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

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Abstract
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 26× magnification. We have recorded modulations in a thin Si foil that was irradiated by a 400 ps, 0.35 μm beam at an intensity of about 3×1012 W/cm2.