Measurements of 4–10 keV x-ray production with the Z-Beamlet laser

In order to characterize the current backlighting capability of Sandia’s Z-Beamlet laser (ZBL) over a range of high photon energies, we measured the x-ray conversion efficiency of the focused 527 nm ZBL beam into 4–10 keV x rays from He-like emission of the elements Sc through Ge (excluding Ga). The measurements approximated ZBL’s nominal backlighting geometry and laser performance at Sandia’s Z soft x-ray facility by irradiating planar foil targets several microns thick rotated 30° to the laser beam axis with a 600 ps pulse at 1 TW. The focal spot diameter was about 150 μm. This study includes measurements of the K-shell x-ray spectrum, x-ray power, and x-ray spot size with an array of filtered high-bandwidth silicon diodes, a convex LiF crystal spectrometer, step wedge filtered x-ray film, and a filtered x-ray pinhole camera. We found agreement with previous work for comparable laser parameters and recorded decreasing conversion efficiency versus atomic number and He-like photon energy.