Imaging with the invisible light

We describe a UV photo-detector with single photon(electron) counting and imaging capability. It is based on a CsI photocathode, a GEM charge multiplier and a self triggering CMOS analog pixel chip with 105k pixels at 50 micron pitch. The single photoelectron produced by the absorption of a UV photon is drifted to and multiplied inside a single GEM hole. The coordinates of the GEM avalanche are reconstructed with high accuracy (4 micron rms) by the pixel chip. As a result the map of the GEM holes, arranged on a triangular pattern at 50micron pitch, is finely imaged.