248 research outputs found
Nonlocal reflection by photonic barriers
The time behaviour of microwaves undergoing partial reflection by photonic
barriers was measured in the time and in the frequency domain. It was observed
that unlike the duration of partial reflection by dielectric layers, 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. Evanescent modes correspond to
photonic tunnelling in quantum mechanics.Comment: 8 pages, 5 figure
Tunneling Violates Special Relativity
Experiments with evanescent modes and tunneling particles have shown that i)
their signal velocity may be faster than light, ii) they are described by
virtual particles, iii) they are nonlocal and act at a distance, iv)
experimental tunneling data of phonons, photons, and electrons display a
universal scattering time at the tunneling barrier front, and v) the properties
of evanescent, i.e. tunneling modes is not compatible with the special theory
of relativity
Lorentz Invariant Superluminal Tunneling
It is shown that superluminal optical signalling is possible without
violating Lorentz invariance and causality via tunneling through photonic band
gaps in inhomogeneous dielectrics of a special kind.Comment: 10 pages revtex, no figure, more discussions added, submitted to
Phys. Rev.
Theoretical evidence for the superluminality of evanescent modes
Though both theoretical and experimental investigations have revealed the
superluminal behavior of evanescent electromagnetic waves, there are many
disputes about the physical meaning and validity of such superluminal
phenomenon, which is due to the fact that the traditional investigations are
based on the theory of tunneling time, and concerned with the problem of what
the group velocity of evanescent waves means. In this paper, by studying the
quantum probability amplitude for photons to propagate over a spacelike
interval along an undersized waveguide, we present theoretical evidence for
such superluminality
Measurement of Superluminal optical tunneling times in double-barrier photonic bandgaps
Tunneling of optical pulses at 1.5 micron wavelength through double-barrier
periodic fiber Bragg gratings is experimentally investigated. Tunneling time
measurements as a function of barrier distance show that, far from the
resonances of the structure, the transit time is paradoxically short, implying
Superluminal propagation, and almost independent of the distance between the
barriers. These results are in agreement with theoretical predictions based on
phase time analysis and also provide an experimental evidence, in the optical
context, of the analogous phenomenon expected in Quantum Mechanics for
non-resonant superluminal tunneling of particles across two successive
potential barriers. [Attention is called, in particular, to our last Figure].
PACS nos.: 42.50.Wm, 03.65.Xp, 42.70.Qs, 03.50.De, 03.65.-w, 73.40.GkComment: LaTeX file (8 pages), plus 5 figure
Recovering the stationary phase condition for accurately obtaining scattering and tunneling times
The stationary phase method is often employed for computing tunneling {\em
phase} times of analytically-continuous {\em gaussian} or infinite-bandwidth
step pulses which collide with a potential barrier. The indiscriminate
utilization of this method without considering the barrier boundary effects
leads to some misconceptions in the interpretation of the phase times. After
reexamining the above barrier diffusion problem where we notice the wave packet
collision necessarily leads to the possibility of multiple reflected and
transmitted wave packets, we study the phase times for tunneling/reflecting
particles in a framework where an idea of multiple wave packet decomposition is
recovered. To partially overcome the analytical incongruities which rise up
when tunneling phase time expressions are obtained, we present a theoretical
exercise involving a symmetrical collision between two identical wave packets
and a one dimensional squared potential barrier where the scattered wave
packets can be recomposed by summing the amplitudes of simultaneously reflected
and transmitted waves.Comment: 32 pages, 5 figures, 1 tabl
Limitations on the principle of stationary phase when it is applied to tunneling analysis
Using a recently developed procedure - multiple wave packet decomposition -
here we study the phase time formulation for tunneling/reflecting particles
colliding with a potential barrier. To partially overcome the analytical
difficulties which frequently arise when the stationary phase method is
employed for deriving phase (tunneling) time expressions, we present a
theoretical exercise involving a symmetrical collision between two identical
wave packets and an one-dimensional rectangular potential barrier. Summing the
amplitudes of the reflected and transmitted waves - using a method we call
multiple peak decomposition - is shown to allow reconstruction of the scattered
wave packets in a way which allows the stationary phase principle to be
recovered.Comment: 17 pages, 2 figure
Characterization of high-temperature PbTe p-n junctions prepared by thermal diffusion and by ion-implantation
We describe here the characteristics of two types of high-quality PbTe
p-n-junctions, prepared in this work: (1) by thermal diffusion of In4Te3 gas
(TDJ), and (2) by ion implantation (implanted junction, IJ) of In (In-IJ) and
Zn (Zn-IJ). The results, as presented here, demonstrate the high quality of
these PbTe diodes. Capacitance-voltage and current-voltage characteristics have
been measured. The measurements were carried out over a temperature range from
~ 10 K to ~ 180 K. The latter was the highest temperature, where the diode
still demonstrated rectifying properties. This maximum operating temperature is
higher than any of the earlier reported results.
The saturation current density, J0, in both diode types, was ~ 10^-5 A/cm2 at
80 K, while at 180 K J0 ~ 10^-1 A/cm2 in TDJ and ~ 1 A/cm2 in both
ion-implanted junctions. At 80 K the reverse current started to increase
markedly at a bias of ~ 400 mV for TDJ, and at ~550 mV for IJ. The ideality
factor n was about 1.5-2 for both diode types at 80 K. The analysis of the C-V
plots shows that the junctions in both diode types are linearly graded. The
analysis of the C-V plots allows also determining the height of the junction
barrier, the concentrations and the concentration gradient of the impurities,
and the temperature dependence of the static dielectric constant. The
zero-bias-resistance x area products (R0Ae) at 80 K are: 850 OHMcm2 for TDJ,
250 OHMcm2 for In-IJ, and ~ 80 OHMcm2 for Zn-IJ, while at 180 K R0Ae ~ 0.38
OHMcm2 for TDJ, and ~ 0.1 OHMcm2 for IJ. The estimated detectivity is: D* ~
10^10 cmHz^(1/2)/W up to T=140 K, determined mainly by background radiation,
while at T=180 K, D* decreases to 108-107 cmHz^(1/2)/W, and is determined by
the Johnson noise
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. Due to the
analogy of the Schr\"odinger and the Helmholtz equation this phenomenon is
expected to be observable for electromagnetic wave propagation. Experimental
data of electromagnetic wells realized by wave guides filled with different
dielectrics confirm this conjecture now.Comment: 10 pages, 6 figure
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