Optics and Spectroscopy (v.104, #6)

The calculation of the energy of the ground state of atoms is the criterion for the correctness of compact analytical atomic wave functions. However, such a test is in fact static. We studied the degree of taking into account electron correlations in various simple analytical wave functions in the dynamic process of reemission by the helium atom of ultrashort pulses of an electromagnetic field. Direct guidelines are given on the use of particular analytical wave functions, which can be helpful in simple calculations and estimations of dynamic processes.
Keywords: 03.65.-w; 34.10.+x; 31.25.Eb; 34.50.Fa

The excitation of transitions from low-lying levels of the tungsten atom by a beam of slow electrons with an energy of 50 eV is studied. The results obtained are used to calculate the total excitation cross sections of the WI energy levels taking into account the branching ratios.
Keywords: 34.50.Fa

Ab initio study of rovibronic energies of the CH 2 + molecular ion by V. G. Solomonik; A. Yu. Yachmenev (818-824).
The potential energy surfaces of the lowest electronic states $$ ilde X $$ 2 A 1 and $$ ilde A $$ 2 B 1 of the CH 2 + molecular ion are calculated in the second order of the perturbation theory with the reference function obtained by the multiconfiguration self-consistent-field method in the complete-active-space approximation. Based on the ab initio calculated potential energy surfaces, the rovibronic energies of CH 2 + are calculated by the variational method using the RENNER Hamiltonian. It is found that the accuracy of the perturbation theory method involving many reference configurations is as good as the accuracy of the best ab initio calculations performed by the configuration interaction method with many reference configurations and by the coupled cluster method with a single reference configuration. Empirical refinement of the two parameters of the potential function leads to good agreement between calculation and experiment, except for the wavenumbers of the $$ ilde A $$ (0, 3, 0)1 ← $$ ilde X $$ (0, 0, 0)0 transitions.
Keywords: 31.15.Md; 31.50.-x; 33.20.Vq

A procedure for calculating the higher-order contributions of the perturbation theory to the interruption function S(b) is considered, and the final expressions for the third-order terms are derived. It is shown that, in the general case, the new resonance functions for the higher orders of the interruption function can be obtained by the Fourier transform of the coefficients of the intermolecular interaction potential.
Keywords: 33.70.Jg

The properties of emission, absorption, and dual fluorescence excitation of 3-hydroxyflavone in acetonitrile are studied under the conditions of dynamic quenching by potassium iodide with concentrations up to 4 × 10−2 M. The normal and tautomeric forms undergo quenching, which is more efficient for the tautomeric form. An interesting circumstance is that the absorption in the S 0S 1 and S 0S 2 singlet bands of the solution increases with increasing quencher concentration in the whole region of concentrations used, the steepest rise being recorded in the concentration region from 0 to 5 × 10−3 M. The intensities and quantum yields of the two fluorescence bands show rather complicated nonlinear dependences on the quencher concentration. The long-wavelength fluorescence band, which belongs to the tautomeric form of 3-hydroxyflavone, is quenched considerably stronger. The experimental results reveal the kinetic character of the excited-state proton transfer in molecules of 3-hydroxyflavone in acetonitrile.
Keywords: 33.50.Dq

The properties of the dual fluorescence of 3-hydroxyflavone in acetonitrile are studied under conditions of dynamic quenching by the spin quencher TEMPO in the temperature range from 20 to 80°C. 3-Hydroxyflavone is characterized by the intramolecular excited state proton transfer and its spectrum consists of two well-spaced fluorescence bands belonging to the normal and tautomeric forms. The fluorescence was selectively excited at wavelengths of 290, 304, and 340 nm, belonging to different absorption bands of the luminophore. The character and degree of the temperature quenching of the fluorescence depend on the excitation wavelength and are considerably different for normal and tautomeric fluorescence bands. The Stern-Volmer constants for both forms, calculated from the experimental data on the assumption of the diffusion mechanism of quenching of the excited states, increase with temperature. Both in the pure solutions and in the solutions with the quencher, the intensity ratio of the fluorescence of the initial form and the product increases with heating in the entire temperature range from 20 to 80°C for all the above excitation wavelengths.
Keywords: 33.50.Dq

The IR spectra of the real n(ν) and imaginary κ(ν) parts of the complex refractive index of an industrial high-pressure polyethylene film are measured by the methods of transmission and attenuated total reflectance spectroscopy in the range 700–750 cm−1 taking into account the anisotropy and the structural inhomogeneity of the film over its thickness. It is proposed to use these spectra as the reference spectra for polyethylene films in the range around 720 cm−1.
Keywords: 78.30.Jw

