The usual quantum efficiency (QE) measurement heavily relies on a calibrated photodiode (PD) and the knowledgeof the CCD s gain. Either can introduce significant systematic errors. But reflectivity can also be used to verify QE measurements. 1 - R >_ QE, where R is the reflectivity, and over a significant wavelength range, 1 - R = QE. An unconventional reflectometer has been developed to make this measurement. R is measured in two steps, using light from the lateral monochromator port via an optical fiber. The beam intensity is measured directly with a PD, then both the PD and CCD are moved so that the optical path length is unchanged and the light reflects once from the CCD; the PD current ratio gives R. Unlike traditional schemes this approach makes only one reflection from the CCD surface. Since the reflectivity of the LBNL CCDs might be as low as 2 percent this increases the signal to noise ratio dramatically. The goal is a 1 percent accuracy. We obtain good agreement between 1 - R and the direct QE results.

Instrumentation was developed in 2004 and 2005 to measure the quantum efficiency of the Lawrence Berkeley National Lab (LBNL)total-depletion CCD's, intended for astronomy and space applications. This paper describes the basic instrument. Although it is conventional even to the parts list, there are important innovations. A xenon arc light source was chosen for its high blue/UV and low red/IR output as compared with a tungsten light. Intensity stabilization has been difficult, but sinceonly flux ratios matter this is not critical. Between the light source andan Oriel MS257 monochromator are a shutter and two filter wheels. High-bandpass and low-bandpass filter pairs isolate the 150-nm wide bands appropriate to the wavelength, thus minimizing scattered light and providing order blocking. Light from the auxiliary port enters a 20-inch optical sphere, and the 4-inch output port is at right angles to the input port. An 80 cm drift space produces near-uniform illumination on the CCD. Next to the cold CCD inside the horizontal dewar is a calibrated reference photodiode which is regulated to the PD calibration temperature, 25$^\circ$ C. The ratio ofthe CCD and in-dewar reference PD signals provides the QE measurement. Additional cross-calibration to a PD on the integrating sphere permitslower-intensity exposures.

We describe charge-coupled device (CCD) development activities at the Lawrence Berkeley National Laboratory (LBNL). Back-illuminated CCDs fabricated on 200-300 mu m thick, fully depleted, high-resistivity silicon substrates are produced in partnership with a commercial CCD foundry.The CCDs are fully depleted by the application of a substrate bias voltage. Spatial resolution considerations require operation of thick, fully depleted CCDs at high substrate bias voltages. We have developed CCDs that are compatible with substrate bias voltages of at least 200V. This improves spatial resolution for a given thickness, and allows for full depletion of thicker CCDs than previously considered. We have demonstrated full depletion of 650-675 mu m thick CCDs, with potential applications in direct x-ray detection. In this work we discuss the issues related to high-voltage operation of fully depleted CCDs, as well as experimental results on high-voltage-compatible CCDs.