We analyze, and test experimentally, a method of imaging at very low light levels using spatial interference between a strong local oscillator field and a weak beam. By using Fourier phase recovery techniques familiar in classical interferometry and by correcting the inhomogeneities in the reference field, we can represent the quadrature components of a given spatial mode in the complex plane. Further, by post selection filtering (convolution and sampling), the method can distinguish photons of different orbital angular momentum with a one-count standard deviation consistent with the quantum noise floor.
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