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 sub-Rayleigh resolution by scanning a focused beam-in an arbitrary, object-covering pattern that is unknown to the imager-and using N-photon photodetection implemented with a single-photon avalanche detector array. Experiments show resolution improvement by a factor similar to(N - (N) over bar (max))(1/2) beyond the Rayleigh bound, where (N) over bar (max) is the maximum average detected photon number in the image, in good agreement with theory.