Efficiency of the structure analysis of complex molecules in the gas phase by their optical rotation

It was shown in the dipole approximation of optical rotation that in the general case only in orientationally anisotropic vapors is the rotational force dependent on the intramolecular orientation of both the electric and magnetic dipole moments. Expressions relating the optical rotational force to the intramolecular orientation of these moments, the orientational distribution in an anisotropic ensemble, and the configuration of a measurement have been obtained. Calculated dependences of the rotational force on the intramolecular orientation of the magnetic moment at a fixed electric moment and “rotational force excitation spectra” obtained for different types of rigid asymmetric top molecules and rotational contours are presented. It is proposed to measure the intramolecular orientation of the electric and magnetic dipole moments with the use of the rotational force normalized to that detected in the case of observation at a “magic” angle to the direction of the exciting light electric vector. Institute of Molecular and Atomic Physics of the Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 843–849, November–December, 1998.     

Orientation of liquid-crystal molecules on substrates exposed to argon-ion bombardment

The possibility for homogeneous orientation of liquid-crystal (LC) molecules was studied after argon-ion bombardment of substrates (Si, Ge) transparent in the infrared (IR) spectral region. The orientation of the LC molecules was monitored by IR spectroscopy. Nematic LC 4-methoxybenzylidene-4′-butylaniline (MBBA) was used to study the molecular orientation. Absorption spectra were analyzed near the band with maximum at 1630 cm⁻¹ corresponding to − CH=N-group vibrations along the long axis of the MBBA molecule. The type and degree of initial orientation of the LC molecules were determined from the correlation of the integrated absorptions of this band without and with an applied electric field (above the threshold voltage for the Fredericksz effect). It has been established that an increased ion fluence results in a planar orientation of the LC molecules and in a gradual transformation of the planar orientation of the molecules to a homeotropic one with preliminary argon-ion bombardment of substrates at energies of 250 eV and 1.25 keV, respectively. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 763–767, November–December, 2008.     

Peculiarities of linear scaling of cylindrical glass active elements of solid-state lasers

Optimization of the glass cylindrical active element (AE) of a solid-state laser is carried out. Dependences of the optical quality of a laser medium on scale-geometry parameters of the AE with different-intensity optical pumping are obtained. The possibility of considerable increasing of the laser efficiency by using an aperture diaphragm is shown. Baltic State Technical University, 1, 1st. Krasnoarmeiskaya St., St.-Petersburg, 198005, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 734–737, November–December, 1997.     

Thermally stimulated transformation of the structure of cobalt complexes in polyvinyl alcohol-cobalt(II) chloride systems

We present the kinetic and temperature dependences of the optical absorption of thermochromic films of polyvinyl alcohol with added CoCl₂. Based on the data obtained, we have analyzed the possibility that tetrahedral cobalt complexes are formed from octahedral complexes. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 826–829, November–December, 2007.     

Structural, optical and electrical properties of cubic AlN films deposited by laser molecular beam epitaxy

Cubic AlN films were successfully deposited on TiN buffered Si (100) substrates by a laser molecular beam epitaxy (LMBE) technique, and their crystal structure and optical and electrical properties were studied. The results indicate that cubic AlN films show the NaCl-type structure with a (200) preferred orientation, and the lattice parameter is determined to be 0.4027 nm. The Fourier transform infrared (FTIR) pattern of the cubic AlN film displays sharp absorption peaks at 668 cm⁻¹ and 951 cm⁻¹, corresponding to the transverse and longitudinal optical vibration modes. Ellipsometric measurements evidence a refractive index of 1.66–1.71 and an extinction coefficient of about zero for the cubic AlN film in the visible range. Capacitance–voltage (C–V) traces of the metal–insulator–semiconductor (MIS) device exhibit that the cubic AlN film has a dielectric constant of 8.1, and hysteresis in the C–V traces indicates a significant number of charge traps in the film.     

Growth and structure of epitaxial diamond films grown on Si(111) single crystals

Experiments on growing single-crystal diamond films on silicon crystals with (111) surface orientation have been performed. Results attesting to the possibility of obtaining thin heteroepitaxial films are presented. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 5, 414–418 (10 March 1997)     

Wave front transformation of optical vortices with multiwave interactions in resonant media

The transformation of singular light beams is analyzed theoretically for multiwave interactions on amplitude and phase dynamic holograms in media with a resonant nonlinearity. The possibility of multiplying topological charge using different diffraction orders is demonstrated and optimal conditions for parametric energy exchange are determined which ensure retention of the structure of the wave front of optical vortices. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 395–402, May–June, 2009.     

