DMX: An absolutely calibrated time-resolved broadband soft x-ray spectrometer designed for MJ class laser-produced plasmas (invited)

In high flux (10(13-15) W/cm(2)) laser-plasma interaction, a large part of the incoming laser energy is radiated into soft x-rays. To determine both t he shape of this spectrum and the conversion efficiency, we have designed a nd tested an absolutely calibrated broadband soft x-ray spectrometer with a high temporal resolution (100 ps). The detector in this spectrometer is a new coaxial x-ray diode coupled with a fast single shot oscilloscope (Frenc h IN7100 with 7 GHz frequency response cutoff). Both absolute calibrations (x-ray response of diodes) and relative calibrations (filters and mirrors) have used the French synchrotron beam lines at Laboratoire pour l'utilisati on du Rayonnement Electromagnetique (LURE) in Orsay. The initial version of this instrument was first successfully implemented on laser plasmas experi ments at the Phebus facility in France and an improved version is now opera ting at the Omega laser facility in Rochester, New York. The emitted x-ray spectrum is absolutely measured in 18 broad bands from 50 eV up to 20 keV. The softer bands (<1.5 keV) combine mirror and filter responses coupled wit h the coaxial diode response to improve hard x-ray rejection. Intermediate energy channels (1.5 keV <h nu <5 keV) used only a filter and coaxial diode . For the hardest channels (>5 keV) we replace the x-ray diode (not suffici ently sensitive) with a photoconductive detector (neutron-damaged GaAs). An equivalent instrument will be designed for the future National Ignition Fa cility (NIF) in the United States and the Laser Megajoule (LMJ) in France. (C) 2001 American Institute of Physics.