571 research outputs found
Quantum-Fluctuation-Initiated Coherence in Multi-Octave Raman Optical Frequency Combs
We show experimentally and theoretically that the spectral components of a
multi-octave frequency comb spontaneously created by stimulated Raman
scattering in a hydrogen-filled hollow-core photonic crystal fiber exhibit
strong self coherence and mutual coherence within each 12 ns driving laser
pulse. This coherence arises in spite of the field's initiation being from
quantum zero-point fluctuations, which causes each spectral component to show
large phase and energy fluctuations. This points to the possibility of an
optical frequency comb with nonclassical correlations between all comb lines.Comment: Accepted for publication, Physical Review Letters, 201
NATURAL POLYMERS: CELLULOSE, CHITIN, CHITOSAN, GELATIN, STARCH, CARRAGEENAN, XYLAN AND DEXTRAN
Biopolymers have been investigated for drug fields. They are widely being studied because of their non-toxic and biocompatible in nature. Biopolymers are used in industries as diverse as paper, plastics, food, textiles, pharmaceuticals, and cosmetics.This review covers different natural polymers, recent techniques applied in their processing and characterization. Advanced applications of natural polymers, including chitin, chitosan, alginate, etc., are discussed
Gap solitons in spatiotemporal photonic crystals
We generalize the concept of nonlinear periodic structures to systems that
show arbitrary spacetime variations of the refractive index. Nonlinear pulse
propagation through these spatiotemporal photonic crystals can be described,
for shallow nonstationary gratings, by coupled mode equations which are a
generalization of the traditional equations used for stationary photonic
crystals. Novel gap soliton solutions are found by solving a modified massive
Thirring model. They represent the missing link between the gap solitons in
static photonic crystals and resonance solitons found in dynamic gratings.Comment: 3 figures, submitte
Deeply-trapped molecules in self-nanostructured gas-phase material
Since the advent of atom laser-cooling, trapping or cooling natural molecules
has been a long standing and challenging goal. Here, we demonstrate a method
for laser-trapping molecules that is radically novel in its configuration, in
its underlined physical dynamics and in its outcomes. It is based on
self-optically spatially-nanostructured high pressure molecular hydrogen
confined in hollow-core photonic-crystal-fibre. An accelerating
molecular-lattice is formed by a periodic potential associated with Raman
saturation except for a 1-dimentional array of nanometer wide and
strongly-localizing sections. In these sections, molecules with a speed of as
large as 1800 m/s are trapped, and stimulated Raman scattering in the
Lamb-Dicke regime occurs to generate high power forward and backward-Stokes
continuous-wave laser with sideband-resolved sub-Doppler emission spectrum. The
spectrum exhibits a central line with a sub-recoil linewidth of as low as 14
kHz, more than 5 orders-of-magnitude narrower than in conventional Raman
scattering, and sidebands comprising Mollow triplet, molecular
motional-sidebands and four-wave-mixing.Comment: 28 pages 1-12 for main manuscript 13-28 for Methodes and appendices 4
figures for Main manuscript 12 figures for the Methods par
Light and gas confinement in hollow-core photonic crystal fibre based photonic microcells
We review the recent progress on the understanding of optical guidance mechanisms in hollow-core photonic crystal fibres, and on the quantum and nonlinear optical applications of photonic microcells based on this fibre form. Two classes of hollow-core photonic crystal fibre are identified: one guides via a photonic bandgap and the other guides by virtue of an inhibited coupling between core and cladding mode constituents. For the former fibre type, we explore how the bandgap is formed using a photonic analogue of the tight-binding model and how it is related to the anti-resonant reflection optical waveguide guidance. For the second type of fibre, which can guide over a broad wavelength range, we examine the nature of the inhibited coupling. We describe a technique for the fabrication of photonic microcells that can accommodate vacuum pressures, and we finish by showing the latest results on electromagnetically induced transparency in a rubidium filled hollow-core photonic crystal fibre, the CW-pumped hydrogen Raman laser and the generation of multi-octave spanning stimulated Raman scattering spectral combs
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Raman gas self-organizing into deep nano-trap lattice
Trapping or cooling molecules has rallied a long-standing effort for its impact in exploring new frontiers in physics and in finding new phase of matter for quantum technologies. Here we demonstrate a system for light-trapping molecules and stimulated Raman scattering based on optically self-nanostructured molecular hydrogen in hollow-core photonic crystal fibre. A lattice is formed by a periodic and ultra-deep potential caused by a spatially modulated Raman saturation, where Raman-active molecules are strongly localized in a one-dimensional array of nanometre-wide sections. Only these trapped molecules participate in stimulated Raman scattering, generating high-power forward and backward Stokes continuous-wave laser radiation in the Lamb-Dicke regime with sub-Doppler emission spectrum. The spectrum exhibits a central line with a sub-recoil linewidth as low as ∼14 kHz, more than five orders of magnitude narrower than conventional-Raman pressure-broadened linewidth, and sidebands comprising Mollow triplet, motional sidebands and four-wave mixing