Polarization of Luminescence in the Nanostructure Si/CaF<Subscript>2</Subscript> Upon Polarization of the Nuclear Spins of Fluorine

The laws governing polarization of luminescence in the nanostructure Si/CaF₂ upon polarization of the spins of the fluorine nuclei by means of optical excitation of charge carriers are considered theoretically. The possibility of studying experimentally the properties of nuclear spins in analyzing luminescence is shown. The polarization of luminescence is most informative in the range of excitation rates of charge carriers from 3⋅10⁷ to 3⋅ 10⁸ sec⁻¹ with the CaF₂ layer of thickness from 0.6 to 0.8 nm and optical excitation polarization degree of 0.1. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 524–529, July–August, 2005.     

Resonant-Optical Detection of Nuclear Magnetization in the Si/CaF<Subscript>2</Subscript> Nanostructure

We have considered theoretically the characteristic features of optical detection of nuclear magnetization in the Si/CaF₂ structure under the conditions of EPR and NMR by measuring luminescence polarization. We show that application of EPR makes it possible to detect weak nuclear fields, but the time of spin relaxation of electrons imposes its constraint. The application of NMR is limited by nuclear fields of no less than 15–20 Gs. The possibility of using optical NMR for direct measurement of the nuclear field from changes in the luminescence polarization spectrum is shown. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 644–649, September–October, 2005.     

Fine structure of excitonic levels in quantum dots

The experimental results of a study of the fine structure of the levels of excitons localized in InAlAs quantum dots in an AlGaAs matrix are reported. Transformations from optical orientation to alignment and from alignment to orientation, which occur due to the exchange splitting of a dipole-active excitonic doublet and are allowed by the low symmetry of a quantum dot, are observed in a longitudinal magnetic field (Faraday geometry). A comparison of theory with experiment for a self-organized ensemble of quantum dots enables a determination of the character of the distribution over the dipole orientations for resonance optical transitions. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 10, 766–771 (25 May 1997)     

Optical control of the anisotropy of the orientation of molecules in a liquid

The control of the anisotropy of the orientation of molecules in pure 1,2-dichlorobenzene, C₆H₄Cl₂ at room temperature is demonstrated experimentally. To accomplish the optical control, the medium is exposed to non-resonant excitation with two successive linearly polarized laser pulses with a duration of 60 fs. The state of transient anisotropy is probed with the third pulse by detecting the ultrafast optical Kerr effect via optical heterodyne detection and synchronous demodulation. It is shown that variations in the two parameters, the delay time between two pump pulses, and the angle between the polarization directions of the pump pulses ensure the control of the anisotropy of the orientation of molecules in the subpicosecond region. Original Russian Text ? V.G. Nikiforov, G.M. Safiullin, A.G. Shmelev, A.V. Leont’ev, V.S. Lobkov, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 10, pp. 757–761.     

Production of SiO2 films from alkoxides and their optical properties

The specific features of spectrochemical properties of active silica-gel films in air media with various pH have been studied. SiO₂ films were obtained by acid hydrolysis of tetraethoxysilane. The optical properties were controlled by immobilization of indicators (bromocresol purple, phenol red). The possibility of using them as optical-fiber sensors is shown. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 503–506, July–August, 2000.     

Collinear interaction of bichromatic radiation with one acoustic wave in biaxial crystals

The regime of collinear interaction of bichromatic optical radiation in biaxial crystals is considered. It is shown that the possibility of the realization of such an interaction is due to dispersion of the optical axes in a biaxial crystal. Zh. Tekh. Fiz. 69, 131–132 (January 1999)     

Problems of technological use of coherent Bremsstrahlung beams

To determine the possibility of technological use of coherent Bremsstrahlung beams the photonuclear transmutation doping of silicon by aluminum upon γ-quantum irradiation from the aligned single-crystal target was studied. An increase in aluminum concentration by approximately ten times was obtained upon γ-radiation of silicon from the crystalline target aligned by the crystallographic axis 〈111〉 along the direction of the electron beam with the energy of 1200 MeV. The orientation effect of an increase in the yield of γ-radiation from silicon and tungsten crystals in the range of energies of accelerated electrons of 300–1200 MeV was examined. This result is essential for the estimation of a possible minimum energy of electrons at which the use of the orientation effect is reasonable.     

Films made of substituted azobenzene polycomplexes with cobalt for polarization holography

We have studied the possibility of recording holograms in films of the 4-methacroyloxy-(4′-carboxy-3′-hydroxy)-2-chloroazobenzene polycomplex with cobalt, with parallel and orthogonal orientation of the light beam polarization. We have shown that these films can be used as recording media for polarization holography. The characteristic features of relaxation of the diffraction efficiency of the holograms are connected with cistrans isomerization of the azobenzene groups and the characteristic features of structural rearrangement in the polymer matrix. We hypothesize that the information-related characteristics of the studied recording media can be controlled by external electric or magnetic fields, due to the presence of magnetic metal ions within the polymer film. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 830–832, November–December, 2007.     

