Multiphoton optical heterodyne detection

After reviewing recent work on multiphoton direct detection and single-photon heterodyne detection, we examine the behavior of a multiphoton absorption heterodyne receiver. Expressions are obtained for the detector response, signal-to-noise ratio (SNR), and minimum detectable power for a number of cases of interest. Receiver performance is found to depend on the higher order correlation functions of the radiation field and on the local oscillator (LO) irradiance. Although performance similar to that of the single-photon heterodyne receiver can theoretically be achieved, practical problems would appear to make this difficult. A physical interpretation of the process in terms of the absorption of monochromatic and nonmonochromatic photons is given. The double-quantum case is treated in particular detail; the results of a preliminary experiment are presented and suggestions for future experiments are provided.