We have investigated the polarization response of a dielectric to intense few-cycle laser pulses with a focus on interband tunnelling. Once charge carriers are created in an initially empty ...conduction band, they make a significant contribution to the polarization response. In particular, the coherent superposition of conduction- and valence-band states results in quantum beats. This quantum-beat part of the polarization response is affected by the excitation dynamics and attosecond-scale motion of charge carriers in an intense laser field. Our analysis shows that, with the onset of Bloch oscillations or tunnelling, the nonlinear polarization response becomes sensitive to the carrier-envelope phase of the laser pulse.
One of the main methods of protecting pipelines and machine parts against stress corrosion and hydrogen embrittlement is to test metals for hydrogen-induced cracking. The hydrogen-induced cracking ...test is a standard procedure for testing steels and titanium alloys and for studying hydrogen resistance. The experimentally revealed phenomenon of nonuniform hydrogen distribution after hydrogen charging of specimens is called the skin effect. Here we study the influence of the skin effect after hydrogen charging on the crack growth under mechanical stresses and the influence of a 50-μm-thick skin layer on the durability of bulk specimens. A corset-type cylindrical specimen with a circumferential notch is considered. The Oriani decohesion model is chosen as a hydrogen embrittlement model. The investigation is performed using our data on the real nonuniform hydrogen distribution and the literature data on hydrogen diffusion coefficients, diffusion activation energy, steel parameters, cohesive law parameters, as well as other parameters of the hydrogen embrittlement model proposed by Serebrinsky. Hydrogen redistribution is described by the diffusion law taking into account mechanical stresses. Modeling is carried out with the original finite volume code in the axisymmetric setting. Crack propagation parameters are determined. The fracture pattern is complex. Cracking first occurs by the hydrogen-enhanced decohesion mechanism and then by the conventional mechanism, which explains the experimentally observed brittle-ductile fracture behavior in tensile hydrogen-charged specimens.
The main goal of development of the new Dubna Gas-Filled Recoil Separator (DGFRS-2) is to sufficiently improve the efficiency of studies on heavy and superheavy nuclei at the Super Heavy Element ...Factory of the Flerov Laboratory of Nuclear Reactions (FLNR) at the Joint Institute for Nuclear Research. The use of beams with the intensity up to 6×1013 s−1 (10 pμA) delivered by the DC280 cyclotron requires an effective setup providing high suppression of background reaction products. The described gas-filled separator is optimized for synthesis and study of heavy isotopes produced in complete fusion reactions of massive nuclei. Basic characteristics of DGFRS-2, as well as the results of the first test experiments, are presented. In comparison to the DGFRS-1, the transmission efficiency was doubled, and the background was reduced by a factor 200.
This paper presents the results from the generation of elliptical high harmonics in a process of two-color elliptical laser field interaction with a single atom. Numerical simulations are performed ...for different values of ellipticities of the two-color driving laser field (the fundamental and the second harmonics of the Ti:Sapphire laser), together with their relative helicity. The dependency of the intensity and ellipticity of harmonics as functions of the ellipticity of the driving field components and their relative helicity is discussed. The presence of the sequence of two strong and one weak harmonics in the generated spectra in the case of a counter rotating bicircular laser field is demonstrated in this paper. The origin of weak harmonics generation is also discussed.
Abstract
Recently, increased attention has been paid to issues of information and analytical support for the Russian Arctic security. However, risk management problems are especially acute for lower ...levels of management hierarchy. Therefore, it is relevant to consider issues of managing technogenic-ecological industrial-natural complexes safety of the Arctic. In this article, these features are considered on the example of a heat power plant. Accidents related to oil and oil products spills are considered as a typical example. In first part of the work, main goals and objectives of prevention, forecasting and elimination of accidents consequences are given, the features of operational management in event of an emergency are revealed. It is shown that Arctic industrial-natural complexes safety management is a complex interdisciplinary area of fundamental and applied research. The structure of information-analytical complex for risk management has been formed. The second section presents some research and developments in field of information-analytical support of industrial-natural safety. Directions for further research are outlined.
Strain effect on indium incorporation and optical transitions in bulk InGaN and GaN/InGaN/GaN quantum wells (QWs) coherently grown on GaN substrates with different orientations of hexagonal axis is ...studied by simulation. The strain modification in the nonpolar and semipolar structures, as compared to polar ones, is found to result in both a higher indium percentage in the InGaN alloy and a larger materials bandgap, producing opposite trends in variation of the optical transition energy (emission wavelength) with the crystal orientation. The interplay between the effects is discussed in view of development of green‐light emitters. A possible way for controlling the strain in the InGaN layers and QWs and thus the emission wavelength is considered and tested by modelling.
Optical transition energy of the same single InGaN QW grown on either GaN or relaxed In0.08Ga0.92N sublayer as a function of the crystal C‐axis inclination to epitaxial layer plane.
Two-stage compression of laser pulses with a power of 250 TW is experimentally realised by broadening their spectrum during self-phase modulation in fused silica and subsequent dispersion ...compensation upon reflection from chirping mirrors. A five-fold decrease in the duration is demonstrated, from 75 to 15 fs, with a B-integral value of about 5 at each stage. It is possible to avoid small-scale self-focusing due to self-filtering of the laser beam during free propagation in vacuum. With optimal parameters of the dispersive mirror, the pulse can be compressed to a duration of less than 5 fs.
Compression of a 12-J laser pulse from 63 to 21 fs is experimentally demonstrated for a beam 18 cm in diameter. The compression is implemented for a pulse freely propagating in glass under conditions ...of self-phase modulation and subsequent compensation for dispersion under reflection from dispersion mirrors. This simple and inexpensive technique for increasing multiply the pulse power is characterised by almost 100 % energy efficiency and can be used at the output of any ultra-high-power laser, without any changes in its optical scheme.
Spectroscopic approaches are very good to noninvasively determine the most significant indicators of the tissue state. Indocyanine green (ICG) is a well-known fluorescent dye approved for clinical ...applications, which has a short circulation time in the vascular system and low photostability. At high temperatures the molecular solution of the photosensitizer self-assembles into a stable J-aggregate form of ICG nanoparticles (ICG NPs) with the absorption peak in the near-infrared range. Investigation of ICG NP stability in human blood and plasma using a fiber-spectroscopic system demonstrates no difference in absorption properties and different dependence of the integrated fluorescence ratio between ICG monomers and J-aggregates in blood and plasma. Transition of ICG NP aggregates to the monomeric form in human blood plasma results in a higher circulation time of the fluorescent dye in the vascular system. High stability of aggregates and a low elimination rate may increase efficiency of fluorescent diagnostics of near-tumor tissues.
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