Superradiance from lattice-confined atoms inside hollow core fibre
Unravelling superradiance, also known as superfluorescence, relies on an ensemble of phase-matched dipole oscillators and the suppression of inhomogeneous broadening. Here we report a superradiance platform that combines an optical lattice free from the ac Stark shift and a hollow-core photonic crystal fibre, enabling an extended atom-light interaction over 2 mm free from the Doppler effect. This system allows control of the atom spatial distribution and spectral homogeneity whilst efficiently coupling the radiation field to an optical fibre. The experimentally-observed and theoretically-corroborated temporal, spectral and spatial dynamic behaviours of the superradiance, e.g., superradiance ringing and density-dependent frequency shift, demonstrate a unique interplay between the trapped atoms and the fibre-guided field with multiple transverse modes. Our theory indicates that the resulting temporal evolution of the guided light shows a minimal beam radius of 3.1 mu m which is three times smaller than that of the lowest-loss fibre mode
Effect of the mechanical treatment of alumina on thermal, morphological and dielectric properties of LDPE/Al2O3 composites
Composites of LDPE filled with different amounts of alumina Al2O3 were prepared using co-mixing technique and melt-mixing. This technique, which is easy, non-toxic and inexpensive, has been successfully used in our laboratory for different polyolefins/metal oxides nanocomposites elaboration. Samples containing 0.5, 1 and 2 wt% of alumina, were prepared by melt-mixing at 190 °C without any chemical treatment or coupling agent. The effect of alumina treatment was studied. The Al2O3 was first co-mixed with the stearic acid then added to the polymer. The stearic acid melts at 70 °C, thus ensuring the dispersion of the covered filler particles into the polymeric matrix, which leads to better experimental results. The morphological characterization was carried out by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The thermal properties were investigated by thermogravimetric analysis (TGA). The electrical conductivity was also studied. The microstructure-properties relationships were also investigated. The composites prepared with the co-mixed Al2O3 were compared to those prepared with the neat Al2O3. The thermogravimetric (TGA) results showed an enhancement of 55 °C in the thermal stability for the LDPE/Al2O3 composition containing 1 wt% of treated Al2O3. The electrical conductivity results showed also an optimum value of 6.6.10–7 Ù–1 cm–1 for the same composition.Keywords: Composites, LDPE, Al2O3 nanoparticles, stearic acid, co-mixing metho
Contribution à l'étude du régime alimentairedu barbeau (Barbus barbus callensis Valenciennes, 1842) d'un cours d'eau du Moyen-Atlas (Maroc) : Oued Boufekrane
L'étude du régime alimentaire du barbeau (Barbus barbus callensis Valenciennes, 1842) de l'Oued Boufekrane a été réalisée sur 1 021 poissons, capturés entre janvier 1998 et juin 1999. Cette espèce présente un rythme saisonnier d'activité alimentaire. Ainsi, avec des faibles taux de vacuité, l'été et le printemps sont les saisons de forte activité alimentaire. Cette dernière diminue durant l'automne et l'hiver. Le caractère omnivore du barbeau est vérifié ; son régime alimentaire se compose essentiellement de larves d'Insectes et de débris de végétaux. Les jeunes individus (moins de 13 cm de longueur) ont une tendance zoophage, dominée par les larves de Diptères et d'Éphéméroptères. En revanche, les plus âgés présentent une tendance phytophage qui reflète l'opportunisme de ce poisson et explique ainsi, son adaptation aux conditions trophiques du milieu, caractérisées par une pauvreté en benthos.The diet of the barbel (Barbus barbus callensis Vallenciennes, 1842) in Boufekrane stream was studied on 1021 fish catched between January 1998 and June 1999.This species presented a seasonal rhythm. So, with the low rate of vacuity index, the summer and the spring were the seasons of intense alimentary activity. This activity regressed during automn and winter. The omnivorous character of the barbel was verified. The diet was composed essentially from insect larvae and plant's sherd. The young barbel (length is less than 13 cm) have zoophagous tendency. Their diet was dominated by Diptera and Ephemeroptera larvae. But, the old ones present a phytophagous tendency the opportunism of this species and the plasicity of its diet. This behavior explain the adaptability of this species to trophic conditions in the stream which contained low density of benthic fauna
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