ALBERT

Description: Systematic numerical study of near-infrared radiation formed during filamentation in air revealed the formation of robust light bullet first registered in the experiment (Chen et al. in Appl Phys B 91:219, 2008 ). The near-infrared light bullet propagates along the filament axis with the divergence 〈1 mrad and the quasi-constant duration of ~30 fs. The central wavelength of the bullet gradually increases from 860 to 900 nm during the propagation. The results of our numerical simulation are in agreement with the experiments (Chen et al. in Appl Phys B 91:219,  2008 ; Uryupina et al. in Appl Phys B 110:123, 2013 ).

Description: Flame flatness is one of the most critical factors in evaluating the performance of a flat-flame burner. In this paper, the flame flatness of a flat-flame burner is validated using a resolution-doubled one-dimensional wavelength modulation spectroscopy tomography (1D-WMST) technique that only uses one view of multiple parallel laser beams. When the interval of two neighboring parallel laser beams is Δ r , a designed novel geometry of the parallel laser beams realizes a doubled tomographic resolution of Δ r /2. Using the proposed technique, the distributions of temperature and H 2 O mole fraction in an axisymmetric premixed flame are simultaneously reconstructed and hence the flame flatness of a flat-flame burner can be validated. The flatness factor is quantitatively described by the similarity between the reconstructed and expected distributions of H 2 O mole fraction. For flat and non-flat flames, the experimental results agree well with the CFD simulation results, denoting that the resolution-doubled 1D-WMST technique provides a noninvasive, reliable and low cost way to validate the flame flatness of the flat-flame burner.

Description: We report on the optical performances of laccaic acid dye in solution at different concentrations and dye–poly(methyl methacrylate) composite thin films. The linear spectral characteristics including optical constants, i.e. refractive index ( n ) and extinction coefficient ( k ), were carried out in a comprehensive way through absorbance, fluorescence and ellipsometric studies. The nonlinear optical parameters such as nonlinear absorption coefficient β eff (or β 2 ), the imaginary third-order susceptibility (Im[ χ (3) ]) and the imaginary part of second-order hyperpolarizability ( γ ) of the samples were evaluated using the open-aperture Z-scan technique with a laser pulse duration of 10 ns at 532 nm wavelength. The corresponding numerical values of these parameters were of 10 −10 , 10 −11 and 10 −32 order, respectively. Two-photon absorption was revealed to be the main driving physical mechanism in the nonlinear response. This suggests that laccaic acid dye can be a potential candidate for NLO materials application.

Description: We demonstrate a sensor based on tunable diode laser absorption spectroscopy for the detection of hydrogen fluoride (HF) gas at ambient pressure. Absorption from the HF R(1) ro-vibrational peak at ν̃  = 4038.962 cm −1 (2.476 µm) in the fundamental (Δ ν  = 1) band is measured. A quantitative spectral fit based on HITRAN data is used to account for overlapping spectral peaks of HF and water vapor, with an rms residual noise of 5 × 10 −4 absorbance units. The sensor is optimized for the detection of transient variations in HF concentration. We measure noise-equivalent concentrations for HF of 38 parts-per-trillion by volume (ppt) for 1-s integration times and 2.3 ppt for 10-min integration times.

Description: We report on the absorption profile of the monoclinic holmium-doped \(\hbox {KY}(\hbox {WO}_4)_2\) crystal near the optic axis for the maximal absorption wavelength at 1960 nm. The full angular distribution of the absorption coefficient at the vicinity of such optical singularity has been experimentally and numerically investigated. Furthermore, laser experiments along the optic axis have been carried out. So-called conical refraction laser and classical Gaussian laser operation are compared near the optic axis, taking into account the complex absorption profile.

Description: We demonstrate a novel and compact fiber-probe pressure sensor based on a micro-Fabry–Perot interferometer (FPI). The device is fabricated by splicing both ends of a short-section simplified hollow-core photonic crystal fiber (SHC-PCF) with single-mode fibers. Then, a microchannel is drilled by a femtosecond laser micromachining in the SHC-PCF to allow air to diffuse in. The pressure sensing mechanism is based on the dependence of the air refractive index on pressure. We use both theory and experiment to investigate the sensing characteristics. A micro-FPI with a length of 272 μm demonstrates a pressure sensitivity of 4.071 nm/MPa at 1580 nm and a low-temperature sensitivity of 1.1 pm/°C at atmospheric pressure. We further study the temperature cross sensitivity of the sensor under different pressures. The sensor also shows strong stability and good reversibility, and may be potentially used in pressure sensing applications.

Description: We study the thermo-optic Goos–Hänchen (TOGH) effect in a prism–waveguide coupling structure with silicon-on-insulator waveguide. Stationary-phase method is utilized to calculate the TOGH shift. When the waveguide is regarded as a two-dimensional planar waveguide, a nonlinear relation between GH shift and temperature is obtained. Based on the noticeable TOGH effect, a sensitive temperature modulator or sensor can be realized. As the waveguide width is limited, the proposed structure can be regarded as a three-dimensional rectangular waveguide. We explore the GH shift and TOGH effect for different modes propagating in rectangular waveguide which show different linear relations between GH shift and temperature, which can be used to design mode-selective device based on TO effect.

Description: We report on an experimental study of vacuum-induced suppression and enhancement of four-wave mixing (FWM) signal in a composite atom–cavity system. By scanning the additional dressing field, the suppression ratio of the FWM signal can reach 90 % compared with 40 % without cavity. We attribute the enhanced suppression and enhancement to the atom–cavity coupling arising from a vacuum-induced Raman process, which amplifies the dressing effect from the additional field. Also, the dressing asymmetry of the atom–cavity coupling is discussed and used to estimate the nonlinearity of atomic medium in the cavity. The suppression and enhancement can be interpreted by a dressed-state picture and agree with theoretical calculations. The investigation may find applications in optical switch and quantum memory controlled by cavity.

Description: By simultaneously using a multi-walled carbon nanotube (MWCNT) and a monolayer graphene saturable absorber (SA) in the cavity, a laser-diode-pumped dual-loss-modulated passively Q-switched Tm:LuAG laser at 2 μm is demonstrated for the first time. In comparison with the singly passively Q-switched laser with MWCNT or monolayer graphene SA, the doubly passively Q-switched laser with both MWCNT and monolayer graphene SA can generate shorter pulse width and higher peak power. A maximum pulse width compression ratio of 2.8 and a highest peak power enhancement factor of 4 were obtained at the incident pump power of 5.8 W, respectively. The experimental results show that the dual-loss modulation is an efficient method to compress the pulse widths and improve the peak powers of the Q-switched lasers at 2 μm.

Description: Photoexcitation dynamics in a three-step photoionization of atomic uranium has been investigated using time-resolved two-color three-photon and delayed three-color three-photon photoionization signals. Investigations are carried out in an atomic beam of uranium coupled to a high-resolution time-of-flight mass spectrometer using three tunable pulsed dye lasers. Dependence of both the signals on the second-step laser photon fluence is studied. Excited-level-to-excited-level photoexcitation cross section and photoionization cross section from the second excited level are simultaneously determined by analyzing the two-color three-photon and three-color three-photon photoionization signals using population rate equation model. Using this methodology, photoexcitation and photoionization cross sections at seven values of the second-step laser wavelength have been measured. From the measured values of the photoexcitation cross sections, we have obtained excited-level-to-excited-level transition probabilities and compared these with the values reported in the literature.

Description: The topology and conditions of nucleation of magnetic inhomogeneities at defects of a uniaxial ferromagnet have been investigated theoretically. It has been shown that, for specific material parameters, two types of inhomogeneities corresponding to a 0-degree domain wall, which differ in the size, amplitude, and energy, can arise at defects. It has been found that the large-amplitude inhomogeneity is a metastable formation. However, with inclusion of demagnetizing fields of the sample, it can become stable, i.e., energetically more favorable in comparison with the small-amplitude inhomogeneity. The possible contribution from this inhomogeneity to the static and dynamic processes of magnetization reversal of magnetic materials has been considered.

