Self-calibration of a thinned, backside illuminated charge coupled devices in the soft x-ray region

Abstract

A semiempirical method of calibrating a thinned, backside illuminated charge coupled device (CCD) chip in the soft x-ray region is presented. It is based on determining the thickness of the dead layer self-consistently using the continuum emission from laser produced plasmas. The CCD camera system was coupled to a transmission grating spectrometer and recorded the spectrally resolved continuum emission from laser irradiated tungsten targets. The thickness of the dead layer was then determined by comparing the experimental spectra with the calculated quantum efficiency for a thinned CCD using a simplified model. In this way the CCD chip was semiempirically calibrated. The accuracy of the calibration in the soft x-ray range was assessed by comparing the CCD recorded spectra with those recorded by a spectrometer using the absolutely calibrated Kodak 101 photographic plates and a similar transmission grating. Based on this calibration, the CCD sensitivity is deduced to be about two orders of magnitude higher than that of the Kodak plates in this wavelength range.