High-resolution imaging with a two-dimensional resistive anode photon counter

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Abstract
We describe a method for achieving high spatial resolution readout of individual photoelectron events using microchannel plates and a resistive anode. Specifically, we employ a clamped pair of microchannel plates (’’V geometry’’) followed by a gap and a clamped triplet of microchannel plates (’’Z geometry’’) in cascade, in order to achieve a high (3×107) stable electron gain. This high gain in turn allows the position determination of each photoelectron event with a very high signal‐to‐noise ratio, thereby giving a theoretical spatial resolution limited chiefly by the microchannel plate channel spacing rather than by the anode signal‐to‐noise ratio. Our first model of this detector is a windowless vacuum‐ultraviolet image sensor, and demonstrates 500×500 pixel images (50 μm FWHM over a 25‐mm circular field of view). Our spatial resolution is presently limited by the microchannel structure and by the error distribution in our analog pulse ratio electronics. High‐current microchannel plates are employed to avoid serious gain variations with respect to changing count rate. Although our present detector hardware is a demountable assembly for laboratory experimentation, the mount design is compatible with planar, remotely‐processed, proximity‐focused photocathodes, and will shortly be evaluated as a sealed detector for echelle spectroscopy at visible wavelengths.

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