X-ray laser radiography of perturbations due to imprint of laser speckle in 0.35 mu m laser irradiation of a thin Si foil

A gain saturated yttrium x-ray laser operating at a wavelength of 15.5 nm has been used as an extreme ultraviolet probe to measure optical depth modulations in a thin Si foil by face-on radiography. The high brightness of this Ne-like x-ray laser allows probing of a sample with a high opacity. This technique is sensitive to very small modulations in the optical depth of the foil, corresponding to thickness variations of a few 10 nm of cold material. This technique is used to measure the effect of direct drive laser imprint on a thin Si foil by face-on radiography using multilayer optics to image the foil with 26x magnification. We have recorded modulations in a thin Si foil that was irradiated by a 400 ps, 0.35 mu m beam at an intensity of about 3x10(12) W/cm(2). (C) 1996 American Institute of Physics.