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

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.