EXTREME-ULTRAVIOLET PROBING OF LASER IMPRINT IN A THIN FOIL USING AN X-RAY LASER BACKLIGHTER

For direct drive inertial confinement fusion, a capsule is imploded by directly illuminating the surface with laser light. Beam smoothing an d uniformity of illumination affect the seeding of instabilities at th e ablation front. We have developed a technique for studying the impri nt of a laser beam on a thin foil using an x-ray laser as an extreme u ltraviolet (XUV) backlighter. We use multilayer XUV optics to relay th e x-ray laser onto the directly driven foil, and then to image the foi l modulation onto a charged coupled device camera. This technique allo ws us to measure small fractional variations in the foil thickness. We have measured the modulation due to imprint from a low intensity 0.35 mu m drive beam incident on a 3 mu m Si foil using an yttrium x-ray l aser on Nova. We present results from a similar technique to measure t he imprinted modulation due to a low intensity 0.53 mu m drive beam in cident on a 2 mu m Al foil using a germanium x-ray laser at the Vulcan facility. (C) 1997 American Institute of Physics.