A dual-channel, curved-crystal spectrograph for petawatt laser, x-ray backlighter source studies

A dual-channel, curved-crystal spectrograph was designed to measure time-integrated x-ray spectra in the approximately 1.5 to 2 keV range (6.2-8.2 A wavelength) from small-mass, thin-foil targets irradiated by the VULCAN petawatt laser focused up to 4x10(20) W/cm(2). The spectrograph consists of two cylindrically curved potassium-acid-phthalate crystals bent in the meridional plane to increase the spectral range by a factor of approximately 10 compared to a flat crystal. The device acquires single-shot x-ray spectra with good signal-to-background ratios in the hard x-ray background environment of petawatt laser-plasma interactions. The peak spectral energies of the aluminum He(alpha) and Ly(alpha) resonance lines were approximately 1.8 and approximately 1.0 mJ/eV sr (approximately 0.4 and 0.25 J/A sr), respectively, for 220 J, 10 ps laser irradiation.