Absolute quantum efficiency calibration of the AXAF high resolution camera

We discuss the current status of the Advanced X-ray Astrophysics Facility (AXAF) High Resolution Camera (HRC) quantum efficiency (QE) calibration. The absolute quantum efficiency of flight candidate, CsI coated HRC microchannel plates (MCPs) for the imaging detector (HRC-I) manufactured by Galileo Electro-Optics Corporation (GEOC) has been measured at several energies. We find the absolute QE of these MCPs (measured at SAO to be 0.41 at C K-alpha (E=277 eV) and 0.28 at Al K-alpha (E=1487 eV). The absolute QE of flight-like HRC-I MCPs manufactured by Phillips Components (measured at the University of Leicester) is similar to 0.40 at both C K-alpha and Si K-alpha (E=1739 eV). We are now in the process of measuring the absolute QE of both the HRC-I and HRC-S flight detectors at 22 different energies at 4 azimuthal and 5 polar angles. A summary of planned measurements is presented. In addition, we present data taken at the Daresbury Synchrotron Radiation Source to map out the detailed edge structure of the MCP glass and coatings. In particular, we present measurements of the relative QE of CsI coated MCPs around the Cs and I M edges, and absolute measurements around the K K and Cs L(III) edges. The absolute measurements of the flight instrument at the 22 discrete energies will be combined with the relative synchrotron measurements of flight-like detectors to produce the absolute QE of the HRC over the entire AXAF bandpass (0.1 to 10 keV).