N-slit interferometer for secure free-space optical communications: 527 m intra interferometric path length

The N-slit interferometer is demonstrated to function with an intra interferometric propagation path length of 527.33 m. Interferograms representing several interferometric characters, corresponding to N = 2, 3, 4, and 5, were recorded at the interferometric plane located at the end of an open air propagation range. Interferometric computations, based on the application of Dirac's notation, were successfully used to predict the structure and divergence of the propagating interferograms. These measurements were carried out during an unusual mild-temperature, low-humidity, summer night in northern Alabama. In the laboratory, at an intra interferometric propagation path length of 7.235 m, the N-slit interferometer was also used to successfully detect the intrusion of microscopic fibers into the intra interferometric propagation path. These experiments led to the detection of diffraction patterns superimposed over the interferograms.