Description: This paper presents the results of investigations of the ordering of Jahn-Teller distorted MnO 6 octahedra in lightly doped single crystals of the composition La 1 − x Sr x MnO 3 (0.12 〈 x 〈 0.175) using the complex technique including measurements of elastic moduli and damping of high-frequency acoustic waves (700 MHz), electrical conductivity as a function of the temperature (100–400 K), and magnetic field ( H ≤ 1.5 T). The self-organization of the orbital, magnetic, and Jahn-Teller orderings and their influence on the transport, magnetic, and structural properties of lightly doped manganites have been investigated based on the analysis of the experimental results. The decisive influence of the local and cooperative Jahn-Teller orderings on the colossal magnetoresistance effect has been established.

Description: This paper presents the results of investigations of the structure, phase composition, and spectral-luminescent properties of Er 2 O 3 -doped zirconia crystals with different Y 2 O 3 concentrations: 99.7 mol % ZrO 2 -0.3 mol % Er 2 O 3 , 97.2 mol % ZrO 2 -1.0 mol % Y 2 O 3 -1.8 mol % Er 2 O 3 , 97.2 mol % ZrO 2 -2.0 mol % Y 2 O 3 -0.8 mol % Er 2 O 3 , 97.2 mol % ZrO 2 -2.5 mol % Y 2 O 3 -0.3 mol % Er 2 O 3 , 96.3 mol % ZrO 2 -3.4 mol % Y 2 O 3 -0.3 mol % Er 2 O 3 , and 86 mol % ZrO 2 -13.4 mol % Y 2 O 3 -0.6 mol % Er 2 O 3 . The transmission electron microscopy investigation has revealed the presence of twins in the 99.7 mol % ZrO 2 -0.3 mol % Er 2 O 3 crystals with a monoclinic structure and in the 97.2 mol % ZrO 2 -2.5 mol % Y 2 O 3 -0.3 mol % Er 2 O 3 and 96.3 mol % ZrO 2 -3.4 mol % Y 2 O 3 -0.3 mol % Er 2 O 3 crystals with a tetragonal structure. No twins have been found in the 86 mol % ZrO 2 -13.4 mol % Y 2 O 3 -0.6 mol % Er 2 O 3 crystals with a cubic structure. The phase composition of these crystals has been investigated using X-ray diffraction. It has been found that the 97.2 mol % ZrO 2 -1.0 mol % Y 2 O 3 -1.8 mol % Er 2 O 3 crystals contain only the transformable tetragonal phase t , whereas the 97.2 mol % ZrO 2 -2.0 mol % Y 2 O 3 -0.8 mol % Er 2 O 3 , 97.2 mol % ZrO 2 -2.5 mol % Y 2 O 3 -0.3 mol % Er 2 O 3 , and 96.3 mol % ZrO 2 -3.4 mol % Y 2 O 3 -0.3 mol % Er 2 O 3 crystals include two tetragonal phases with different degrees of tetragonality c / a : the transformable phase t and nontransformable phase t ′. Specific features of the formation of Er 3+ optical centers in zirconia crystals with different concentrations of stabilizing oxides have been revealed using the results of experiments on optical spectroscopy.

Description: The results of the experimental observation of the photovoltage in a SrTiO 3 crystal sample, which exhibits the light-induced resistance-drop effect, have confirmed the previously proposed model of the effect in its photoelectric part. However, in addition to the expected manifestation of the barrier photovoltage, one more source of photocurrent has been found. This source is attributed to the manifestation of the linear photogalvanic effect in the subsurface region of the crystal. It has been assumed that the main role in the generation of photogalvanic current can be played by dipole centers of the oxygen vacancy-triply charged titanium ion type, which are oriented by an electric field of the surface barrier.

Description: The results of investigations of the morphological properties of an oxide film formed on single-crystal silicon by anodic oxidation in distilled water in the potential-controlled mode have been presented. It has been established that the oxide film is always formed in the form of separate islands, the shape of which depends on the substrate orientation irrespective of the applied potential.

Description: The elastic hysteresis and residual deflections of samples made of steel 20, which correspond to the model of a thin rigid round plate pinched over the contour, have been investigated. It has been shown that annealing of the samples at 470 and 670 K weakly affects these characteristics, while after complete annealing (1170 K), the aging of steel 20 for three days is accompanied by a decrease in amplitude ω h of the elastic hysteresis by ∼20%. A postulate that there is no elasticity limit of metals, below which residual deformation would be absent, has been confirmed experimentally. It has been shown that, based on the values of ω h , the ultimate strength of metals can be estimated acting on the samples by stresses smaller than the yield stress by an order of magnitude. A giant increase (by a factor of ∼2.5) in ω h has been found after a prolonged (for 2 months) aging of steel 20 after the diffusion of hydrogen from it, which indicates the corresponding decrease in its cyclic longevity.

Description: A series of jumps of the magnetic moment (up to five jumps) with an amplitude of 1–10% of the saturation magnetization has been observed upon demagnetizing the molecular magnet [Mn{( R / S )- pn }] 2 [Mn{( R / S )- pn } 2 (H 2 O)][Cr(CN) 6 ] 2 in a narrow region of magnetic fields close to the coercive force. A decrease in the temperature leads to an increase in the critical magnetic field, which corresponds to the onset of the series of demagnetization jumps. The obtained experimental data agree with theoretical predictions on jump-like transitions between the magnetization curves upon attaining critical magnetic fields caused by the energy quantization of spin solitons.

Description: A theoretical analysis of the photorefractive sensitivity of Ti:PPLN ridge waveguides in comparison with conventional Ti:PPLN channel waveguides is presented. In particular, intensity-dependent photorefraction, effective indices, waveguide modes and power-dependent SHG in Ti:PPLN ridge and channel waveguides are modeled for a wide range of parameters. Results predict a much better damage resistance of Ti:PPLN waveguides with ridge geometry in comparison with conventional indiffused channels. This superiority of ridge waveguides is attributed to their higher effective refractive index contrast and more tightly confined guided modes. The theoretical predictions are supported by experimental results for second harmonic generation (SHG) at room temperature and for light-induced detuning characteristics of the phase-matching wavelength.

Description: Magnetic properties of cobalt atoms in Au-Co chains on the Cu(110) surface (such as the magnetic moment, magnetic anisotropy energy, and exchange energy) have been calculated in the framework of the density functional theory. It has been found, at zero temperature, an infinitely long Au-Co chain is in the ferromagnetic state. The magnetostatic and magnetodynamic properties of finite-length Au-Co chains at a nonzero temperature have been investigated within the Heisenberg model using the kinetic Monte Carlo method. The dependences of the Curie temperature and magnetization reversal time on the chain length have been obtained, as well as the dependences of the coercivity of the chain on the temperature, chain length, and magnetization reversal rate.

Description: The influence of precipitation of germanium atoms in a solid solution on the dependence of the inelasticity characteristics on the germanium content in aluminum-germanium alloys prepared by directional crystallization has been studied. It has been shown that the Young’s modulus defect, the amplitude-dependent decrement, and the microplastic flow stress at a specified cyclic strain amplitude have extreme values at the eutectic germanium content in the alloy. The eutectic composition of the alloy undergoes a ductilebrittle transition. It has been found that there is a correlation between the dependences of the Young’s modulus defect, amplitude-dependent decrement, microplastic flow stress, and specific entropy of the exothermal process of germanium precipitation on the germanium content in the hypoeutectic alloy. The concentration dependences of the inelasticity characteristics and their changes after annealing have been explained by the change in the resistance to the motion of intragrain dislocations due to different structures of the Guinier-Preston zones formed during the precipitation of germanium atoms.

Description: The correlation of the electrical, magnetic, and structural properties of B i2 (Sn 1 − x Cr x ) 2 O 7 solid solutions has been investigated for two compositions with x = 0.05 and 0.1. The temperatures of structural phase transitions and anomalies of the electrical resistance in the vicinity of these transitions at temperatures in the range 300 K 〈 T 〈 1000 K have been determined using differential scanning calorimetry. It has been found that the thermoelectric power changes sign upon the polymorphic transition. The paramagnetic Curie temperature and the chromium-ion spin have been found from the temperature dependence of the magnetic susceptibility in the range 4 K 〈 T 〈 1000 K and from the field dependence of the magnetic moment in magnetic fields of up to 6 T.

