Optical Pumping of Samarium Atoms in a Bichromatic Laser Field in the Presence of Velocity-Changing Collisions

Dark resonances in the ¹⁵⁴Sm -system 4f ⁶6s ²(⁷ F ₀) 4f ⁶6s6p(⁹ F ₁ ⁰) 4f ⁶ s ²(⁷ F ₁) are observed alongside the velocity selective optical pumping. The shape of the resulting spectra strongly depended on the buffer gas (He, Ar) pressure due to velocity-changing collisions (VCC): the sign of the effect could be reversed from the dark to the bright resonance. The observed spectra are interpreted within the framework of the hard-sphere collision model. The role of VCC in the formation of the dark state in the -system is discussed.     

Application of coherent four-wave mixing for two-dimensional mapping of the spatial distribution of excited atoms in a laser-produced plasma

An experimental technique for the two-dimensional mapping of the relative populations of excited states of atoms and ions in a low-temperature plasma of optical breakdown is developed on the basis of coherent four-wave mixing (FWM) with hyper-Raman resonances. The possibility to extract information concerning the spatial distribution of the populations of excited atomic and ionic states from two-dimensional maps of the FWM intensity allowing for phase mismatch and one-photon absorption is considered. Conditions when FWM in a plasma occurs in the phase-matched regime and is not subject to a considerable influence of one-photon absorption are experimentally determined.     

Infrared and EPR Spectroscopic Studies of 2-C(2)H(2)F and 1-C(2)H(2)F Radicals Isolated in Solid Argon

2-fluorovinyl radicals were generated in solid argon by solid-state chemical reactions of mobile F atoms with acetylene and its deuterated analogues. Highly resolved EPR spectra of the stabilized radicals CHF&dbond;(*)CH, CDF&dbond;(*)CD, CHF&dbond;(*)CD, and CDF&dbond;(*)CH were obtained for the first time. The observed spectra were assigned to cis-2-fluorovinyl radical based on excellent agreement between the measured (a(F) = 6.50, a(betaH) = 3.86, a(alphaH) = 0.25 mT) hyperfine constants and those calculated using density functional (B3LYP) theory. Analogous experiments carried out using infrared spectroscopy yielded a complete assignment of the vibrational frequencies. An unusual reversible photochemical conversion is observed in which cis-2-fluorovinyl radicals can be partially converted to 1-fluorovinyl radicals by pulsed laser photolysis at 532 nm. Photolysis at 355 nm converts 1-fluorovinyl back to cis-2-fluorovinyl. High-resolution EPR and infrared spectra of 1-fluorovinyl were obtained for the first time. The measured hyperfine constants (a(F) = 13.71, a(H1) = 4.21, a(H2) = 1.16 mT) are in good agreement with calculated values. Copyright 2001 Academic Press.     

Results of operating LIA-2 in radiograph mode

The LIA-2 linear induction accelerator was developed at the Budker Institute of Nuclear Physics as an electron beam injector for a building induction accelerator at energy of 20 MeV, on the basis of which a complex for flash radiography will be developed. The LIA-2, which was started up in 2010, is currently used as an independent X-ray unit for raying objects with an optic thickness up to 70 mm in the lead equivalent. The effective diameter of the X-ray source is 0.6–0.7 mm.     

Second-and third-harmonic generation by carbon nanotubes irradiated with femtosecond laser pulses

Femtosecond pulses of a Cr:forsterite laser are used to study second-and third-harmonic generation in a layer of single-wall carbon nanotubes produced by low-velocity spraying. The harmonic amplitude in our experiments scales as (I _p)ⁿ as a function of the pump intensity I _p, with n=2 and 3 for the second and third harmonics, respectively. This scaling law holds up to pump intensities on the order of 10¹²W/cm². The ratio of the maximum signal to the averaged background in the spectra of the second and third harmonics is estimated as 50 and 30, respectively. The second and third harmonics produced by a linearly polarized pump field are also linearly polarized, with their polarization vectors oriented along the polarization direction of the pump field. The capabilities of nonlinear-optical methods for structural and morphological analysis of carbon nanotubes are discussed, as well as ways to create solid-state carbon-nanotube generators of optical harmonic.     

Search for new phenomena in tt events with large missing transverse momentum in proton-proton collisions at sqrt[s] = 7 TeV with the ATLAS detector

A search for new phenomena in tt events with large missing transverse momentum in proton-proton collisions at a center-of-mass energy of 7 TeV is presented. The measurement is based on 1.04 fb(-1) of data collected with the ATLAS detector at the LHC. Contributions to this final state may arise from a number of standard model extensions. The results are interpreted in terms of a model where new top-quark partners are pair produced and each decay to an on-shell top (or antitop) quark and a long-lived undetected neutral particle. The data are found to be consistent with standard model expectations. A limit at 95% confidence level is set excluding a cross section times branching ratio of 1.1 pb for a top-partner mass of 420 GeV and a neutral particle mass less than 10 GeV. In a model of exotic fourth generation quarks, top-partner masses are excluded up to 420 GeV and neutral particle masses up to 140 GeV.     

Influence of the Structure of a Macromolecular System on the Processes of Association of Molecules of Rhodamine 6G in Aqueous‐Polyelectrolytic Solutions

The processes of association of rhodamine6G molecules in aqueous solutions of polyacrylic acid are studied by spectroscopic methods. The efficiency of formation of the dimers of rhodamine 6G as a function of the concentration of the polyelectrolyte and its chain length is established. The angles between monomer molecules in the dimers of rhodamine 6G are determined for different concentrations of the polyacrylic acid and lengths of the polyion chain.     

Influence of the size effect on the electrical conductivity of partially stabilized zirconia

The volume component of the electrical conductivity of bulk ceramics of the partially stabilized zirconia (ZrO₂)_0.94(Y₂O₃)_0.05(Al₂O₃)_0.01 is found to increase by a factor of 1.7 with the grain size decreasing from 600–800 to 200–300 nm. The observed effect is explained by the action of the pressure produced by surface tension forces, which shifts equilibrium toward the point of the polymorphic transition to the cubic phase.     

Ionic dissociation of CsBr induced by collisions with Hg: molecular-ion formation

The molecular complex formation (CF) reaction Hg+CsBr→HgCs⁺+Br⁻, competitive to the collision-induced dissociation (CID) Hg+CsBr→Hg+Cs⁺+Br⁻ was studied in crossed molecular beams. The rotatable mass-spectrometer detector made it possible to measure the branching ratio CID/CF in the translation energy range between 5.2–7.9 eV, as well as the angular and energy distributions of positive ions. The branching ratio is an order of magnitude greater than for the Xe+CsBr reaction. HgCs⁺ ions were found only to backscatter. A 2D impulsive model shows two distinct reactive geometric configurations, which both lead to backscattering. The key role of the internal molecular motion is also predicted by the impulsive model.