Submicrometer photoresponse mapping of nanowire superconducting single-photon detectors

We report on the photoresponse mapping of nanowire superconducting single-photon detectors using a focal spot significantly smaller than the device area (10×10μm2). Using a confocal microscope configuration and solid immersion lens, we achieve a spot size of 320nm full width at half maximum onto the device at 470nm wavelength. We compare the response maps of two devices: The higher detection efficiency device gives a uniform response, whereas the lower detection efficiency device is limited by a single defect or constriction.