Description: It has been shown experimentally that the thermal dissolution of silver and gold thin films in silicate glass is accompanied by the formation of a monolayer of silver and gold micro- and nanocrystals, respectively, on the surface of the glass. These processes occur at temperatures well below the melting temperature of the metal. Microcrystals are formed predominantly at the edges of islands of the metal film, where there is a sufficient amount of the material for their growth. Silver and gold nanocrystals are formed in the case when atoms of the metal dissolved in the glass repeatedly emerge on the glass surface. Silver and gold dissolved in the glass exist not only in the form of atoms and ions but also in the form of charged and neutral molecular clusters.

Description: Cooling of metallic glasses based on Pd and Zr from the supercooled liquid state with a low rate causes significant shear modulus and internal friction hystereses, which indicates a long relaxation time in the vicinity of the glass transition range. The nature of the observed phenomenon has been discussed within the interstitialcy theory.

Description: The effect of the linear approximation of the electronic spectrum of single-layer graphene (low-energy approximation) on the magnitude of charge transfer between an adatom and graphene has been investigated. It has been shown that the implementation of this approximation for adsorption of alkali metals and halogens leads to a change in the occupation numbers of local and band states as compared to the results obtained in the model taking into account the entire spectrum. However, the total occupation numbers agree quite well.

Description: The effect of pressure up to 22 GPa on the electrical resistance and thermopower of lanthanum monobismuthide at room temperature has been studied. A semiconductor-metal phase transition in the pressure range of 4–6 GPa has been revealed from the change in the sign of thermopower and the thermal dependence of the electrical resistance of LaBi. The observed inflections in the pressure dependences of the thermopower and electrical resistance of LaBi samples in the pressure range of 8–11 GPa can be ascribed to the structural phase transition from the B 1 phase to the PT and B 2 phases.

Description: Results of X-ray diffraction studies of shock-compressed single crystals indicate the rotation of crystallites by ∼3° ahead of the shock-wave front both in the plastic-flow and elastic-compression regions. Two dynamic states of the lattice have been detected. The brightness of reflections evolves with time. The position of the first dynamic reflection coincides with the position of a reflection from the initial structure. The second reflection corresponds to an equilibrium-compressed structure. Possible reasons of the formation of these two states of the lattice have been discussed.

Description: The growth and crystal structure of NiF 2 layers on CaF 2 /Si(111) heteroepitaxial substrates have been investigated. It has been shown that molecular beam epitaxy at temperatures of 350–450°C provides a stable epitaxial growth of the metastable orthorhombic NiF 2 phase (structural type CaCl 2 ) with a nickel fluoride layer thickness up to 1 μm in the metastable phase. According to X-ray diffraction, the unit cell parameters in layers of orthorhombic nickel fluoride are a = 4.5680(1) Å, b = 4.7566(3) Å, and c = 3.0505(2) Å, which are very close to the known values for this phase. It has been established that the condition \((100)_{NiF_2 } \left\| {(111)_{CaNiF_2 } } \right.\) holds over a wide range of growth parameters, which agrees with the results of the qualitative crystallographic analysis of the elements of similarity of the structures under consideration. The formation of a domain texture, the character of which depends on the growth temperature and nickel fluoride layer thickness, has been observed in the heterojunction plane.

Description: Two-color laser-induced incandescence (LII) measurements are carried out in diffusion flames and at the exhaust of a homemade soot generator, both fueled with ethylene and methane. Two-color prompt LII signals, their ratio and the corresponding temperature have been analyzed as a function of laser fluence. In particular, the effect of fuel, soot load and gas/particle initial temperature on LII measurements have been investigated. LII spectral measurements have also been performed in all conditions for validation. The results suggest that the incandescence is sensitive to both optical and non-optical physical properties of the particles. Moreover, soot volume fraction measurements are dependent on the laser fluence used, indicating that the soot temperature influences the refractive index absorption function. Such issues can be overcome by working at high laser fluences, where the saturation curves are independent from the experimental conditions if the soot absorption function near soot sublimation threshold is known.

Description: The problem of adsorption on amorphous single-layer graphene whose density of states is described by a simple analytic model has been considered. An analytic expression has been obtained for the density of states on the adatom. The estimations for the adsorption of H, K, Rb, and Cs show that the charge transfer from an adatom to the substrate in the case of the ideal single-layer graphene is higher than that in the case of amorphous graphene.

Description: A dislocation kinetic model of the formation and propagation of plastic shock waves in nanocrystalline materials (with a grain size of 1–100 nm) at pressures ranging from 1 to 50 GPa has been discussed theoretically. The model is based on a nonlinear equation of the reaction-diffusion type for the dislocation density, which includes the processes of multiplication, annihilation, and diffusion of dislocations with a strong absorption of the dislocations by nanograin boundaries. The solution of this equation is obtained in the form of a traveling dislocation density wave propagating with a constant velocity. The dependences of the dislocation density and dislocation front width on the nanograin size and pressure in the wave are determined. A comparison of the obtained dependences with the available results of the experiments and molecular dynamics simulations of shock-deformed nanocrystalline materials demonstrates their good quantitative agreement.

Description: The effect of the interface on the electrical resistance of graphene chemically deposited from the gas phase (CVD graphene) has been studied in the range from room temperature to the nitrogen boiling temperature. The resistance of a single-layer CVD graphene in the cases of its contacting with Si/SiO 2 and GaAs substrates demonstrates a nearly linear metallic temperature dependence with almost the same slope of the normalized curves. This slope corresponds to an increase in the graphene resistance by ~8% when graphene is heated from the boiling nitrogen temperature to room temperature. The four-layer graphene demonstrates a semiconducting temperature dependence in the same temperature range. It has been found that the sputtering of an organic insulator (parylene) on the four-layer graphene increases the slope of this dependence by ~5% and, at room temperature, increases the graphene resistance by ~20%.

Description: The ab initio calculation has been performed for the crystal structure and the phonon spectrum of titanates with the structure of pyrochlore R 2 Ti 2 O 7 ( R = Gd-Lu). The frequencies and types of fundamental vibrations have been found. For R = Tb, Tm, and Yb, this calculation has been carried out for the first time; furthermore, there is no available information on experimental studies of the phonon spectrum for Tm and Yb. The influence of hydrostatic pressure to 35 GPa on the structure, dynamics, and elastic properties of the Gd 2 Ti 2 O 7 lattice has been investigated. The dependence of the phonon frequencies on the pressure has been obtained. The calculations have predicted that the relative change in the pyrochlore structure volume during compression at pressures to 35 GPa is well described by the third-order Birch-Murnaghan equation of states. The results of the calculations agree with the available experimental data. It has been shown that the structural, dynamic, and elastic properties of the R 2 Ti 2 O 7 crystal lattice can be adequately described in the case where the inner shells of the RE ion up to 4 f are replaced by the pseudopotential.

Description: An analytical expression for the relaxation constant α in the Landau-Lifshitz-Hilbert equation has been derived using the semiclassical kinetic equation for the distribution function of magnons.

Description: The effect of constant magnetic fields on dislocation anharmonicity of p -type silicon single crystals with a conductivity of 6 Ω cm has been studied. It has been found that preliminary exposure of dislocation silicon (with a dislocation density of 10 4 –10 6 cm −2 ) to a constant magnetic field ( B = 0.7 T, t = 30 min) at room temperature causes a change in the nonlinear fourth-order elastic modulus β d . The observed changes are associated with the dynamics of magnetosensitive complexes of structural defects and, hence, with the changes in the length of the vibrating dislocation segment. Based on the dynamics of β d ( t ) after sample exposure to a magnetic field, the conclusion is made about an increase in the vibrating dislocation segment length L d by 30%, and the characteristic relaxation times of observed effects are estimated.

Description: The results of quantum-mechanical calculations of elementary prismanes—hexaprismane C 12 H 12 and octaprismane C16H16—have been presented. Their stability has been investigated in terms of the density functional theory and nonorthogonal tight-binding model, and the heights of potential barriers preventing isomerization and decay have been determined. It has been established based on the analysis of the molecular dynamics data and the hypersurface of the potential energy of these metastable compounds that hexaprismane and octaprismane have a rather high kinetic stability, which indicates the possibility of the formation of carbon polyprismanes for applications in microelectronics and nanoelectronics, power engineering, pharmaceutics, metrology, and information technologies.

