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D. Mugnai

Publications and source records attributed to D. Mugnai.

10 recordsLinked to original sources
arXiv2014

The $A_T$ emission of KCl:Tl interpreted as a double $A_T+A_X$ emission

The experimental evidence of an anomalous behavior in the decay times of Tl$^+$-like impurity centers in alkali-halide crystals has generated a revival of interest with respect to these materials. We discuss here about the possibility that the $A_T$ emission of KCl:Tl can be considered as a double emission, namely as a superposition of the $A_T$ and $A_X$ emission bands. The plausibility of this hypothesis is discussed in the light of the available, old and recent, experimental features. A quantitative test of this assumption is performed in the framework of a model which demonstrates to be suitable for interpreting other similar cases.

cond-mat.mtrl-sci↗
arXiv2010

Propagation of Bessel beams from a dielectric to a conducting medium

Recently, the use of Bessel beams in evaluating the possibility of using them for a new generation of GPR (ground penetrating radar) systems has been considered. Therefore, an analysis of the propagation of Bessel beam in conducting media is worthwhile. We present here an analysis of this type. Specifically, for normal incidence we analyze the propagation of a Bessel beam coming from a perfect dielectric and impinging on a conducting medium, i.e. the propagation of a Bessel beam generated by refracted inhomogeneous waves. The remarkable and unexpected result is that the incident Bessel beam does not change its shape even when propagating in the conducting medium.

physics.optics↗
arXiv2010

A short note on the propagation of a Bessel beam in conducting media

Recently, the use of Bessel beams in evaluating the possibility of using them for a new generation of GPR (ground penetrating radar) systems has been considered. Therefore, an analysis of the propagation of Bessel beam in conducting media is worthwhile. We present here an analysis of this type. Specifically, for normal incidence we analyze the propagation of a Bessel beam coming from a perfect dielectric and impinging on a conducting medium, i.e. the propagation of a Bessel beam generated by refracted inhomogeneous waves. The remarkable and unexpected result is that the incident Bessel beam does not change its shape even when propagating in the conducting medium.

physics.optics↗
arXiv2006

Bessel-X waves: superluminal propagation and the Minkowski space-time

Superluminal behavior has been extensively studied in recent years, especially with regard to the topic of superluminality in the propagation of a signal. Particular interest has been devoted to Bessel-X waves propagation, since some experimental results showed that these waves have both phase and group velocities greater that light velocity c. However, because of the lack of an exact definition of signal velocity, no definite answer about the signal propagation (or velocity of information) has been found. The present paper is a short note that deals in a general way with this vexed question. By analyzing the field of existence of the Bessel X-wave in pseudo-Euclidean space-time, it is possible to give a general description of the propagation, and to overcome the specific question related to a definition of signal velocity.

physics.optics↗
arXiv2005

Bessel beam propagation: Energy localization and velocity

The propagation of a Bessel beam (or Bessel-X wave) is analyzed on the basis of a vectorial treatment. The electric and magnetic fields are obtained by considering a realistic situation able to generate that kind of scalar field. Specifically, we analyze the field due to a ring-shaped aperture over a metallic screen on which a linearly polarized plane wave impinges. On this basis, and in the far field approximation, we can obtain information about the propagation of energy flux and the velocity of the energy.

physics.optics↗
arXiv2005

Bessel beam through a dielectric slab at oblique incidence: the case of total reflection

The oblique incidence of a Bessel beam on a dielectric slab with refractive index n1 surrounded by a medium of a refractive index n>n1 may be studied simply by expanding the Bessel beam into a set of plane waves forming the same angle with the axis of the beam. In the present paper we examine a Bessel beam that impinges at oblique incidence onto a layer in such a way that each plane-wave component impinges with an angle larger than the critical angle.

physics.optics↗
arXiv2001

Tunneling time in the case of frustrated total reflection

The tunneling time is here investigated by means of an electromagnetic model, for a system where a gap, between two parallel planes, acts as a classically-forbidden region for an impinging pulse with incidence angle larger than the critical angle. In all cases of frustrated total reflection we obtain a superluminal behavior both for phase and group delays.

physics.optics↗
arXiv2001

Passage of a Bessel beam through a classically forbidden region

The motion of an electromagnetic wave, through a classically-forbidden region, has recently attracted renewed interest because of its implication with regard to the theoretical and experimental problems of superluminality. From an experimental point of view, many papers provide an evidence of superluminality in different physical systems. Theoretically, the problem of a passage through a forbidden gap has been treated by considering plane waves at oblique incidence into a plane parallel layer of a medium with a refractive index smaller than the index of the surrounding medium, and also confined (Gaussian) beams, still at oblique incidence. In the present paper the case of a Bessel beam is examined, at normal incidence into the layer (Secs. II and III), in the scalar approximation (Sec. IV) and by developing also a vectorial treatment (Sec. V). Conclusions are reported in Sic. VI.

physics.optics↗
arXiv2001

The tunnel effect in electromagnetic propagation

The tunnel effect is considered here within the framework of electromagnetic propagation. The classical problem of a plane gap of dielectric, surrounded on both sides by a medium with larger refraction index, is studied in the case in which an electromagnetic plane wave impinges into the gap with an incidence angle larger than the critical angle. In this condition (total reflection), the gap acts as a classically forbidden region and behaves like a tunnel. The field inside the forbidden gap consists of two evanescent waves, each one having its wavefronts normal to the interface. In the present paper we study the total field derived as a superposition of two such evanescent waves, its wavefronts, and the directions of propagation of both phase and energy.

physics.optics↗