Developments in imaging devices for microchannel plate detectors

Microchannel plate (MCP) photon counting detectors using image readout devices such as the Vernier and Cross-strip anodes can now achieve spatial resolutions limited by the pore geometry of commercially available MCPs. We describe progress in the development of a new readout system, part of our program to achieve MCP limited spatial resolution and larger format sizes using the small pore MCPs. We discuss the limitations of charge division devices that require high precision charge measurement and present a readout technique using charge comparison, with the potential to achieve large format readouts at high count rates. This scheme use a technique whereby the position coordinate of an event is represented by the order of amplitudes of a set of electrodes. Each coordinate is identified by a unique permutation of electrodes and is determined by comparing the charge collected on the electrodes. One of the major advantages offered by this scheme is a much lower signal-to-noise requirement. This will allow the detector to operate at substantially lower gain, raising the MCP limited count rate threshold. We present a simple and practical readout design to implement the charge comparison scheme, which uses the image charge technique to enhance performance in the areas of spatial resolution, linearity and image stability. The high count rate capability of the new design is augmented by an ability to capture events in parallel without the requirement for excessive numbers of electronic channels. We describe an electronics scheme specifically for the charge comparison readout and discuss how it can provide enhanced spatial resolution by using a charge centroiding technique based on pulse timing information. We support this with timing measurements obtained from a breadboarded electronic channel.