Description: A radically new percolation model for describing the extremal dependence of the degree of reinforcement of polymer/carbon nanotube nanocomposites on the nanofiller content has been proposed. It has been shown that, for this nanofiller, the percolation threshold almost coincides with the aggregation threshold on the concentration scale. From the structural point of view, the extremum of this dependence is caused by the change in the type of the reinforcing component (from interphase regions to the skeleton of carbon nanotubes). From the mathematical point of view, the behavior of the degree of reinforcement is described by the general percolation relationship with replacement of the critical exponents near the percolation threshold. Neither the functionalization of the nanofiller nor the preliminary ultrasound treatment qualitatively change the dependence under study.

Description: The results of ab initio calculations of the ferroelectric and magnetic properties of the recently synthesized double perovskites LaPb Me SbO 6 ( Me 2+ = Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ ) have been presented. The ordered double perovskites with a layered ordering of cations A and A ′ and a checkerboard ordering of cations B and B ′ have been considered. The calculation of the lattice dynamics has revealed instabilities in the phonon spectra of the high-symmetry phase of these compounds. The condensation of unstable modes leads to a stable polar phase P 2 1 . The spontaneous polarization in this phase is found to be ~30 μC/cm 2 . The magnetic ground state is antiferromagnetic with an antiparallel direction of the magnetic moments in adjacent planes along the [001] direction. The Néel temperatures are estimated in the mean field approximation. The presence of the ferroelectric and magnetic order parameters in the structure suggests that the studied double perovskites with the simultaneous ordering of the cations are potential multiferroics.

Description: The Bethe approximation as applied to a system consisting of magnetic and nonmagnetic atoms in the thermodynamic equilibrium has been considered. In this approximation, the dependences of the magnetization and Curie temperature on the concentration of magnetic atoms for the Ising model with mobile nonmagnetic impurities have been constructed and the limiting concentrations of the appearance of spontaneous magnetization in the ground state have been obtained. It has been established that the considered approximation for a one-dimensional chain is the exact solution.

Description: The effects of the interaction of ultrasound with donor d electrons of cobalt impurity atoms at low concentrations in mercury selenide crystals have been investigated. The temperature dependences of the electronic contribution to the absorption coefficient at a frequency of 53 MHz in crystals with cobalt concentrations from 10 18 to 10 20 cm −3 and in the undoped crystal have been observed experimentally. It has been found that crystals with impurities are characterized by an anomalous nonmonotonic temperature dependence of the absorption coefficient of the slow transverse wave in a narrow temperature range near 10 K. A smooth monotonic temperature dependence has been observed for longitudinal and fast transverse waves. Based on the developed theoretical interpretation, it has been established that the anomaly in the temperature dependence of the absorption coefficient of a slow transverse wave is associated with the hybridization of impurity d states in the conduction band of the crystal. A comparison of the theoretical and experimental dependences has made it possible to determine the parameters characterizing the hybridized electronic states.

Description: The effect of the accelerating voltage U of the SEM electron beam on the characteristics of microdomains recorded by the electron beam method on the nonpolar Y -surface of LiNbO 3 crystals has been studied. The thickness T d of domains in the Y direction is determined by the depth range R e of primary electrons, which depends on U . This makes it possible to define T d in the range of 0.2–4 μm at U = 5–25 kV, respectively. The electron emission coefficient σ is estimated for different values of U exceeding the second equilibrium point U 2 (σ = 1) in the σ( U ) diagram. These data are used to construct the dependence σ( U ) for LiNbO 3 . Based on the exposure characteristics of the length L d of domains growing along the polar Z axis, the dependence of the space charge field controlling the domain planar growth along Z on the surface electron emission σ is found.

Description: It has been found that the phase with the fcc lattice of the NaCl structural type is formed due to the vacuum-arc deposition of the nanostructured multicomponent (TiZrHfVNbTa)N coating. Implantation of negative Au − ions with a dose of 1 × 10 17 cm −2 leads to the formation of a disordered polycrystalline structure without a preferred orientation of the fcc phase and nanocrystallites from 5–7 to 1–3 nm is size, which are dispersed in a layer up to 35 nm in depth. Nanohardness increases to 33 GPa, and the Vickers hardness reaches 51 GPa. Gold nanoclusters are formed in the near-surface region, while the fcc lattice and the formation of local Au regions are observed in the coating itself. Fragments with the hcp lattice are formed at depths above 180 nm because of the low nitrogen concentration.

Description: Based on the numerical solution of Landau-Lifshitz equations, the nonlinear dynamic behavior of vortex-like domain walls in films with in-plane anisotropy has been investigated in external magnetic fields H significantly exceeding critical fields H c , above which the stationary motion of domain walls is replaced by nonstationary (periodic or aperiodic) motion. A method has been proposed for the detection of complex aperiodic dynamics of structural rearrangements of domain walls, which is based on the construction of diagrams of the dependences of the tilt angle of the magnetization M with respect to the plane of the domain wall in some of its points on the corresponding angle in other points. It has been found that these diagrams significantly change with variations in the external magnetic field applied along the easy axis of magnetization in the range H 〉 H c . It has been shown that the pattern of these changes is similar to the scenario of the Feigenbaum transition to dynamic chaos.

Description: The correlation between the heat capacities of rare-earth cuprates, orthovanadates, and garnets with ionic radius R 3+ has been analyzed. It has been shown that the values of C p 0 change consistently depending on the radius R 3+ within the corresponding tetrads (La-Nd, Pm-Gd, Gd-Ho, Eu-Lu).

Description: Relaxation processes in side-chain liquid-crystal azomethine polymer have been studied using dielectric spectroscopy in wide ranges of temperatures and frequencies. Two low-temperature relaxation processes (β 1 and β 2 ) caused by low-amplitude noncooperative motion of kinetic units in side groups and a high-temperature α-process caused by the large-scale cooperative motion of kinetic units in the main polymer chain have been revealed.

Description: In this study, In 2 O 3 /Ag/MoO 3 (IAM) nano-multilayer films are designed, and optimum thickness of each layer is calculated. These films were deposited by thermal evaporation technique and then annealed in air atmosphere at different temperatures for 1 h. The effects of annealing temperature on electrical, optical, and structural properties of the IAM system were investigated. The UV–visible–near-IR transmittance and reflectance spectra confirmed that the annealing temperature has significant influence on the electro‐optical characteristics of IAM films. High-quality IAM films with a low sheet resistance of 8.2 (Ω/□) and the maximum optical transmittance of 85 % at 120 °C annealing temperature were obtained. The effect of heat treatment on surface roughness of the layers was also investigated. Figure-of-merit quantity showed that the IAM films annealed at 120 °C have the best performance. X-ray diffraction patterns showed that the crystallinity of the structures enhanced with increase in annealing temperature. Organic light-emitting diodes (OLEDs) were fabricated on IAM anodes. The current density–voltage–luminance (J–V–L) characteristic measurements show that the electroluminescence performances of OLED with IAM anode are improved compared with the conventional ITO-based device. The results indicate that the designed system is suitable for use as transparent conductive anode in optoelectronic devices.

Description: We demonstrate the effectiveness of silicon phase masks to implement spatially resolved, multispectral imaging capabilities in the range of terahertz frequencies, using a standard setup of basic interest for time-domain spectrometry with a single-cell source and a single-cell detector. Our principle primarily aims at the development of robust and inexpensive systems. It consists of appropriate space-to-time encoding, in order to ensure single-scan triggering and then take advantage of rapid and self-consistent measurements in the two-dimensional space. The process enables very efficient discrimination giving access to a relevant spatial resolution in the analysis of small size, planar assemblies made of inhomogeneous materials. Benchmark results are provided to validate the concept, thanks to prototyping phase masks with 2 × 2 pixels, prior evidencing actual performance limitations in the case of 3 × 3 pixels. Due to the frequency bandwidth of 0.1–1.5 THz in our setup and to the available operating conditions, currently acceptable pixel resolutions lie in the range of 3–4 mm. Numerical modeling by means of finite elements helps to discuss these numbers and to investigate the relevant theoretical issues, figuring the main propagation issues in connection with a sub-picosecond seed pulse throughout various masks. This involves diffraction and trailing edge effects when crossing the mask together with residual, parasitic reflections. Finally, we give a consistent prospective for improved performance, via realistic updates regarding the architecture of the setup and complementary post-processing. Further values for the attainable spatial resolution then range from 5 × 5 to 6 × 6 pixels.