Intramolecular energy transfer in mesogenic europium (III) adduct by D. V. Lapaev; V. G. Nikiforov; A. A. Knyazev; V. I. Dzhabarov; V. S. Lobkov; K. M. Salikhov; Yu. G. Galyametdinov (851-857).
The absorption and emission spectra of a liquid-crystalline melt prepared on the basis of a synthesized mesogenic europium (III) adduct are studied in the temperature range from 77 to 348 K. The main channels and rate constants of intramolecular energy transfer from ligands to Eu (III) ions are determined from the absorption and luminescence spectra and luminescence kinetics of the sample under study. It is shown that the liquid-crystalline melt of the europium (III) adduct has a high photostability and an intense luminescence in the temperature range from 77 to 300 K, which allows one to consider it as a promising material for optoelectronic devices. Above room temperature, the relaxation time of the 5 D 0 level of Eu (III) ions sharply shortens. An analysis of the kinetics of the luminescence corresponding to the 5 D 07 F 2 transition shows that the relaxation of the 5 D 0 level in the temperature range from 300 to 348 K occurs through a charge-transfer state.
Keywords: 33.50.-j

The formation of quasi-metallic defects on the basis of the F L center (F center with a metal atom) has been investigated with the aim of increasing the efficiency and decreasing the pump threshold of laser elements based on alkali-halide crystals. The regularity of formation of quasi-metallic defects in a number of alkali-halide crystals has been established.
Keywords: 78.40.Fy; 78.40.Ha

Optical spectra of (CdF2)0.9(InF3)0.1 semiconductor solid solutions by S. A. Kazanskiĭ; S. A. Klimin; A. S. Shcheulin; M. V. Narozhnyĭ; A. I. Ryskin (861-865).
The differences in the optical spectra of CdF2:In semiconductors with bistable DX centers (concentrated (CdF2)0.9(InF3)0.1 solid solutions) and “standard” samples with a lower impurity concentration used to record holograms are discussed. In contrast to the standard samples, in which complete decay of two-electron DX states and transfer of electrons to shallow donor levels may occur at low temperatures, long-term irradiation of a (CdF2)0.9(InF3)0.1 solid solution by UV or visible light leads to decay of no more than 20% deep centers. The experimental data and estimates of the statistical distribution of electrons over energy levels in this crystal give the total electron concentration, neutral donor concentration, and concentration of deep two-electron centers to be ∼5 × 1018 cm−3, ∼9 × 1017 cm−3, and more than 1 × 1020 cm−3, respectively. These estimates show that the majority of impurity ions are located in clusters and can form only deep two-electron states in CdF2 crystals with a high indium content. In this case, In3+ ions in a limited concentration (In3+ (∼9 × 1017 cm−3) are statistically distributed in the “unperturbed” CdF2 lattice and, as in low-concentrated samples, form DX centers, which possess both shallow hydrogen-like and deep two-electron states.
Keywords: 78.40.-q

Fluctuations of local optical anisotropy of island films by T. A. Vartanyan; N. B. Leonov; A. E. Logunov; A. V. Papko; S. G. Przhibel’skiĭ; V. V. Khromov (866-869).
A method for the determination of the island film structure parameters by measuring fluctuations of optical characteristics of small areas of the film is proposed and implemented. The extinction fluctuations of the laser beam are measured experimentally in a focal spot, in which the polarization of radiation is modulated in time and which is movable over the film. From the optical data thus obtained, the optical absorption anisotropy of the nanometer-size islands of the film is evaluated. It is shown that this characteristic has a considerable frequency dispersion in the region of plasmon resonances of the nanoparticles.
Keywords: 42.25.Bs; 78.20.-e

Refractometry of mechanically compressed (NH4)2SO4 crystals by V. I. Stadnyk; N. A. Romanyuk; M. R. Tuzyak; R. S. Brezvin; I. M. Matviishin; V. M. Gaba (870-874).
The effect of uniaxial mechanical pressure σ m ≤ 150 bar on the spectral (300–800 nm) dependence of the birefringerence Δn i and refractive indices n i of (NH4)2SO4 crystals has been investigated. It is shown that the dispersion of n i (λ) and Δn i (λ) is normal and sharply increases with approach to the absorption edge. It is established that uniaxial pressure does not change the character of the dispersions dn i / and dΔn i / and only affects their magnitudes. It is shown that the increase in the refractive indices under uniaxial stress is mainly due to the increase in the refraction caused by the increase in the band gap and long-wavelength shift of the UV absorption band maximum.
Keywords: 78.20.Fm

