Measuring the soft X-ray quantum efficiency of charge-coupled devices using continuum synchrotron radiation

We have measured the soft X-ray (250-4500 eV) quantum efficiency of a charge-coupled device using continuum synchrotron radiation. The spectrum of the synchrotron radiation can be calculated accurately, so the observed pulse height spectrum is a direct measure of the detector efficiency over the synchrotron bandpass. A key function in modeling the efficiency is the energy dependence of the fraction of detected single pixel events. We find that a model including the effects of charge drift and diffusion plus two different depletion depths (corresponding to the collection and barrier phases under the gates) is required. With this model the absolute QE can be determined to within ∼5% everywhere over the 500 to 4500 eV bandpass.