Quantum eciency characterization of LBNL CCD's Part 1: the Quantum Eciency Machine

Instrumentation was developed in 2004 and 2005 to measure the quantum eciency of the Lawrence Berkeley National Lab (LBNL) total-depletion CCD's, intended for astronomy and space applications. This paper de-scribes 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 dicult, but since only ux ratios matter this is not critical. Between the light source and an Oriel MS257 monochromator are a shutter and two lter wheels. High-bandpass and low-bandpass lter 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 C. The ratio of the CCD and in-dewar reference PD signals provides the QE measurement. Additional cross-calibration to a PD on the integrating sphere permits lower-intensity exposures