510 research outputs found
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
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.Comment: 10 pages, 6 figure
Superluminal behavior and the Minkowski space-time
Bessel X-waves, or Bessel beams, have been extensively studied in last years,
especially with regard to the topic of superluminality in the propagation of a
signal. However, in spite of many efforts devoted to this subject, no definite
answer has been found, mainly for lack of an exact definition of signal
velocity. The purpose of the present work is to investigate the field of
existence of Bessel beams in order to overcome the specific question related to
the definition of signal velocity. Quite surprisingly, this field of existence
can be represented in the Minkowski space-time by a Super-Light Cone which
wraps itself around the well-known Light Cone. So, the change in the upper
limit of the light velocity does not modify the fundamental low of the
relativity and the causal principle.Comment: 3 pages, 2 figure
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.Comment: 6 pages, 4 figure
- …