Spectral and kinetic properties of an immunoactive 8-azasteroid and a product of its photochemical transformation in aqueous solutions by V. L. Dubovskiĭ; O. V. Gulyakevich; A. L. Mikhal’chuk; T. F. Raĭchenok; S. A. Tikhomirov; G. B. Tolstorozhev (875-885).
The spectral and kinetic properties of an immunoactive 8-azasteroid and a product of its photochemical transformation are studied by the methods of steady-state and transient spectroscopy. It is found that the spectral features of the studied compounds in solvents of different nature are determined by a high sensitivity of the electronic structure of the aminovinyldicarbonyl fragment to intermolecular interactions of the donor-acceptor type. This leads to the existence in solutions of several mesomeric-tautomeric forms that are in a dynamic equilibrium controlled by the experimental conditions. Based on the analysis of the dynamics of the transient spectra of induced absorption and of the spectral and luminescent properties of the extracted photoproduct, the conclusion is made on the direction of the photochemical transformation of 2,3-dimethoxy-8-azagona-1,3,5(10),13-tetraene-12,17-dione and the final product is identified as 6,7-dehydroderivative of the parent compound.
Keywords: 33.50.Dq

Manifestation of gyrotropy upon light scattering in paratellurite by E. Yu. Vorontsova; R. M. Grechishkin; I. A. Kaplunov; A. I. Kolesnikov; V. Ya. Molchanov; I. V. Talyzin; S. A. Tret’yakov (886-889).
Upon scattering of laser radiation at different wavelengths, three optical effects—rotation of the plane of polarization of linearly polarized light, dependence of the specific rotation on the radiation wavelength, and the dependence of the scattered light intensity on the angle between the scattered and incident beams—are simultaneously observed. The intensity distributions of the scattered laser light at 0.488, 0.531 nm, and 0.633 μm along the optical axis of a thick sample of a TeO2 single crystal are visualized. Based on the patterns obtained, the values of the specific rotation are calculated, and the curve of the optical rotation for the visible range is obtained.
Keywords: 78.20.Ek

The light reflection spectra and the magnetorefractive effect in the cobalt-based amorphous ribbons in the IR spectral region (λ = 2.5–25 μm) are studied. These amorphous alloys are characterized by the magnetoimpedance effect, which is enhanced after thermal and laser annealing. It is found that the magnetoimpedance and magnetorefractive effects correlate with each other. The magnetorefractive effect reveals a feature at λ = 15–20 μm and the change of sign in the wavelength region 20–25 μm. It is shown that, in the first approximation, the optical properties of the amorphous alloys in the IR spectral region can be explained on the basis of a modified Hagen-Rubens relation. It is found that the change in the reflection coefficient of amorphous metal films in the IR spectral region under action of a magnetic field is caused by the change in both their magnetic permeability and conductivity, which is caused by the degree of polarization of localized electronic states at the Fermi level.
Keywords: 78.20.Ls; 78.30.-j; 75.50.Kj

Optical characteristics of a system consisting of a photonic crystal with a defect layer of a dense resonant medium described by the modified Bloch equation are considered. Transmission spectra are calculated and regions of existence of bistable optical response of the system are found. It is shown that the effect of internal reflection demonstrated by the dense resonant medium results in variation of reflection and transmission spectra of the photonic crystal and the loop width of the bistable response of the dense resonant medium is determined by the structure of the photonic crystal.
Keywords: 42.65.Pc

Nonlinear interaction of a circularly polarized electromagnetic wave with a dense laser plasma by A. A. Andreev; K. Yu. Platonov; I. V. Rozhanskiĭ (901-908).
The interaction of an intense circularly polarized laser pulse with a layer of plasma of supercritical density is studied. The nonlinear skin effect for the electromagnetic field and the coefficient of collisionless absorption of the laser pulse were calculated analytically. It is shown that, in the process of interaction with the plasma, the laser pulse generates solitons propagating through the plasma layer and transferring the radiation through the opaque medium. The coefficient of transparency of the plasma layer for the soliton-like penetration of the laser radiation was calculated. The plasma parameters at which the collisionless absorption is small as compared to the transformation of the laser energy into solitons were found.
Keywords: 42.65.Tg; 52.35.Mw

