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

Abstract

In high flux (1013–15 W/cm2) laser-plasma interaction, a large part of the incoming laser energy is radiated into soft x-rays. To determine both the shape of this spectrum and the conversion efficiency, we have designed and 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 (French 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’utilisation du Rayonnement Electromagnétique (LURE) in Orsay. The initial version of this instrument was first successfully implemented on laser plasmas experiments at the Phébus facility in France and an improved version is now operating 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 with the coaxial diode response to improve hard x-ray rejection. Intermediate energy channels (1.5 keV<hν<5 keV) used only a filter and coaxial diode. For the hardest channels (>5 keV) we replace the x-ray diode (not sufficiently sensitive) with a photoconductive detector (neutron-damaged GaAs). An equivalent instrument will be designed for the future National Ignition Facility (NIF) in the United States and the Laser Mégajoule (LMJ) in France.

X-ray diagnostic calibration with the tabletop laser facility EQUINOX

“…For instance, let us consider an x-ray diode used in the broad band spectrometer DMX. 16 Spectral sensitivity of one x-ray diode depends on the chemical composition of the photocathode surface. [17][18][19] It is linearly related to the absorption coefficients of its surface constituents: aluminum, carbon, and oxygen.…”

Métrologie autour d'installations plasma-laser. Utilisation du rayonnement synchrotron

“…Dans ce cas, on mesure la quantité d'énergie émise par échantillonnage, c'est-à-dire dans un ensemble de tranches d'énergie AE centrées sur une énergie E. Le spectre est ensuite reconstitué avec un pouvoir de résolution de quelques unités. La conception et la réalisation par B. Villette en 1997 [3], d'un nouveau spectromètre nommé DEMIXART (Dispositif d'Etude de L'Emission X Avec Résolution Temporelle) nous ont fait avancer notablement dans cette spectrométrie. Le diagnostic est composé de 15 voies indépendantes réparties sur une gamme spectrale s'étalant de 0,1 à 5 keV.…”

Characterization and error analysis of anN×Nunfolding procedure applied to filtered, photoelectric x-ray detector arrays. II. Error analysis and generalization

“…Line spectra produce unfold values remote to the location E of each line and are strongly dependent on E : the passband functions also predict bin-to-bin unfold oscillations for certain line spectra, as previously noted [57,60], and complicated flux averaging for continuum spectra with superposed prominent emission lines. (Background channels mitigate these effects [47,61,62] by subtracting out the nettlesome lines.) Significantly broadened spectra distort the unfold reconstruction at high x-ray energies: the passband functions bound such distortions.…”