Precision quantum efficiency measurements on 1.7 micron near infrared devices

High detector quantum efficiency (QE) can greatly improve speed and performance of wide field instruments that strive for fast precision photometry. SNAP, a proposed satellite mission dedicated to exploring the nature of the dark energy will employ a very large focal plane instrumented with about equal number of CCD and NIR sensors totaling more than 600 million pixels covering roughly 0.7 square degrees on the sky. To precisely characterize the NIR detector QE, the SNAP project has put in place a test set-up capable of measuring absolute QE at the 5% level with the goal of ultimately reaching a precision better than 2%. Illumination of the NIR detectors is provided by either a quartz tungsten halogen lamp combined with a set of narrow band filters or a manually tunable monochromator. The two light sources feed an integrating sphere at a distance of roughly 60 cm from the detector to be tested and a calibrated InGaAs photodiode, mounted adjacent to the NIR detector provides absolute photon flux measurements. This paper describes instrumentation, performance and measurement procedures and summarizes results of detailed characterization of the QE on several SNAP devices as a function of wavelength.