Thermal lensing study and athermal directions in flashlamp-pumped Nd:KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> laser crystal

Thermal lensing has been studied by a probe beam technique in flashlamp-pumped Nd:KGdW laser rods with rod axes positioned in the N _p–N _g plane and making different angles with the N _g optical indicatrix axis. It was found that the orientation of principal meridional planes of the astigmatic thermal lens in Nd:KGdW corresponds to the directions with maximum and minimum values of thermal-expansion coefficient in the plane perpendicular to the rod axis. The athermal Nd:KGdW laser crystal orientation defined as orientation with weak positive near spherical thermal lens has been determined to make an angle of 30^○–40^○ with the N _g axis for light polarization E∥N _m.     

Synthesis and characterisation of polypyrrole–indium phosphide composite film

Polypyrrole (PPy)–indium phosphide (InP) composite material was electrochemically prepared by the incorporation of InP into a PPy matrix during electrochemical synthesis (cycling) under magnetic stirring from the acetonitrile/LiClO4 electrolyte containing the Py and InP particles. The PPy–InP composite material was designed to explore new approaches to improve light-collection efficiency in polymer photovoltaic. The samples were characterised by cyclic voltammetry, impedance spectroscopy measurement, scanning electron microscopy, energy dispersive X-ray spectroscopy, UV–visible and photoelectrochemical measurements. It was observed that the photocurrent of the composites was higher than that of the single PPy films and increased with InP concentration. The study showed that the presence of InP particles in the polymeric film improves the optical and the photovoltaic properties of PPy and give information on the use possibility of these films for photovoltaic cells' application.     

Pulsed holmium laser ablation of tissue phantoms: correlation between bubble formation and acoustic transients

5 Pa served as tissue phantoms to evaluate such effects. Holmium laser pulses (wavelength: 2.12 μm, duration: 180 μs FWHM), were delivered through 400 and 600 μm diameter optical fibers inserted into cubes of clear gel. Bubble effects were investigated using simultaneous flash micro-videography and pressure recording for radiant exposures of 20–382 J/cm². Bubble formation and bubble collapse induced pressure transients were observed regardless of phantom stiffness. Bubbles of up to 4.2 mm in length were observed in gels with a Young’s modulus of 2.9×10⁵ Pa at a pulse energy of 650 mJ. An increase of Young’s modulus (reduction in water content) led to a monotonic reduction of bubble size. In the softest gels, bubble dimensions exceeded those observed in water. Pressure amplitudes at 3 mm decreased from 100±14 bars to 17±6 bars with increasing Young’s modulus over the studied range. Theoretical analysis suggested a major influence on bubble dynamics of the mass and energy transfer through the bubble boundary. Received: 26 August 1996/Revised version: 10 February 1997     

Characterization of probe lasers for thin-film optical measurements

The peak-power-density stability and beam-wander precision of a probe laser are important factors affecting the inspection results in precise thin-film optical measurements. These factors are also key to evaluating a probe laser for in-line long-time operation of precise thin-film optical measurements. The peak-power density and beam wander of liner helium–neon (He–Ne) lasers, random He–Ne lasers, and diode lasers as functions of time are investigated experimentally using a beam profiler. It is found that the linear polarized He–Ne laser is considered to be a promising candidate for a probe laser employed in precise thin-film optical measurements due to better peak-power-density stability and beam-wander precision. Both the peak-power-density stability and beam-wander precision of He–Ne lasers are usually better than that of diode lasers, but an adequate warm-up of He–Ne laser for 30 min is required before thin-film optical measurements are made. After 12 h operation, the linear polarized He–Ne laser is suitable for precise thin-film optical measurements because both the peak-power-density stability and the beam-wander precision reach the minimum level. A cost-effective system composed of two linear polarized He–Ne lasers for long-term operation is proposed. This system can operate for around 0.5–1.2 years in precise thin-film optical measurements under the normal operating life of a He–Ne laser by switching the probe laser every 18 h.     

Negative-index metamaterials: second-harmonic generation, Manley–Rowe relations and parametric amplification

Second harmonic generation and optical parametric amplification in negative-index metamaterials (NIMs) are studied. The opposite directions of the wave vector and the Poynting vector in NIMs results in a “backward” phase-matching condition, causing significant changes in the Manley–Rowe relations and spatial distributions of the coupled field intensities. It is shown that absorption in NIMs can be compensated by backward optical parametric amplification. The possibility of distributed-feedback parametric oscillation with no cavity has been demonstrated. The feasibility of the generation of entangled pairs of left- and right-handed counter-propagating photons is discussed. PACS 78.67.-n; 42.65.Ky; 42.65.Lm