A model of high resolution cross strip readout for photon and ion counting imaging detectors

Recent advances in the photon counting, imaging readout for microchannel plate (MCP) detectors has led to a substantial improvement in their spatial resolution. The spatial accuracy (~7-10 mum) of an MCP detector with a cross strip readout has been shown to be limited by the MCP pore size (<10 mum). In this paper we study the ultimate resolution limits of the cross strip readout itself. The model allows us to determine the requirements on the anode´s geometry and the signal processing electronics in order to reach a particular spatial resolution. The optimal detector parameters, such as the width of the charge footprint at the anode (determined by the distance and the field between the MCP and the anode), and the gain of the detector can also be found with the help of our model. The model indicates that the optimum FWHM of the charge footprint distribution at the anode is a factor of ~1.6 larger than the anode period. Given a noise of charge sensitive amplifiers of 350 electrons rms each we predict that the MCP gain can be as low as 2.5times10⁵ for this detector to resolve ~7 mum features. Results of our modeling also indicate that the accuracy of the position obtained for center of gravity centroiding of the charge distribution is inferior to fitting a Gaussian-like analytical function, providing the geometry of the anode is accurate enough. The model predictions are compared with the experimentally measured images and reveal the critical parameters (anode´s geometry accuracy and amplifier noise), which can be improved in future detectors.