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Position Sensitive Detectors for the Proposed AXAF Imaging Optical/UV Monitor (AXIOM)

We describe the imaging detectors of the AXIOM instrument proposed for NASA's Advanced X-ray Astrophysics Facility (AXAF). The instrument is aligned with the X-ray telescope and consists of a diffraction limited, 30-cm aperture, telescope with redundant position sensitive detectors at the focus. This allows simultaneous imaging at optical and near UV wavelengths of the X-ray target objects. The proposed detectors cover a field of view of 8.5 × 8.5 arcmin2 with a resolution of 1 arcsec (= 50 ¿m FWHM). The quantum efficiency peaks at 30% and exceeds 10% over the wavelength range 125 to 540 nm. The detector design consists of a bi-alkali photocathode on a UV-transmitting window, proximity focussed onto a microchannel plate intensifier with a wedge and strip readout system, and is optimised for high count rates both from point sources and from the sky background.