Propagation of light through a forbidden zone in chiral media by E. V. Aksenova; A. A. Karetnikov; A. P. Kovshik; E. V. Kryukov; V. P. Romanov (909-919).
The particular features of the propagation of light in uniaxial chiral liquid crystals with a large pitch of the spiral are considered. There exist forbidden zones in these systems for fairly large angles of incidence of an extraordinary ray. On the one hand, this results in an efficient reflection of the wave from the zone boundary, and, on the other hand, this causes the wave to decay inside the zone. A case of narrow forbidden zones is studied, and it is shown that optical effects that arise upon propagation of rays near turning points are equivalent to the tunnel and over-barrier reflection effects. The angular dependences of the intensities of rays that were refracted in a forbidden zone and transmitted through it are calculated. The percolation effect is experimentally studied in a mixture of a nematic liquid crystal with a chiral addition. The intensity of a transmitted extraordinary ray is studied as a function of the angle of incidence, which determines the width of the forbidden zone. Both the over-barrier reflection and the percolation effects are observed. The calculation results are shown to agree with experiment.
Keywords: 42.70.Df; 42.25.Bs; 42.15.-i; 42.25.Fx; 42.25.Lc

On reflection of radiation from moving objects by Al. S. Kiselev; An. S. Kiselev; N. N. Rozanov; G. B. Sochilin (920-929).
An analytical expression for the field reflected from a nonuniformity of the velocity of a moving medium is obtained. Specific features of the reflected radiation depending on the velocity and sizes of the non-uniformity domain and on the angle of incidence of radiation relative to the direction of motion are studied. The feasibility of experimental detection of the reflected radiation is demonstrated.
Keywords: 03.30.+p; 03.50.De; 42.20.-q; 42.25.-p

Relaxation of an electrooptical effect in colloids induced by a field of short pulses by A. V. Voitylov; A. A. Spartakov; A. A. Trusov (930-934).
The possibility of studying the size distribution of particles suspended in a liquid irradiated with short pulses of strong electric fields, which almost do not change the properties of the disperse system is considered. The particle size is varied from 10 to 1000 nm. Relaxation dependences of the optically anisotropy induced by such pulses are investigated. The relaxation curves of the induced electrooptical effect are shown to behave similarly to the relaxation curves of the effect in the system with completely oriented particles. For aqueous polydisperse systems of diamond, graphite, and palygorskit, whose particles significantly differ in shape and physicochemical properties, the relaxation dependences of the electrooptical effect induced by fields of different duration and amplitude are measured. The correlation coefficients between the relaxation dependences are calculated. If the field is sufficiently strong, the correlation coefficients remain close to unity for all the three systems studied irrespective of the duration of the field pulse. This indicates that these curves are similar and that short powerful pulses can be used for determining the size distribution of particles in nanodisperse systems.
Keywords: 78.20.Jq

Postexposure sensitization of holograms on the basis of color centers in CaF2 crystals by incoherent radiation by A. S. Shcheulin; A. V. Koklyushkin; E. V. Tsygankova; A. I. Ryskin (935-939).
It has been reported about recording highly stable holograms on the basis of color centers in calcium fluoride crystals at a temperature of 200°C by UV light. In this study, holograms were recorded by visible light (4880 Å). The recorded holograms have a low diffraction efficiency, which can be significantly increased using postexposure irradiation of a sample by incoherent UV light at a temperature of 200°C. This increase demonstrates an important role of the drift component in the diffusion-drift mechanism of recording holograms based on color centers in ionic crystals.
Keywords: 42.70.Ln; 78.20.Nv

Changes in the optical refractive indices of a number of organic liquids, water, and some biological aqueous solutions exposed to (37.5–78)-GHz electromagnetic radiation have been investigated using a differential holographic interferometer. It is established that irradiation with intensities up to 10 mW/cm2 may reduce the refractive index of liquids by ∼10−3 as a result of thermal changes in the dielectric constant of the material studied. The magnitude and dynamics of changes in the refractive index are determined by the irradiation intensity and physical parameters of liquids (dipole moment of molecules, absorption coefficient, permittivity, and temperature coefficient of the refractive index) and are independent (within the experimental error) of the mutual orientation of the polarization unit vectors of the microwave and optical fields.
Keywords: 78.20.Ci; 78.20.Nv