Femtosecond pulses of light propagating along photonic-crystal fibres can generate a broad optical supercontinuum. This striking discovery has applications ranging from spectroscopy and metrology to ...telecommunication and medicine. Among the physical principles underlying supercontinuum generation are soliton emission, a variety of four-wave mixing processes, Raman-induced soliton self-frequency shift, and dispersive wave generation mediated by solitons. Although all of the above effects contribute to supercontinuum generation, none of them can explain the generation of blue and violet light from infrared femtosecond pump pulses. In this work we argue that the most profound role in the shaping of the short-wavelength edge of the continuum is played by the effect of radiation trapping in a gravity-like potential created by accelerating solitons. The underlying physics of this effect has a straightforward analogy with the inertial forces acting on an observer moving with a constant acceleration.
Microcavity polaritons are composite half-light half-matter quasiparticles, which have recently been demonstrated to exhibit rich physical properties, such as non-equilibrium condensation, parametric ...scattering and superfluidity. At the same time, polaritons have important advantages over photons for information processing, because their excitonic component leads to weaker diffraction and stronger interparticle interactions, implying, respectively, tighter localization and lower powers for nonlinear functionality. Here, we present the first experimental observations of bright polariton solitons in a strongly coupled semiconductor microcavity. The polariton solitons are shown to be micrometre-scale localized non-diffracting wave packets with a corresponding broad spectrum in momentum space. Unlike the solitons known in Bose condensed atomic gases, they are non-equilibrium and rely on a balance between losses and external pumping. Microcavity polariton solitons are excited on picosecond timescales, and thus have further benefits for information processing over light-only solitons in semiconductor cavity lasers, which have nanosecond response times.
We report on the spin properties of bright polariton solitons supported by an external pump to compensate losses. We observe robust circularly polarized solitons when a circularly polarized pump is ...applied, a result attributed to phase synchronization between nondegenerate TE and TM polarized polariton modes at high momenta. For the case of a linearly polarized pump, either σ+ or σ- circularly polarized bright solitons can be switched on in a controlled way by a σ+ or σ- writing beam, respectively. This feature arises directly from the widely differing interaction strengths between co- and cross-circularly polarized polaritons. In the case of orthogonally linearly polarized pump and writing beams, the soliton emission on average is found to be unpolarized, suggesting strong spatial evolution of the soliton polarization. The observed results are in agreement with theory, which predicts stable circularly polarized solitons and unstable linearly polarized solitons.
We studied the features of hydrolytic degradation of polylactic acid (PLLA) implants depending on their structural filling with hydroxyapatite (HA). The resistance to
in vitro
hydrolysis was tested ...for the following samples: PLLA without HA (control; group 1), PLLA/HA 25 wt% (group 2), and PLLA/HA 50 wt% (group 3). Samples were incubated at 37°C. In the hydrolysate, lactate, calcium ions, and inorganic phosphate were determined. Additionally, the time of appearance of visual deformation and sample disintegration was recorded. PLLA degradation was higher in samples saturated with HA. The highest resistance to deformation was noted for samples without HA. Samples with a PLLA/HA 50 wt% demonstrated the maximum degradation of PLLA in combination with lower resistance to deformation and the highest bioavailability of calcium and phosphate. Group 2 samples are most promising for clinical use.
We report propagating bound microcavity polariton soliton arrays consisting of multipeak structures either along (x) or perpendicular (y) to the direction of propagation. Soliton arrays of up to five ...solitons are observed, with the number of solitons controlled by the size and power of the triggering laser pulse. The breakup along the x direction occurs when the effective area of the trigger pulse exceeds the characteristic soliton size determined by polariton-polariton interactions. Narrowing of soliton emission in energy-momentum space indicates phase locking between adjacent solitons, consistent with numerical modeling which predicts stable multihump soliton solutions. In the y direction, the breakup originates from inhomogeneity across the wave front in the transverse direction which develops into a stable array only in the solitonic regime via phase-dependent interactions of propagating fronts.
Based on the literature search and patent studies, an overview of the purification methods of natural and technical waters from arsenic compounds was made. Promising methods to reduce arsenic ...concentration in geothermal heat carriers in Kamchatka deposits have been identified with a view to decrease the toxic discharging effect of exhausted solutions on the environment.
We report on a class of dark solitons and vortices existing in the exciton-polariton condensates and having discontinuity in their excitonic component. These solutions exist due to an intrinsic ...bistability of the exciton density in the given optical field and for nonzero detuning between the cavity and excitonic resonances. We specify a well defined energy boundary where they transform into previously known polaritonic dark solitons and vortices.
Complexes of lipopolysaccharide
(LPS)
from the bacterium
Escherichia coli
and chitosan
(CN)
with a molecular weight of 5 kDa were obtained and their supramolecular organization was studied. Using ...atomic force microscopy, it was shown that during the formation of complexes there is a transition from the micellar structure of the original LPS to linear network structures uniformly distributed over the surface of mica. The stability of LPS-CN complexes of various stoichiometries in biological media in the presence of serum proteins was investigated. It was shown that complexes with an LPS–CN ratio of 1 : 1 in the presence of serum proteins lost their surface charge and tended to aggregate while complexes with the maximum saturation of CN (1 : 5) did not aggregate under these conditions and maintained their surface charge. The effect of CNs of different molecular weights on the ability of LPS to interact with neutrophils of human whole blood was studied. It was observed that LPS-CN complexes were capable of binding to neutrophils and internalazing the cell, and this ability was enhanced in the presence of serum proteins. Chitosan exhibited the ability to suppress the synthesis of the proinflammatory cytokine TNF-α induced by LPS, not only as part of the complex but also when cells were pretreated with a polycation.
We apply the recently developed theory of frequency generation by mixing of solitons and dispersive waves Phys. Rev. E 72, 016619 (2005) to explain the observed formation, quasi-trapping and ...frequency shift of the spectral peaks at the blue edge of supercontinua generated in silica-core photonic crystal fibers.
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