Description: A combination of optical emission spectroscopy (OES) and cavity ring-down spectroscopy (CRDS) has enabled to determinate the number densities of CH(A 2 Δ) and CH(X 2 Π) radicals simultaneously in a cascaded arc plasma reactor operating with a CH 4 /Ar mixture. It is found that the number density of CH(A 2 Δ) radical increases with discharge current at first and then decreases. However, the number density of CH(X 2 Π) radical decreases with discharge current when the rate of CH 4 flow to total flow is lower than 1 %, while it increases slightly with discharge current when the rate is 1.5 %. The results reveal that CH radicals are deviation from excitation equilibrium. Although OES is the simplest and most straightforward means to investigate the CH radical behavior, it is not enough to provide the information of the CH(X 2 Π) number density, and additional methods, such as CRDS, are needed in the cascaded arc plasma jet.

Description: In this paper, we present a numerical study based on 3D FDTD (finite-difference time-domain) simulations that demonstrate the high sensitivity of the optical response of a bowtie nano-aperture antenna (BNA), engraved at the apex of a metal-coated tip, to the distance variation between it and a given substrate. This study mainly discussed the case of the collection mode regime of the BNA and considered the case of two different substrates (high and low refractive index). The coupling between the substrate and the BNA may greatly affect the properties of the optical resonance of the nano-antenna. A blueshift of the resonance wavelength, as large as \(\frac{\varDelta \lambda }{\lambda }=0.3\) , is obtained when the tip moves away over only 10 nm from the substrate (InP) interface. These results open the way to the design of stand-alone optical near-field probes that allow faithful interaction control with a given sample as a function of the distance between them.

Description: The present paper describes the research of the optical device for two-dimensional straightness measurement of technological machines. Mathematical study of an optical device, operating on the phase principle and measuring transversal displacements of machine parts in two directions ( X and Y ) during their linear longitudinal motion in a machine (alongside the Z axis), is presented. How to estimate the range of travel along the Z axis is analytically shown. At this range, the measurer gives correct measurements of transverse displacement. The necessary distance from the objective focus to the image plane was defined mathematically. The sample results of measuring the displacement of the table of a technological machine by using the optical device are presented in the paper. This optical device for non-contact straightness measurement can be used for measurement straightness in turning, milling, drilling, grinding machines and other technological machines, also in geodesy and cartography, and for moving accuracy testing of mechatronic devices, robotics and others.

Description: Non-resonant laser-induced thermal acoustics (LITA), a four-wave mixing technique, was applied to post-shock flows within a shock tube. Simultaneous single-shot determination of temperature, speed of sound and flow velocity behind incident and reflected shock waves at different pressure and temperature levels are presented. Measurements were performed non-intrusively and without any seeding. The paper describes the technique and outlines its advantages compared to more established laser-based methods with respect to the challenges of shock tube experiments. The experiments include argon and nitrogen as test gas at temperatures of up to 1000 K and pressures of up to 43 bar. The experimental data are compared to calculated values based on inviscid one-dimensional shock wave theory. The single-shot uncertainty of the technique is investigated for worst-case test conditions resulting in relative standard deviations of 1, 1.7 and 3.4 % for Mach number, speed of sound and temperature, respectively. For all further experimental conditions, calculated values stay well within the 95 % confidence intervals of the LITA measurement.

Description: Airflow induced by femtosecond laser (800 nm/1 kHz/25 fs) filamentation with different lengths was investigated in a laboratory cloud chamber. Various filament lengths were generated by adjusting laser energy and lens focal length. It was found that airflow patterns are closely related to filament intensity and length. Intense and long filaments are beneficial in updraft generation with large vortices above the filament, while intense and short filaments tend to promote the formation of well-contacted vortices below the filament. Differently patterned airflows induced elliptical snow piles with different masses. We simulated airflow in a cloud chamber numerically taking laser filaments as heat sources. The mechanisms of differently patterned airflow and snow formation induced by filaments were discussed.

Description: Tissue simulators, the so-called tissue phantoms, have been used to mimic human tissue for spectroscopic applications. Phantoms’ design depends on patterning the optical properties, namely absorption and scattering coefficients which characterize light propagation mechanisms inside the tissues. In this work, two calibration models based on measurements adopting integrating sphere systems have been used to determine the optical properties of the studied solid phantoms. Integrating sphere measurement results were fed into the calibration models using the multiple polynomial regression method and Newton–Raphson algorithm. The third-order polynomials have been used for optical properties predictions. Good agreement between the two models has been obtained. Role of solid phantoms’ components, namely titanium dioxide as a scatterer and black carbon as an absorber, has been discussed. Both of the two components showed observable effects on the absorption and scattering of light inside the solid tissue phantoms.

Description: We report a novel time-resolved photoacoustic-based technique for studying the thermal decomposition mechanisms of some secondary explosives such as RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), picric acid, 4,6-dinitro-5-(4-nitro-1 H -imidazol-1-yl)-1 H -benzo[ d ] [ 1 – 3 ] triazole, and 5-chloro-1-(4-nitrophenyl)-1 H -tetrazole. A comparison of the thermal decomposition mechanisms of these secondary explosives was made by detecting NO 2 molecules released under controlled pyrolysis between 25 and 350 °C. The results show excellent agreement with the thermogravimetric and differential thermal analysis (TGA–DTA) results. A specially designed PA cell made of stainless steel was filled with explosive vapor and pumped using second harmonic, i.e., λ  = 532 nm, pulses of duration 7 ns at a 10 Hz repetition rate, obtained using a Q-switched Nd:YAG laser. The use of a combination of PA and TGA–DTA techniques enables the study of NO 2 generation, and this method can be used to scale the performance of these explosives as rocket fuels. The minimum detection limits of the four explosives were 38 ppmv to 69 ppbv, depending on their respective vapor pressures.

Description: For the first time, spatial distribution of major and trace elements has been studied in cholesterol gallstones using time-of-flight secondary mass ion mass spectrometry (TOF-SIMS). The TOF-SIMS has been used to study the elemental constituents of the center and surface parts of the gallstone sample. We have classified the gallstone sample using Fourier transform spectroscopy. The detected elements in cholesterol gallstone sample were carbon (C), hydrogen (H), calcium (Ca), sodium (Na), potassium (K), strontium (Sr), copper (Cu), iron (Fe), chromium (Cr), mercury (Hg) and lead (Pb). The detected molecules in the cholesterol gallstone were CH 3 + , CO 3 + , CaCO 3 + and C 3 H + . Our results revealed that the contents of these elements in cholesterol gallstone were higher in the center part than that in the surface part. In the present paper, we have also presented the UV–Vis spectroscopic studies of the center and surface parts of the gallstone sample which indicated the presence of a higher content of cholesterol in the surface part and bilirubin in the center part.

Description: Numerical experiments are carried out to calculate continuum emissivity and opacity of plasmas produced from laser-irradiated Au and Pb targets as hohlraum wall materials. Targets are considered to be solid or porous with different initial densities. Simulation results show a good agreement compared with the measured data. The results show that under identical conditions, X-ray emission is higher for Au plasma; however, by decreasing initial densities, X-ray yield enhancement is greater for Pb plasma. By using a Pb target with initial density of about 1.14 g cm −3 instead of solid Au target, the same X-ray yield even more can be obtained. Calculations also show that in the conditions of solid density targets, Pb plasma offers a little lower opacity in soft X-ray region. Decreasing initial density of Pb causes its opacity to increase and get closer to the opacity of solid Au which in turn reduces energy losses in hohlraum wall.

Description: We report the two-photon interference properties of a photon pair generated in a type-II collinear periodically poled KTiOPO 4 (PPKTP) crystal pumped by a 406-nm diode laser capable of producing a single or dual longitudinal mode (LM). When the Hong–Ou–Mandel (HOM) interference signals in the PPKTP crystal pumped by a dual-mode diode laser were investigated at various crystal temperatures, it was found that the maximum visibility of the HOM interference signal depends on the relative strength of the dual LMs of the pump laser. The HOM interference pattern was numerically calculated considering the dual LM components of the pump laser diode and the crystal temperature, and was found to be in good agreement with the experimental results.

