A. Haibel

Pulse reflection by photonic barriers.

The time behavior of microwaves undergoing partial reflection by photonic barriers was measured in the time and in the frequency domain. It was observed that for opaque barriers the reflection delay is almost independent of the barriers length. This result corresponds to the Hartman effect in transmission.

Basics of superluminal signals

The paper elucidates the physical basis of experimental results on superluminal signal velocity. It will be made plausible that superluminal signals do not violate the principle of causality but they can shorten the vacuum time span between cause and effect. The causal behaviour is based on the property that a physical signal has a finite duration as a result of its frequency band limitation.

Universal Relationship of Time and Frequency in Photonic Tunnelling

Tunnelling transit time for a frustrated total internal reflection in a double-prism experiment was measured using microwave radiation. We have found that the transit time is of the same order of magnitude as the corresponding transit time measured either in an undersized waveguide (evanescent modes) or in a photonic lattice. Moreover we have established that in all such experiments the tunnelling transit time is approximately equal to the reciprocal 1/f of the corresponding frequency of radiation.

Negative phase time for scattering at quantum wells: a microwave analogy experiment.

If a quantum mechanical particle is scattered by a potential well, the wave function of the particle can propagate with negative phase time. Because of the analogy of the Schrödinger and Helmholtz equations this phenomenon is expected to be observable for electromagnetic wave propagation. Experimental data for electromagnetic wells realized by waveguides filled with different dielectrics now confirm this conjecture.

From superluminal velocity to time machines

Various experiments have shown superluminal group and signal velocities. Experiments were essentially carried out with microwave tunneling [1], with infrared waves by frustrated total internal reflection [2] and in a linear resonant molecular absorber with millimeter waves [3]. According to text books a superluminal signal velocity violates Einstein causality implying that cause and effect can be changed and time machines known from science fiction could be constructed. This naive analysis, however, assumes a signal to be a point in the time dimension neglecting its finite duration. A signal is not presented by a point nor by its front, but by its total length. On the other hand a signal energy is finite thus its frequency band is limited, the latter is a fundamental physical property in consequence of field quantization with quantum hν. All superluminal experiments have been carried out with rather narrow frequency bands. The narrow band width is a condition sine qua non to avoid pulse reshaping of the s...

NONLOCAL REFLECTION BY PHOTONIC BARRIERS

The time behaviour of partial reflection by opaque photonic barriers was measured with microwaves. It was observed that unlike the duration of partial reflection by dielectric sheets, the measured reflection duration of barriers is independent of their length. The experimental results point to a nonlocal behaviour of evanescent modes at least over a distance of some ten wavelengths.

On Superluminal Photonic Tunnelling

Evanescent modes or the tunnelling process are characterized by an imaginary wave number. These special solutions of the Helmholtz and of the Schrodinger equations first noticed in connection with the total reflection were said to have no physical meaning about 200 years ago. Last century the tunnelling problem in quantum mechanics has been described by the phase time approach. The phase time approach yields the group velocity of a wave packet (see e.g. Hartman, 1962). Nowadays the phase time approach is used in network analyzers to determine the group velocity of an electromagnetic wave in devices.