The diffraction effects produced by light incident upon an interface at the critical angle of total reflection are examined for the purpose of explaining the weak illumination recently detected by Acloque and Guillemet, and by Osterberg and Smith. This illumination accompanies the rays reflected from the interface, but it occurs in a manner that cannot be interpreted in conventional geometric-optical terms. We show that a rigorous but simple approach that accounts for first-order-diffraction effects is capable of explaining the experimental results in terms of a lateral wave which in fact may provide the dominant field under certain circumstances. In particular, we examine the special case of a collimated light beam and show that the lateral wave is strongest, and accounts for the observed illumination, when the beam is incident at the critical angle of total reflection. The quasi-optical properties of this wave are emphasized and they are shown to provide straightforward physical interpretations for the various features of the weak-illumination field.
© 1969 Optical Society of America
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