Measurement of the spatial coherence of CO2 laser radiation by the frequency up-conversion method

A polarizing interferometer and a photomultiplier operated as a photon counter were used in measurements of the spatial correlation function of the radiation field of a CO₂ laser, which was up-converted from the infrared range in a proustite crystal. The proposed method made it possible to use a low-power He–Ne laser as a pump source in parametric conversion and to make high-precision measurements.