A. Ranfagni

Observation of Zenneck-type waves in microwave propagation experiments

The debated question of the superluminal speed of information remains open to different interpretations in spite of recent, apparently conclusive, contributions. A different point of view is here considered, which is based on experimental results of microwave propagation experiments, in far-field conditions. They support the hypothesis of the existence of fast waves of the Zenneck type.

Pupils with super-resolution

Abstract In 1952 Toraldo di Francia [Il Nuovo Cimento (Suppl.) 9 (1952) 426] proposed an intriguing concept to increase the optical resolving power. As a consequence, this theory could seem in contradiction with Heisenbergs uncertainty principle. In this Letter we report on the results of a microwave investigation which demonstrate the rightness of such theoretical predictions. Their interpretation, in relation to the uncertainty principle, is then discussed.

Beyond the diffraction limit: Super-resolving pupils

In an attempt to transfer the results obtained with super-gain antennas to optical systems in order to increase the resolving power, an original way for overcoming the diffraction limit was proposed in 1952. In this work, we report on the results of microwave experiments which demonstrate the correctness of these predictions. Their interpretation in relation to the uncertainty principle is then discussed, and a possible connection with the “weak measurement” theory is then suggested.

SUPERLUMINAL PROCESSES AND SIGNAL VELOCITY IN TUNNELING SIMULATION

Abstract It has been demonstrated that microwave simulation is a powerful method for studying tunneling processes and in particular tunneling time. A semiclassical interpretation, based on the telegraphers equation, turned out to be in quite good agreement with the predictions of quantum-mechanical models but it works well also in connection with superluminal behaviours recently evidenced. The aim of this work is to demonstrate how evanescent waves account for superluminal processes: the plausibility of the results is discussed on the basis of signal analysis along the lines of the Sommerfeld-Brillouin criterion, as well as in the framework of special relativity.

Semiclassical tunneling time in presence of dissipation: an optical model

The tunneling-time behaviour for a rectangular barrier, as described by a semiclassical analysis which at the top of the barrier predicts an unphysical divergence, can be sensibly improved taking into account energy losses by a simple phenomenological model. The results are comparable with the experimental data obtained by a microwave simulation.

How to employ microwaves for simulating quantum tunnelling

Abstract Delay-time results relative to a step-like microwave signal propagating in a waveguide in the cutoff region are interpreted by means of a path-integral solution of the telegrapher equation. This allows one to perform a simulation of the quantum tunnelling based on the analogy between (relativistic) particle motion and electromagnetic wave propagation with inclusion of dissipative effects.

Optical gain measurements in doped alkali-halides

Abstract In order to verify the possibility of obtaining laser action in doped alkali-halides crystals, optical amplification measurements have been performed by the amplified spontaneous emission (ASE) technique. Results obtained in CsI : In(Tl) crystal are reported and discussed.

Traversal Time as Deduced from Decay Time Measurements in Josephson Junctions

The macroscopic quantum tunneling rate out of the metastable state of a Josephson junction has been measured in a range of temperature where the quantum contribution is comparable with the thermal escape. From such measurements the traversal time of the barrier has been deduced and compared with the theoretical predictions of a semiclassical model.

The role of the forerunner in the tunneling time determination

Abstract The problem of the tunneling time is reconsidered in relation to a microwave simulation experiment, elsewhere described. The results can be interpreted on the basis of an improved procedure already proposed by Stevens and based on the Sommerfeld-Brillouin method for determining the signal velocity in a dispersive medium. We find that for tunneling processes a decisive role is played by the signal-forerunner and the resulting times are in qualitative agreement with the predictions of other quantum mechanical models.

Optical gain measurements with the amplified spontaneous emission technique

An amplified spontaneous emission technique is described for the evaluation of optical gain as a function of the length of the pumped pencil-shaped area of the active medium. Continuous measurements of emission intensity are made while a movable screen varies the pumped length. Inhomogeneities of the pumping beam can be taken into account by employing two different pump intensities in alternate sequence. The system allows low-gain measurements minimizing the effect of pump intensity drifts, rf interferences, and efficiency loss of the active medium. In the presence of reabsorption the system suffers some modifications.