Sub-Rayleigh Imaging via N-Photon Detection

The Rayleigh diffraction bound sets the minimum separation for two point objects to be distinguishable in a conventional imaging system. We demonstrate resolution enhancement beyond the Rayleigh bound using random scanning of a highly-focused beam and N-photon photodetection implemented with a single-photon avalanche detector array. Experimental results show resolution improvement by a factor ~sqrt(N) beyond the Rayleigh bound, in good agreement with theory.