27 research outputs found
Atomic gallium laser spectroscopy with violet/blue diode lasers
We describe the operation of two GaN-based diode lasers for the laser
spectroscopy of gallium at 403 nm and 417 nm. Their use in an external cavity
configuration enabled the investigation of absorption spectroscopy in a gallium
hollow cathode. We have analyzed the Doppler broadened profiles accounting for
hyperfine and isotope structure and extracting both the temperature and
densities of the neutral atomic sample produced in the glow discharge. We have
also built a setup to produce a thermal atomic beam of gallium. Using the
GaN-based diode lasers we have studied the laser induced fluorescence and
hyperfine resolved spectra of gallium.Comment: 10 pages, 7 figure
The transverse breathing mode of an elongated Bose-Einstein condensate
We study experimentally the transverse monopole mode of an elongated rubidium
condensate. Due to the scaling invariance of the non-linear Schr\"odinger
(Gross-Pitaevski) equation, the oscillation is monochromatic and sinusoidal at
short times, even under strong excitation. For ultra-low temperatures, the
quality factor can exceed 2000, where and
are the mode angular frequency and damping rate. This value is much
larger than any previously reported for other eigenmodes of a condensate. We
also present the temperature variation of and .Comment: 4 pages, 4 figures, submitted to PR
Drag of superfluid current in bilayer Bose systems
An effect of nondissipative drag of a superfluid flow in a system of two Bose
gases confined in two parallel quasi two-dimensional traps is studied. Using an
approach based on introduction of density and phase operators we compute the
drag current at zero and finite temperatures for arbitrary ratio of densities
of the particles in the adjacent layers. We demonstrate that in a system of two
ring-shape traps the "drag force" influences on the drag trap in the same way
as an external magnetic flux influences on a superconducting ring. It allows to
use the drag effect to control persistent current states in superfluids and
opens a possibility for implementing a Bose analog of the superconducting
Josephson flux qubit.Comment: 12 pages, 2 figures, new section is added, refs are adde
Intelligent non-colorimetric indicators for the perishable supply chain by non-wovens with photo-programmed thermal response
Spoiled perishable products, such as food and drugs exposed to inappropriate temperature, cause million illnesses every year. Risks range from intoxication due to pathogen-contaminated edibles, to suboptimal potency of temperature-sensitive vaccines. High-performance and low-cost indicators are needed, based on conformable materials whose properties change continuously and irreversibly depending on the experienced time-temperature profile. However, these systems can be limited by unclear reading, especially for colour-blind people, and are often difficult to be encoded with a tailored response to detect excess temperature over varying temporal profiles. Here we report on optically-programmed, non-colorimetric indicators based on nano-textured non-wovens encoded by their cross-linking degree. This combination allows a desired time-temperature response to be achieved, to address different perishable products. The devices operate by visual contrast with ambient light, which is explained by backscattering calculations for the complex fibrous material. Optical nanomaterials with photo-encoded thermal properties might establish new design rules for intelligent labels
Suppression and enhancement of impurity scattering in a Bose-Einstein condensate
Impurity atoms propagating at variable velocities through a trapped
Bose-Einstein condensate were produced using a stimulated Raman transition. The
redistribution of momentum by collisions between the impurity atoms and the
stationary condensate was observed in a time-of-flight analysis. The
collisional cross section was dramatically reduced when the velocity of the
impurities was reduced below the speed of sound of the condensate, in agreement
with the Landau criterion for superfluidity. For large numbers of impurity
atoms, we observed an enhancement of atomic collisions due to bosonic
stimulation. This enhancement is analogous to optical superradiance.Comment: 4 pages, 4 figure
Superfluid to solid crossover in a rotating Bose-Einstein condensed gas
The properties of a rotating Bose-Einstein condensate confined in a prolate
cylindrically symmetric trap are explored both analytically and numerically. As
the rotation frequency increases, an ever greater number of vortices are
energetically favored. Though the cloud anisotropy and moment of inertia
approach those of a classical fluid at high frequencies, the observed vortex
density is consistently lower than the solid-body estimate. Furthermore, the
vortices are found to arrange themselves in highly regular triangular arrays,
with little distortion even near the condensate surface. These results are
shown to be a direct consequence of the inhomogeneous confining potential.Comment: 4+e pages, 5 embedded figures, revte
Collective excitations of trapped Bose condensates in the energy and time domains
A time-dependent method for calculating the collective excitation frequencies
and densities of a trapped, inhomogeneous Bose-Einstein condensate with
circulation is presented. The results are compared with time-independent
solutions of the Bogoliubov-deGennes equations. The method is based on
time-dependent linear-response theory combined with spectral analysis of
moments of the excitation modes of interest. The technique is straightforward
to apply, is extremely efficient in our implementation with parallel FFT
methods, and produces highly accurate results. The method is suitable for
general trap geometries, condensate flows and condensates permeated with vortex
structures.Comment: 6 pages, 3 figures small typos fixe
Optical tweezers in a dusty universe: Modeling optical forces for space tweezers applications
Optical tweezers are powerful tools based on focused laser beams. They are able to trap, manipulate, and investigate a wide range of microscopic and nanoscopic particles in different media, such as liquids, air, and vacuum. Key applications of this contactless technique have been developed in many fields. Despite this progress, optical trapping applications to planetary exploration are still to be developed. Here we describe how optical tweezers can be used to trap and characterize extraterrestrial particulate matter. In particular, we exploit light scattering theory in the T-matrix formalism to calculate radiation pressure and optical trapping properties of a variety of complex particles of astrophysical interest. Our results open perspectives in the investigation of extraterrestrial particles on our planet, in controlled laboratory experiments, aiming for space tweezers applications: optical tweezers used to trap and characterize dust particles in space or on planetary bodies surface
Optical trapping and optical binding using cylindrical vector beams
We report on the use of cylindrical vector beams for optical manipulation of micron and sub-micron sized particles using the methods of a single-beam gradient force trap (optical tweezers) and an evanescent-field surface trap (optical binding). We have demonstrated a stable interferometric method for the synthesis of cylindrical vector beams (CVBs), and present measurements demonstrating polarization-controlled focal volume shaping using CVBs in an optical tweezers. Furthermore we show how appropriate combinations of CVBs corresponding to superpositions of optical fibre modes can be used for controlled trapping and trafficking of micro- and nanoparticles along a tapered optical fibre