Retrieval of the cross-spectral density propagating in free space

Abstract
A technique for retrieving the cross-spectral density propagating in free space across an arbitrary plane is proposed. Theoretical descriptions are based on the propagation law of the cross-spectral density described in the Fourier domain. Results of an experiment demonstrating retrieval of the cross-spectral density across an arbitrary reference plane are also reported. The cross-spectral density in the observation area is measured by use of a wave-front-folded interferometer, and the retrieved cross-spectral densities and the intensity distribution agree well with the theoretical expectations.