Geometrical optics prohibits any penetration of light into an optically rarer medium in the case of total reflection. When sandwiching, however, the rarer medium between optically denser media, a transmitted beam can be observed in the third medium. The experiment is often realized by a double-prism arrangement [1]; the effect is called frustrated total reflection due to the enforced transmission. Amazingly, the reflected and transmitted beams are shifted with respect to geometrical optics as conjectured by Newton [2] and experimentally confirmed by Goos-Hänchen 250 years later [3]. However, inconsistent results on the spatial shifts have been reported [4-7]. Here we report on measurements of the Goos-Hänchen shift in frustrated total reflection with microwaves. We found an unexpected influence of the beamwidth and angle of incidence on the shift. Our results are not in agreement with both previous experiments [6,7] and theoretical predictions [8-10]. The topic of frustrated total reflection is important for both fundamental research and applications [11-13].
Former QED-based studies of evanescent modes identified these with virtual photons. Recent experimental studies confirmed the resulting predictions about non-locality, non-observability, violation of the Einstein relation and the existence of a commutator of field operators between two space-like separated points. Relativistic causality thus is violated by the near-field phenomenon evanescent modes while primitive causality is untouched.
Tunneling is probably the most important physical process. The observation that particles surmount a high mountain in spite of the fact that they don't have the necessary energy can not be explained by classical physics. However, this so called tunneling became allowed by the theory of quantum mechanics. Experimental tunneling studies with different photonic barriers from microwave frequencies up to ultraviolet frequencies pointed toward a universal tunneling time [1,2]. The observed results and calculations have shown that the tunneling time of opaque photonic barriers (for instance optical mirrors) equals approximately the reciprocal frequency of the electromagnetic wave in question. The tunneling process is described by virtual photons [3]. Virtual particles like photons or electrons are not observable. However, from the theoretical point of view, they represent necessary intermediate states between observable real states. In the case of tunneling there is a virtual particle between the incident and the transmitted particle. Tunneling modes have a purely imaginary wave number. They represent solutions of the Schrödinger equation and of the classical Helmholtz equation. The most prominent example of the occurrence of tunneling modes in optics is frustrated total internal reflection (FTIR) at double prisms. In 1949 Sommerfeld [4] pointed out that this pseudo classical optical phenomenon represents the analogy of quantum mechanical tunneling. Recent experimental and theoretical data confirmed the conjecture that the tunneling process is characterized by a universal tunneling time independent of the kind of field. Tunneling proceeds at a time of the order of magnitude of the reciprocal frequency of the wave.Optical evanescent modes and solutions of quantum mechanical tunneling have a purely imaginary wave number. This means that they do not experience a phase shift in traversing space. The delay time τ of a propagating wave packet is given by the derivative τ = −dφ/dω,1
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