Description: One- and two-ring aromatics such as toluene and naphthalene are frequently used molecular tracer species in laser-induced fluorescence (LIF) imaging diagnostics. Quantifying LIF signal intensities requires knowledge of the photo-physical processes that determine the fluorescence quantum yield. Collision-induced and intramolecular energy transfer processes in the excited electronic state closely interact under practical conditions. They can be separated through experiments at variable low pressures. Effective fluorescence lifetimes of gaseous toluene, 1,2,4-trimethylbenzene, anisole, naphthalene, and 1-methylnaphthalene diluted in CO 2 were measured after picosecond laser excitation at 266 nm and time-resolved detection of fluorescence intensities. Measurements in an optically accessible externally heated cell between 296 and 475 K and 0.010–1 bar showed that effective fluorescence lifetimes generally decrease with temperature, while the influence of the bath-gas pressure depends on the respective target species and temperature. The results provide non-radiative and fluorescence rate constants and experimentally validate the effect of photo-induced cooling.

Description: The incorporation of fluorine atoms into the silicon dioxide lattice upon F + ion implantation and the formation of silicon (germanium) nanocrystals in SiO 2 upon Si + (Ge + ) ion implantation have been numerically simulated. The calculations for F have been performed by the density functional theory (DFT) method; the calculations for Si and Ge have been carried out by combining the DFT (in the cluster approximation) and Monte Carlo methods. The energy gain of the fluorine atom attachment to one of silicon atoms with the formation of a nonbridging oxygen hole center (NBOHC) and an energy level appearing in the band gap has been demonstrated. In the case of ion implantation, the simulation at a dissolved Si (Ge) atom concentration of ∼2 at % has revealed the formation of nanocrystals (NCs) with an average size of ∼1 nm.

Description: We present a mid-infrared pulsed cavity ring-down spectroscopy (CRDS) setup based on difference frequency mixing of a tunable dye laser pumped by a Nd:YAG laser and the residual 1064 nm pulse in a temperature-stabilized lithium niobate (LiNbO 3 ) crystal. The performances of such a spectrometer have been investigated by studying the absorption spectrum of methane around 3 µm at room temperature. Our results show a minimum detectable absorption coefficient of 5 × 10 −8  cm −1 . Our approach combines the excellent sensitivity of CRDS with the wide tunable range of difference frequency generation (DFG) with a dye laser. However, the relatively low resolution of this spectrometer prevents the quantification of methane in a wide pressure range. To our knowledge, we report here the first realization and application of a pulsed DFG-based CRDS experiment used for sensitive trace gas detection.

Description: A telescope-grating-deformable scheme is proposed to compensate the angular dispersion of ultrabroadband spectrum. A simple design consideration is formulated based on the large angular dispersion of the idler from noncollinear optical parametric amplification. A proof of principle experiment is demonstrated. A 3-μJ ultrabroadband near-infrared pulse with spectrum range from 700 to 1400 nm has been generated. The technique has great potential to provide an ultrabroadband seed with negligible angular dispersion for high-power amplification of few-cycle pulses.

Description: Up-conversion can be the main mechanism of energy losses in laser glasses with high concentration of erbium ions. This investigation is devoted to the evaluation of up-conversion parameters in several phosphate and silicate Er-doped glasses. Analysis of the luminescent lifetime shortening at high excitation level has shown that the up-conversion parameters in different glasses can differ by an order of magnitude. The smallest up-conversion was observed in Ba crown silicate glass and Li–Ln-phosphate glass.

Description: Wavefront aberrations are one of the largest uncertainty factors in present atom interferometers. We present a detailed numerical and experimental analysis of this effect based on measured aberrations from optical windows. By placing windows into the Raman beam path of our atomic gravimeter, we verify for the first time the induced bias in very good agreement with theory. Our method can be used to reduce the uncertainty in atomic gravimeters by one order of magnitude, resulting in an error of 〈3 × 10 −10 g, and it is suitable in a wide variety of atom interferometers with thermal or ultracold atoms. We discuss the limitations of our method, potential improvements, and its role in future generation experiments.

Description: In this review, we have discussed the potential application of the emerging imaging modality, i.e., optical coherence tomography (OCT) for glucose monitoring in biological tissues. OCT provides monitoring of glucose diffusion in different fibrous tissues like in sclera by determining the permeability rate with acceptable accuracy both in type 1 and in type 2 diabetes. The maximum precision of glucose measurement in Intralipid suspensions, for example, with the OCT technique yields the accuracy up to 4.4 mM for 10 % Intralipid and 2.2 mM for 3 % Intralipid.

Description: Optical-feedback cavity-enhanced absorption spectroscopy is a highly sensitive trace gas sensing technique that relies on feedback from a resonant intracavity field to successively lock the laser to the cavity as the wavelength is scanned across a molecular absorption with a comb of resonant frequencies. V-shaped optical cavities have been favoured in the past in order to avoid additional feedback fields from non-resonant reflections that potentially suppress the locking to the resonant cavity frequency. A model of the laser–cavity coupling demonstrates, however, that the laser can stably lock to a resonant linear cavity, within certain constraints on the relative intensity of the two feedback sources. By mode mismatching the field into the linear cavity, we have shown that it is theoretically and practically possible to spatially filter out the unwanted non-resonant component in order for the resonant field to dominate the feedback competition at the laser. A 5.3  \(\upmu \hbox {m}\)  cw quantum cascade laser scanning across a \(\hbox {CO}_2\) absorption feature demonstrated stable locking to achieve a minimum detectable absorption coefficient of \(2.7\,\times \,10^{-9}\,\hbox {cm}^{-1}\) for 1-s averaging. Detailed investigations of feedback effects on the laser output verified the validity of our theoretical models.

Description: A new method of pump-coupling in diode-pumped alkali vapor amplifier is reported, which uses ring-LD to tightly surround the alkali vapor cell for directly coupled side-pumping. The kinetic and fluid dynamic modeling, numerical approaches of the ring-LD side-pumped configuration are proposed and applied to the static and the flowing-gas Cs vapor amplifiers. Pump intensity and temperature distribution in the cell are simulated. Influences of some important factors on laser power are calculated and analyzed. Comparisons of different pumped configurations are made, demonstrating the highest utilizing efficiency of pump power of the ring-LD side-pumped configuration. Thus the model is very helpful for designing high-power side-pumped alkali vapor amplifiers.

Description: Within the frame of the one-electron approximation, we calculate the electron binding energies of the \(\hbox {Na}_{55}^-\) cluster which allows for the identification of the icosahedral structure of the cluster through comparison with experimental photoelectron spectroscopy data. The surface of the icosahedral cluster is represented as a slightly deformed spherical surface, and the corresponding splitting of the energy levels caused by this symmetry reduction is calculated. Subsequently, we demonstrate that the calculated energies of photoelectrons agree very well with the experimental values. This gives an unambiguous demonstration of the role of the cluster structure in photoelectron spectra, whereas electronic shell filling effects are less important.

Description: Turbulent mixing is highly important in flows that involve heat and mass transfer. Information on turbulent heat flux is needed to validate the mixing models implemented in numerical simulations. The calculation of turbulent heat fluxes requires instantaneous information on temperature and velocity. Even using minimally intrusive laser optical methods, simultaneous measurement of temperature and velocity is still a challenge. In this study, thermographic phosphor particles are used for simultaneous thermometry and velocimetry: conventional particle image velocimetry is combined with temperature-dependent spectral shifts of BAM:Eu 2+ phosphor particles upon UV excitation. The novelty of this approach is the analysis of systematic errors and verification using the well-known properties of a heated turbulent jet issuing into a low velocity, cold coflow. The analysis showed that systematic errors caused by laser fluence, multiple scattering, or preferential signal absorption can be reduced such that reliable measurement of scalar fluxes becomes feasible, which is a prerequisite for applying the method to more complex heat transfer problems.

