Absolute calibration of the spectral sensitivity of an x-ray streak camera over the 0.1-10 keV spectral range equipped with CsI photocathode

In this paper, we report the absolute measurement of the spectral sensitivity of a bilamellar tube x-ray streak camera (XRSC) over the 0.1-10 keV range equipped with a CsI photocathode for Laser MegaJoule (LMJ) fusion experiments. This calibration of the XRSC is performed in static mode by using two multi-anode x-ray generators. Two silicon drift detectors (SDDs) previously calibrated at the Physikalisch-Technische-Bundesanstalt radiometric laboratory are used as secondary standards. Both x-ray generators work with a specific monochromator for radiometric measurements. In the sub-keV region, a 1 m-grazing incidence Rowland geometry monochromator specifically developed to handle LMJ's x-ray camera is used, whereas for higher energies (>2 keV), a double-crystal monochromator is employed. The absolute spectral sensitivity of the XRSC is obtained by comparing the CCD counts of the XRSC output with the output counts in x-ray lines recorded by the SDD. The results obtained below 1.2 keV are, to our knowledge, the first measurements of the spectral sensitivity of an XRSC in the soft x-ray range with a CsI photocathode. Comparison with a model describing the spectral dependence of the sensitivity of the XRSC revealed that measurements obtained in the sub-keV region are greater than expected, whereas they agree with the model above 4.5 keV. There may be several contributors to this behavior, including the grain morphology of the CsI layer and exposure to air.