144 research outputs found
Superfluid Motion of Light
Superfluidity, the ability of a fluid to move without dissipation, is one of
the most spectacular manifestations of the quantum nature of matter. We explore
here the possibility of superfluid motion of light. Controlling the speed of a
light packet with respect to a defect, we demonstrate the presence of
superfluidity and, above a critical velocity, its breakdown through the onset
of a dissipative phase. We describe a possible experimental realization based
on the transverse motion through an array of waveguides. These results open new
perspectives in transport optimization.Comment: 4 pages, 3 figure
Propagation of relativistic charged particles in ultracold atomic gases with Bose-Einstein condensates
We study theoretically some effects produced by a propagation of the charged
particles in dilute gases of alkali-metal atoms in the state with Bose-Einstein
condensates. The energy change of the high-speed (relativistic) particle that
corresponds to the Cherenkov effect in the condensate is investigated. We show
that in the studied cases the particle can both loose and receive the energy
from a gas. We find the necessary conditions for the particle acceleration in
the multi-component condensate. It is shown that the Cherenkov effect in
Bose-Einstein condensates can be used also for defining the spectral
characteristics of atoms.Comment: 6 pages, 3 figure
Spatial distribution of Cherenkov radiation in periodic dielectric media
The nontrivial dispersion relation of a periodic medium affects both the
spectral and the spatial distribution of Cherenkov radiation. We present a
theory of the spatial distribution of Cherenkov radiation in the far-field zone
inside arbitrary three- and two-dimensional dielectric media. Simple analytical
expressions for the far-field are obtained in terms of the Bloch mode
expansion. Numerical examples of the Cherenkov radiation in a two-dimensional
photonic crystal is presented. The developed analytical theory demonstrates
good agreement with numerically rigorous finite-difference time-domain
calculations.Comment: 14 pages, 5 figures, Journal of Optics A (in press
Prototype 9.7 m Schwarzschild-Couder telescope for the Cherenkov Telescope Array: status of the optical system
The Cherenkov Telescope Array (CTA) is an international project for a
next-generation ground-based gamma ray observatory, aiming to improve on the
sensitivity of current-generation experiments by an order of magnitude and
provide energy coverage from 30 GeV to more than 300 TeV. The 9.7m
Schwarzschild-Couder (SC) candidate medium-size telescope for CTA exploits a
novel aplanatic two-mirror optical design that provides a large field of view
of 8 degrees and substantially improves the off-axis performance giving better
angular resolution across all of the field of view with respect to
single-mirror telescopes. The realization of the SC optical design implies the
challenging production of large aspherical mirrors accompanied by a
submillimeter-precision custom alignment system. In this contribution we report
on the status of the implementation of the optical system on a prototype 9.7 m
SC telescope located at the Fred Lawrence Whipple Observatory in southern
Arizona.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Busan, Korea. All CTA contributions at arXiv:1709.0348
Mapping local optical densities of states in silicon photonic structures with nanoscale electron spectroscopy
Relativistic electrons in a structured medium generate radiative losses such
as Cherenkov and transition radiation that act as a virtual light source,
coupling to the photonic densities of states. The effect is most pronounced
when the imaginary part of the dielectric function is zero, a regime where in a
non-retarded treatment no loss or coupling can occur. Maps of the resultant
energy losses as a sub-5nm electron probe scans across finite waveguide
structures reveal spatial distributions of optical modes in a spectral domain
ranging from near-infrared to far ultraviolet.Comment: 18 pages, 4 figure
ASTRI SST-2M prototype and mini-array simulation chain, data reduction software, and archive in the framework of the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) is a worldwide project aimed at building
the next-generation ground-based gamma-ray observatory. Within the CTA project,
the Italian National Institute for Astrophysics (INAF) is developing an
end-to-end prototype of the CTA Small-Size Telescopes with a dual-mirror
(SST-2M) Schwarzschild-Couder configuration. The prototype, named ASTRI SST-2M,
is located at the INAF "M.C. Fracastoro" observing station in Serra La Nave
(Mt. Etna, Sicily) and is currently in the scientific and performance
validation phase. A mini-array of (at least) nine ASTRI telescopes has been
then proposed to be deployed at the Southern CTA site, by means of a
collaborative effort carried out by institutes from Italy, Brazil, and
South-Africa. The CTA/ASTRI team is developing an end-to-end software package
for the reduction of the raw data acquired with both ASTRI SST-2M prototype and
mini-array, with the aim of actively contributing to the global ongoing
activities for the official data handling system of the CTA observatory. The
group is also undertaking a massive Monte Carlo simulation data production
using the detector Monte Carlo software adopted by the CTA consortium.
Simulated data are being used to validate the simulation chain and evaluate the
ASTRI SST-2M prototype and mini-array performance. Both activities are also
carried out in the framework of the European H2020-ASTERICS (Astronomy ESFRI
and Research Infrastructure Cluster) project. A data archiving system, for both
ASTRI SST-2M prototype and mini-array, has been also developed by the CTA/ASTRI
team, as a testbed for the scientific archive of CTA. In this contribution, we
present the main components of the ASTRI data handling systems and report the
status of their development.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Bexco, Busan, Korea. All CTA contributions at arXiv:1709.0348
Cherenkov Radiation from Pairs and Its Effect on Induced Showers
We calculate the Cherenkov radiation from an pair at small
separations, as occurs shortly after a pair conversion. The radiation is
reduced (compared to that from two independent particles) when the pair
separation is smaller than the wavelength of the emitted light. We estimate the
reduction in light in large electromagnetic showers, and discuss the
implications for detectors that observe Cherenkov radiation from showers in the
Earth's atmosphere, as well as in oceans and Antarctic ice.Comment: Final version, with minor changes, to appear in PRD. 5 pages with 4
figure
Onset of Wave Drag due to Generation of Capillary-Gravity Waves by a Moving Object as a Critical Phenomenon
The onset of the {\em wave resistance}, via generation of capillary gravity
waves, of a small object moving with velocity , is investigated
experimentally. Due to the existence of a minimum phase velocity for
surface waves, the problem is similar to the generation of rotons in superfluid
helium near their minimum. In both cases waves or rotons are produced at
due to {\em Cherenkov radiation}. We find that the transition to the
wave drag state is continuous: in the vicinity of the bifurcation the wave
resistance force is proportional to for various fluids.Comment: 4 pages, 7 figure
Finite temperature Cherenkov radiation in the presence of a magnetodielectric medium
A canonical approach to Cherenkov radiation in the presence of a
magnetodielectric medium is presented in classical, nonrelativistic and
relativistic quantum regimes. The equations of motion for the canonical
variables are solved explicitly for both positive and negative times. Maxwell
and related constitute equations are obtained. In the large-time limit, the
vector potential operator is found and expressed in terms of the medium
operators. The energy loss of a charged particle, emitted in the form of
radiation, in finite temperature is calculated. A Dirac equation concerning the
relativistic motion of the particle in presence of the magnetodielectric medium
is derived and the relativistic Cherenkov radiation at zero and finite
temperature is investigated. Finally, it is shown that the Cherenkov radiation
in nonrelativistic and relativistic quantum regimes, unlike its classical
counterpart, introduces automatically a cutoff for higher frequencies beyond
which the power of radiation emission is zero.Comment: To be appear in PR
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