Description: Multicolor deep-ultraviolet femtosecond pulses are generated in a spectral range of 220–300 nm with pulse energies exceeding 1 μJ. Pulses with shorter wavelengths are also generated with the shortest wavelength of 185 nm. These pulses are generated through cascaded four-wave mixing induced in hydrogen gas by use of three-color femtosecond pump pulses at 1200, 800, and 267 nm. The third pulse dramatically enhances the intensities of the multicolor deep-ultraviolet pulses. The cross-phase modulation induced by the two intense near-infrared pulses broadens the spectral width of each multicolor emission, resulting in a spectral width supporting a transform-limited duration shorter than 10 fs.

Description: The current density in a superlattice exposed to a quantizing electric field and the terahertz field has been calculated. The calculations have been carried out taking into account inelastic scattering of charge carriers by phonons. The possibility of an absolute negative conductivity, i.e., the emergence of electric current opposing the direction of the quantizing electric field, has been demonstrated.

Description: For the first time, zinc oxide epitaxial films on silicon were grown by the method of atomic layer deposition at a temperature T = 250°C. In order to avoid a chemical reaction between silicon and zinc oxide (at the growth temperature, the rate constant of the reaction is of the order of 10 22 ), a high-quality silicon carbide buffer layer with a thickness of ~50 nm was preliminarily synthesized by the chemical substitution of atoms on the silicon surface. The zinc oxide films were grown on n - and p -type Si(100) wafers. The ellipsometric, Raman, electron diffraction, and trace element analyses showed that the ZnO films are epitaxial.

Description: A technique for the evaluation of the electron work function of metallic single crystals and the electron work function anisotropy has been developed in the framework of the electron-statistical method. The surface energy and the electron work function have been calculated for crystal faces of allotropic modifications of 4 d - and 5 d -metals. A change in the electron work function due to the allotropic transformations has been estimated, and the periodic dependence of the electron work function has been determined. It has been shown that the results obtained using the proposed technique correlate with the available experimental data for polycrystals.

Description: It has been experimentally shown that a longitudinal thermal-diffusion autosoliton, which is generated in a nonequilibrium electron–hole plasma in p -InSb, in an external longitudinal magnetic field acquires diamagnetic properties. The results of the calculation and numerical estimates of the diamagnetism have been presented.

Description: Based on the free energy density functional method, the early stage of decomposition of a onedimensional binary alloy corresponding to the approximation of regular solutions has been simulated. In the simulation, Gaussian composition fluctuations caused by the initial alloy state are taken into account. The calculation is performed using the block approach implying discretization of the extensive solution volume into independent fragments for each of which the decomposition process is calculated, and then a joint analysis of the formed second phase segregations is performed. It was possible to trace all stages of solid solution decomposition: nucleation, growth, and coalescence (initial stage). The time dependences of the main phase distribution characteristics are calculated: the average size and concentration of the second phase particles, their size distribution function, and the nucleation rate of the second phase particles (clusters). Cluster trajectories in the size–composition space are constructed for the cases of growth and dissolution.

Description: A dynamic model has been proposed for describing the extrusion of a single layer of a liquid-crystal (LC) material into a meniscus from an N -layer circular free-standing smectic film (FSSF). In the framework of this model, the main mechanism responsible for the process of the thinning (extrusion) of the LC material from the N -layer FSSF is based on the appearance of a spatial pressure gradient directed along the radius of the circular FSSF. This gradient is formed due to the difference in the disjoining pressures on both sides of the front separating the N - and ( N –1)-layer domains of the smectic film. The proposed model allows taking into account the influence of the meniscus on dynamic characteristics, such as the time required for the complete extrusion of a single layer from the N -layer FSSF and the velocity of propagation of the front separating the N - and ( N –1)-layer domains in the process of the thinning of the smectic film formed by molecules of 5- n -alkyl-2-(4- n -(perfluoroalkyl-methyleneoxy))pentyl.

Description: Oxide compounds Pr 2 Sn 2 O 7 and Nd 2 Sn 2 O 7 have been obtained by solid-phase synthesis. The effect of temperature on the heat capacity of Pr 2 Sn 2 O 7 (360–1045 K) and Nd 2 Sn 2 O 7 (360–1030 K) has been studied using differential scanning calorimetry. The thermodynamic properties of the compounds (changes in enthalpy, entropy, and the reduced Gibbs energy) have been calculated by the experimental data of C p = f ( T ).

Description: The phonon spectra in thin layers of bismuth telluride and solid solutions of Bi 2– x Sb x Te 3– y Se y of different composition, belonging to three-dimensional topological insulators, have been investigated by micro-Raman spectroscopy, and the morphology of an interlayer van der Waals (0001) surface in them has been studied by semicontact atomic force microscopy at room temperature. The analysis of the Raman spectra and the intensity ratio of active and inactive longitudinal optical modes depending on the composition, morphology of the interlayer surface, and thickness of the layers enabled the estimation of the effect of topological surface states of Dirac fermions, associated with the strengthening of the electron–phonon interaction as a result of resonance Raman scattering, and the identification of the compositions, in which the contribution of topological surface states becomes dominant.

Description: The irradiation of metallic films by a nanosecond pulsed laser leads to a self-assembly of nanoparticle arrays. This method has been used to prepare bimetallic Au/Co nanoparticles on a SiO 2 substrate. The microstructure and morphology of the bimetallic nanoparticles have been investigated using scanning electron microscopy and transmission electron microscopy. It has been shown that the bimetallic nanoparticles have a hemispherical shape with a single-crystal structure and an average size of ~50 nm. The magnetic properties of these nanoparticles have been examined using a vibrating-sample magnetometer in the transverse and longitudinal directions. It has been found that the direction of the magnetization of the bimetallic nanoparticles lies in the plane of the substrate, and the coercive forces in the transverse and longitudinal directions differ by 25%. The use of the vibrating-sample magnetometer method makes it possible to investigate the differences in the magnetic saturations and the coercive forces of an array of bimetallic nanoparticles on a large surface area. The performed investigations have demonstrated that the anisotropic nanomagnetic materials with the desired magnetic orientation can be easily and quickly prepared by means of thermal laser treatment.

Description: Thin films of partially deuterated betaine phosphate have been grown by the evaporation on Al 2 O 3 (110) and NdGaO 3 (001) substrates with a preliminarily deposited structure of interdigitated electrodes. The grown films have a polycrystalline block structure with characteristic dimensions of blocks of the order of 0.1–1.5 mm. The degree of deuteration of the films D varies in the range of 20–50%. It has been found that, at the antiferroelectric phase transition temperature T c afe = 100–114 K, the fabricated structures exhibit an anomaly of the electrical capacitance C , which is not accompanied by a change in the dielectric loss tangent tanδ. The strong-signal dielectric response is characterized by the appearance of a ferroelectric nonlinearity at temperatures T 〉 T c afe , which is transformed into an antiferroelectric nonlinearity at T 〈 T c afe . With a further decrease in the temperature, double dielectric hysteresis loops appear in the antiferroelectric phase. The dielectric properties of the films have been described within the framework of the Landau-type thermodynamic model taking into account the biquadratic coupling ξ P 2 η 2 between the polar order parameter P and the nonpolar order parameter η with a positive coefficient ξ. The E–T phase diagram has been constructed.

Description: In this work, we present a modification to conventional X-rays fluorescence using electrons as excitation source and compare it with the traditional X-ray excitation for the study of pigments. For this purpose, we have constructed a laser-based source capable to produce X-rays as well as electrons. Because of the large penetration depth of X-rays, the collected fluorescence signal is a combination of several material layers of the artwork under study. However, electrons are stopped in the first layers, allowing a more superficial analysis. We show that the combination of both excitation sources can provide extremely valuable information about the structure of the artwork.

Description: A correction for the undesirable effects of direct and indirect cross-interference from water vapour on ammonia (NH 3 ) measurements was developed using an optical laser sensor based on cavity ring-down spectroscopy. This correction relied on new measurements of the collisional broadening due to water vapour of two NH 3 spectral lines in the near infra-red (6548.6 and 6548.8 cm −1 ), and on the development of novel stable primary standard gas mixtures (PSMs) of ammonia prepared by gravimetry in passivated gas cylinders at 100 μmol mol −1 . The PSMs were diluted dynamically to provide calibration mixtures of dry and humidified ammonia atmospheres of known composition in the nmol mol −1 range and were employed as part of establishing a metrological traceability chain to improve the reliability and accuracy of ambient ammonia measurements. The successful implementation of this correction will allow the extension of this rapid on-line spectroscopic technique to exposure chamber validation tests under controlled conditions and ambient monitoring in the field.

