Spectral response calibrations of x-ray diode photocathodes in the 50-5900eV photon energy region

X-ray diode photocathodes are employed in diagnostic instruments on the Hel en laser at the Atomic Weapons Establishment (AWE) Aldermaston, UK. The pho tocathodes are mainly used in the Dante fast diode array and flat response diodes. These diagnostics enable the soft x-ray spectral emissions of laser irradiated targets to be determined. To derive quantitative spectral infor mation, the quantum efficiency of the photocathodes must be known over the range of x-ray energies of interest. The photocathodes were manufactured in 1982, and were initially calibrated at that time. Since then further measu rements have been performed in 1988 and 1999. The photocathodes have been e xposed to a wide range of conditions during their lives, ranging from use i n experiments to storage in a dry nitrogen environment. Reported here are t he results of calibrations performed in 1999 at the soft x-ray calibration facility EXCALIBUR at AWE, Aldermaston, and at the National Synchrotron Lig ht Source in Brookhaven NY. An assessment of their current condition and an evaluation of the change in their response over time, and the possible rea sons for these changes, are made. (C) 2001 American Institute of Physics.