Anomalous diffraction of a grazing laser beam by a dielectric interface: experimental observation

Abstract

In 1977, Kolomeev et al.1 reported observation of anomalous diffusion of a laser beam when incident at a grazing angle to one surface from the 90° vertex and perpendicular to the other surface of a glass right-angle prism. They also provided a theory for the phenomenon. The diffracted light showed a distinct oscillatory distribution, followed the critical angle of total internal reflection with good directivity, and was due to the interface only. Recently we reexamined the phenomenon and thought that the diffraction effect could serve as the basis for designing optical switches, especially in conjunction with nonlaser optical interfaces. Using a CCD linear detector array, we measured the intensity patterns of the transmitted and the diffracted beams of the following light sources: (a) a single-line He–Ne laser; (a) a dual-line Ar+laser; and (c) a broadband xenon-arc lamp, at both glass–air and water–air interfaces. The optical beams, both inside and outside the prism, were visualized. The fact that the diffraction is due to the interface alone was firmly established by perturbing the interface with films of alcohol, contacting dielectric wedges and metal surfaces, and oscillating wires. All these new results are presented. Comparison to the theory is given, and application of this effect to optical switching is described.