methods employing target emission for the study of compression and stability of laser-imploded targets. An important ingredient in the backlighting schemes, as discussed below, is two-dimensional monochromatic imaging; this added feature can likewise be applied to, and enhance, methods based on target self-emission. Monochromatic imaging can be used to probe a particular layer in the target, which contains a suitable element (dopant). The imaging then involves a particular atomic transition of that element that gives rise to either monochromatic emission or absorption. However, as we show below in the case of backlighting, monochromatic imaging must be used even in the absence of a doped layer to overcome the background due to target emission. An advantage of monochromatic backlighting over broadband imaging methods is the potential ability to delineate the interface between the pusher and the fuel. This capability is more easily realized if the compressed fuel is relatively cold near the interface (i.e., a temperature gradient exists in the fuel). Such information can, in principle, provide a direct measure of compression and evidence of any shell distortion. Emission methods can only delineate the hot core, which may consist of the fuel as well as an indeterminate section of the pusher. Monochromatic emission methods can provide this information using doping, but backlighting may have the ability to image the interface even without any target dopant. An additional advantage is the ability to choose a short-enough backlighting wavelength (say, ~, < 3 A) to avoid too 73 0895-3996/95 $6.00 Copyright © 1995 by Academic Press, Inc. All rights of reproduction in any form reserved.