Characterizing subpixel spatial resolution of a hybrid CMOS detector

Soft X-rays (0.1 to 10 keV) will liberate between tens and thousands of electrons from the absorber array of a depleted silicon detector. These electrons tend to diffuse outward into what is referred to as the charge cloud, which is then picked up by several pixels and forms a specific pattern based on the exact incident location of the X-ray. By performing the first ever application of a "mesh experiment" on a hybrid CMOS detector (HCD), we have experimentally determined the charge cloud shape and used it to perform subpixel localization of incident X-rays on a photon-by-photon basis for a custom 36-μm pixel pitch H2RG HCD. We find that significant spatial resolution improvement is possible for all events, with 68% confidence regions equal to 7.1 × 7.1, 0.4 × 7.1, and 0.4 × 0.4 μm for 1-pixel, 2-pixel, and 3-to 4-pixel events, respectively. This represents a much finer resolution than that provided by containment within a single pixel.