Secure interferometric communications in free space: enhanced sensitivity for propagation in the metre range

N-slit interferometry has recently been applied to generate a series of interferometric characters that propagate, in free space, according to well established interference and optical propagation principles. Any attempt to intercept the interferometric character leads to detectable spatial distortions. Originally, experiments were reported at distances in the centimetre range. Here, successful communications, and enhanced detection sensitivity of optical interception, at distances of over 7 m is reported. Further, we discuss conceptual countermeasures and their inapplicability to intercept, undetected, the interferometric characters.