Search results for "light"

Effects of the Lorentz invariance violation in Coulomb interaction in nuclei and atoms

2016

Anisotropy in the speed of light that has been constrained by Michelson-Morley-type experiments also generates anisotropy in the Coulomb interactions. This anisotropy can manifest itself as an energy anisotropy in nuclear and atomic experiments. Here the experimental limits on Lorentz violation in 21Ne are used to improve the limits on the Lorentz symmetry in the photon sector, namely the anisotropy of the speed of light and the Coulomb interactions, by 7 orders of magnitude in comparison with previous experiments: the speed of light is isotropic to a part in E-28.

2017

In the EXILL campaign a highly efficient array of high purity germanium (HPGe) detectors was operated at the cold neutron beam facility PF1B of the Institut Laue-Langevin (ILL) to carry out nuclear structure studies, via measurements of γ-rays following neutron-induced capture and fission reactions. The setup consisted of a collimation system producing a pencil beam with a thermal capture equivalent flux of about 108 n s−1cm−2 at the target position and negligible neutron halo. The target was surrounded by an array of eight to ten anti-Compton shielded EXOGAM Clover detectors, four to six anti-Compton shielded large coaxial GASP detectors and two standard Clover detectors. For a part of the…

New results from testing of coplanar-grid CdZnTe detectors

2005

New results from studies of coplanar-grid CdZnTe (CZT) detectors are presented. The coplanar-grid detectors were investigated by using a highly collimated X-ray beam available at Brookhaven's National Synchrotron Light Source and by applying a pulse-shape analysis. The coplanar-grid detector operates as a single-carrier device. Despite the fact that its operational principle is well known and has been investigated by many groups in the past, we found some new details that may explain the performance limits of these types of devices. The experimental results have been confirmed by extensive computer modeling.

Improving the performance of CdZnTe detectors using infrared stimulation

2011

The influence of monochromatic optical stimulation with wavelengths from 400 nm to 1100 on characteristics of the CdZnTe quasi-hemispherical detectors was studied. It was found that illumination with infrared (IR) light of wavelengths (870–900 nm) close to the absorption edge of the CdZnTe significantly improves the detectors performance at room temperature. Improvement can be achieved with low-intensity IR illumination of about 1–10 µW. The higher intensity illumination leads to degradation of the detector spectrometric characteristics. Infrared radiation penetrates into the detector sensitive volume, change the balance equilibrium between free and trapped carriers, leading to improve char…

TIME-RESOLVED EMISSION FROM BRIGHT HOT PIXELS OF AN ACTIVE REGION OBSERVED IN THE EUV BAND WITH SDO/AIA AND MULTI-STRANDED LOOP MODELING

2015

Evidence for small amounts of very hot plasma has been found in active regions and might be the indication of an impulsive heating, released at spatial scales smaller than the cross section of a single loop. We investigate the heating and substructure of coronal loops in the core of one such active region by analyzing the light curves in the smallest resolution elements of solar observations in two EUV channels (94 A and 335 A) from the Atmospheric Imaging Assembly on-board the Solar Dynamics Observatory. We model the evolution of a bundle of strands heated by a storm of nanoflares by means of a hydrodynamic 0D loop model (EBTEL). The light curves obtained from the random combination of tho…

Dark-soliton-like pulse-train generation from induced modulational polarization instability in a birefringent fiber

1998

Theory and experiments show that the nonlinear development of the modulational polarization instability of an intense light beam in a normally dispersive, low-birefringence optical fiber leads to ultrashort dark-soliton-like trains with repetition rates in the terahertz range in the polarization orthogonal to the pump.

Reduction of focus size in tightly focused linearly polarized beams

2004

The electromagnetic theory predicts that when a linearly polarized collimated field is focused by a high-angle focusing system, components perpendicular to the initial polarization are generated. The use of annular masks to reduce the area of the focal spot usually increases the magnitude of this phenomenon, known as depolarization. We present a class of masks, the three-ring masks, which are important because they narrow the central lobe of the focal intensity distribution without increasing the depolarization. This can be very useful in modern optical applications, such as confocal microscopy or multiphoton scanning microscopy.

Harmonic Coupling of the Red Noise in X‐Ray Pulsars

1997

The power spectra of X-ray pulsars often show the presence of a red-noise component. This noise is produced by aperiodic variability believed to be associated with instabilities that seem to occur in accretion flows onto compact objects. In this paper we discuss how, independently of the details of the physical processes that generate these instabilities, a careful analysis of the power spectra can furnish some constraints on the distance from the stellar surface at which the sudden energy release associated with the instabilities occurs. In particular, any aperiodic variability coming from the accretion flow funneled toward the magnetic poles should be modulated at the pulsar spin period (…

Interaction-free evolution in the presence of time-dependent Hamiltonians

2015

The generalization of the concept of interaction-free evolutions (IFE) [A. Napoli, {\it et al.}, Phys. Rev. A {\bf 89}, 062104 (2014)] to the case of time-dependent Hamiltonians is discussed. It turns out that the time-dependent case allows for much more rich structures of interaction-free states and interaction-free subspaces. The general condition for the occurrence of IFE is found and exploited to analyze specific situations. Several examples are presented, each one associated to a class of Hamiltonians with specific features.

Generating highly squeezed Hybrid Laguerre-Gauss modes in large-Fresnel-number Degenerate Optical Parametric Oscillators

2008

We theoretically describe the quantum properties of a large Fresnel number degenerate optical parametric oscillator with spherical mirrors that is pumped by a Gaussian beam. The resonator is tuned so that the resonance frequency of a given transverse mode family coincides with the down-converted frequency. After demonstrating that only the lower orbital angular momentum (OAM) Laguerre-Gauss modes are amplified above threshold, we focus on the quantum properties of the rest of (classically empty) modes. We find that combinations of opposite OAM (Hybrid Laguerre-Gauss modes) can exhibit arbitrary large quadrature squeezing for the lower OAM non amplified modes.