Description: In this paper, we analyze the influence of large-scale segmentation errors in the morphology of high-performance optical gratings. It is thus assumed that the optical grating under consideration (typical lateral extends S are 10–1000 mm) can be spatially decomposed into a great many but unique sub-segments ( \(\ll S\) ; typical extends are 10–100  \(\upmu \mathrm{m}\) ). Any violation of the perfect periodicity will result in the generation of stray light, especially Rowland ghosts, which radiate into a small angular region around the grating’s diffraction orders. In this paper, we focus on three different kinds of segmentation errors. On the one hand, there are statistic as well as deterministic alignment errors between otherwise perfect sub-segments. On the other hand, we analyze the effect of chirping of geometrical parameters, i.e., the groove width, within every sub-segment. Most importantly, we find that the particular type of imperfection results in a unique characteristic of the according stray light spectrum which thus acts as a fingerprint. We come to this conclusion on three different ways. First, we rely on a simple theoretical model that is based on scalar diffraction theory. Second, we have performed rigorous numerical simulations for a high aspect ratio purely dielectric spectrometer grating ( \(\hbox {period} = {667}\,\mathrm{nm}\) ). Third, the very same grating was then fabricated by e-beam lithography and its stray light spectrum was measured with a purposely designed optical setup. Eventually, all different routes to analyze the problem turn out to be in very good agreement, and we are confident that stray light measurements can be used as an important tool in the detection of fabrication imperfections.

Description: We report diffusion coefficients of optically pumped lithium atoms in helium buffer gas. The free-induction decay and the spin-echo signals of ground-state atoms were optically detected in an external magnetic field with the addition of field gradient. Lithium hot vapor was produced in a borosilicate-glass cell at a temperature between 290 and \(360\,^{\circ }\hbox {C}\) . The simple setup using the glass cells enabled lithium atomic spectroscopy in a similar way to other alkali-metal atoms and study of the collisional properties of lithium atoms in a hot-vapor phase.

Description: We propose and demonstrate a laser frequency stabilization scheme which generates a dispersion-like tunable Doppler-free dichroic lock (TDFDL) signal. This signal offers a wide tuning range for lock point (i.e. zero-crossing) without compromising on the slope of the locking signal. The method involves measurement of magnetically induced dichroism in an atomic vapour for a weak probe laser beam in the presence of a counter-propagating strong pump laser beam. A simple model is presented to explain the basic principles of this method to generate the TDFDL signal. The spectral shift in the locking signal is achieved by tuning the frequency of the pump beam. The TDFDL signal is shown to be useful for locking the frequency of a cooling laser used for magneto-optical trap (MOT) for 87 Rb atoms.

Description: Detection of multiple transitions in NO and H 2 O using multi-mode absorption spectroscopy, MUMAS, with a quantum cascade laser, QCL, operating at 5.3 μm at scan rates up to 10 kHz is reported. The linewidth of longitudinal modes of the QCL is derived from pressure-dependent fits to experimental MUMAS data. Variations in the spectral structure of the broadband, multi-mode, output of the commercially available QCL employed are analysed to provide accurate fits of modelled MUMAS signatures to the experimental data.

Description: We propose a novel approach to site-resolved detection of a 2D gas of ultracold atoms in an optical lattice. A near-resonant laser beam is coherently scattered by the atomic array, and after passing a lens its interference pattern is holographically recorded by superimposing it with a reference laser beam on a CCD chip. Fourier transformation of the recorded intensity pattern reconstructs the atomic distribution in the lattice with single-site resolution. The holographic detection method requires only about two hundred scattered photons per atom in order to achieve a high reconstruction fidelity of 99.9 %. Therefore, additional cooling during detection might not be necessary even for light atomic elements such as lithium. Furthermore, first investigations suggest that small aberrations of the lens can be post-corrected in imaging processing.

Description: We experimentally demonstrate that the spectral resolution of Fourier transform interferometer could be greatly enhanced by using the dispersive property of semiconductor GaAs in the near infrared region and obtain the frequency distribution of the input light from interference pattern by defining a new frequency transform factor. The results show the effectiveness of this method in the slow light interference system.

Description: Characteristics of a ZnSe:Fe 2+ laser operating at room temperature of active polycrystalline elements with large transversal dimensions are investigated. The active elements had a shape of plates with diameters D  = 25–63 mm and width of ~4 mm, doped from two sides with iron ions by the diffusion method. The plates were doped in the process of hot isostatic pressing at an argon pressure of 100 MPa and temperature of 1250 °C for 75–151 h. The laser was pumped by a non-chain electrodischarge HF laser operated in a single-pulse mode. The employment of active elements with greater transversal dimensions resulted in a suppressed transversal parasitic oscillation at large diameters of the pumping spot. The generation energy of 1.43 J with the slope efficiency η slope  = 53 % and the total efficiency with respect to the energy absorbed in an active element η abs  ≈ 48 % was obtained on the sample of diameter D  = 63 mm.

Description: The hole transport buffer layer (HTL) known as PEDOT:PSS is found to be sensitive to polar solvents often used in the preparation of solution-processed perovskite-based solar cell. We employed \(\hbox {CH}_{3}\,\hbox {NH}_{3}\,\hbox {PbI}_{3}\) perovskite absorber sandwiched between two charge transport layers to analyze the effect of precursor solvent. By introducing skin-depth interfacial defect layer (IDL) on PEDOT:PSS film we studied the overall performance of the devices using one-dimensional device simulator. Both enhanced conductivity and variations in valence band offset (VBO) of IDL were considered to analyze device performance. A power conversion efficiency (PCE) of the devices was found to grow by 35 % due to increased conductivity of IDL by a factor of 1000. Furthermore, we noted a drastic reduction in PCE of the device by reducing the work function of IDL by more than 0.3eV . The thickness of interfacial defect layer was also analyzed and found to decrease the PCE of the devices by 18 % for fourfold increase in IDL thickness. The analysis was remarkably reproduced the experimentally generated device parameters and will help to understand the underlying physical process in perovskite-based solar cell.

Description: We present a diode laser system optimized for laser cooling and atom interferometry with ultra-cold rubidium atoms aboard sounding rockets as an important milestone toward space-borne quantum sensors. Design, assembly and qualification of the system, combing micro-integrated distributed feedback (DFB) diode laser modules and free space optical bench technology, is presented in the context of the MAIUS (Matter-wave Interferometry in Microgravity) mission. This laser system, with a volume of 21 l and total mass of 27 kg, passed all qualification tests for operation on sounding rockets and is currently used in the integrated MAIUS flight system producing Bose–Einstein condensates and performing atom interferometry based on Bragg diffraction. The MAIUS payload is being prepared for launch in fall 2016. We further report on a reference laser system, comprising a rubidium stabilized DFB laser, which was operated successfully on the TEXUS 51 mission in April 2015. The system demonstrated a high level of technological maturity by remaining frequency stabilized throughout the mission including the rocket’s boost phase.

Description: We demonstrate fourfold coherent combining in a gas-filled hollow-fiber compressor with 92 % efficiency. Our passive approach relies on the use of carefully oriented birefringent plates for temporal pulse dividing and combining. We perform a detailed theoretical and experimental analysis of the effects degrading the combining process, as polarization change or nonlinear interactions between pulse replicas. We show how to overcome these limitations to generate 10-fs output pulses with high temporal quality.

Description: The magnetic state of a system of particles with a “large” spin of 3/2 in the presence of isotropic exchange interaction in the system has been studied on the basis of a derived spin Hamiltonian. It has been shown that, at a positive contribution of the exchange interaction, an unstable nematic state appears and transforms to a stable ferromagnetic state (with an average spin of 3/2). The excitation spectrum in the ferromagnetic state is a triply degenerate Goldstone-type gapless magnon mode. At a negative sign of the exchange contribution, an antinematic state is stable with respect to a transition to a ferromagnetic state, which is forbidden. In this case, the antinematic always occurs in the state of a phase transition to an unstable antiferromagnetic state, the excitation spectrum of which is characterized by a single nondegenerate Goldstone mode.