Optics and Spectroscopy (v.89, #4)

High-efficiency conversion of the electronic excitation energy to the translational degrees of freedom in collisions of excited atoms with the surface of a solid by A. M. Bonch-Bruevich; T. A. Vartanyan; S. G. Przhibel’skiĭ; V. N. Smirnov; V. V. Khromov (487-489).
An experimental study is reported about the quenching of electronic excitation of Cs atoms caused by their collisions with a glass surface. The energy with which they are scattered from the surface after quenching has been measured to be 0.5 eV, which is about one-third of the excitation energy. A discussion is given of the mechanisms by which the excitation energy is partitioned between the atom and the surface in two different cases, namely, in the excitation of the atom adsorbed on the surface and in the collision of the preexcited atom with the surface.

The influence of fullerenes C60 and C70 on the optical characteristics of a promising organic system, N-(4-nitrophenyl)-(L)-prolinol (NPP), is studied. The UV and blue absorption bands are found that can be controlled by introducing fullerenes. These bands are caused by the change in the electronic structure of the organic system induced by fullerenes and indicate the presence of an ordering in the arrangement of macromolecules. The observed changes in the IR absorption result from the structural rearrangement of the system and may be related to a weak complexing between a donor fragment of the NPP molecule and fullerene. The effect of restriction of the nanosecond laser radiation at 532 nm is considered and characteristics of nonlinear transmission of laser radiation at 337 nm are presented. The levels of attenuation and incident energy are estimated, which determines the possibility of using results of these studies in the development of optical gates in a broad spectral range.

The Zeeman splitting of fine-structure levels of the 1snd configuration (n = 3, 4, 5, 6, and 7) of neutral helium in the magnetic field is calculated. The values of fields for level crossing and anticrossing are determined. Comparison with experimental data available in the literature is carried out.

Systematic calculations of the cross sections for excitation of the cadmium ion by low-energy electrons are carried out by the R-matrix method. The scattering strengths are computed in the approximation of strong coupling of channels with 15 terms of the 4d105s, 5p, 6s, 5d, 6p, 4d95s2, and 5s5p configurations taken into account within the framework of the LS-coupling scheme. Particular attention was given to the exact representation of the wave functions of a target in terms of the multiconfiguration Hartree–Fock method. The calculated cross sections exhibit a pronounced resonance structure, which makes an appreciable contribution to the total excitation cross sections, especially, for the 4d105s–4d95s2 transition. The results obtained are compared to the experimental data.

Rigorous expressions for the potential functions of a molecule in terms of the probability amplitudes of an electron transition are obtained. The results refine the formulas published in [13]. An algorithm for using these expressions for solving the inverse spectroscopic problem on the determination of the potential of a bound state of a diatomic molecule from the experimental spectrum of a bound–free electron transition from a selectively populated vibrational–rotational level is proposed. The potentialities of the method are demonstrated by the example of the analysis of the experimental continuum of the 23g + (v = 15, N = 27)→ a3u + transition in Na2. The possibilities for the extension of the expressions obtained to the case of polyatomic molecules and to the case of transitions where the combining states are not adiabatic are noted. Considerations on the question concerning uniqueness of the solution of the problem of determining the potential function from the experimental spectrum are advanced on the basis of the analysis of the expressions found.

The four-photon polarization spectra of the Rayleigh wing of water and its isotopic molecules are recorded in the frequency range from 0 to 50 cm–1. New resonances at ±1.4 (in H2O) and ±0.8 cm–1 (in D2O) are found whose nature is not clear as yet. It is shown that the HDO molecule has no rotational resonances in the 50% mixture of H2O and D2O, but H2O and D2O molecules exhibit distinct rotational resonances, which correlates with the data on valence vibrations.

Phototransformations of substituted p-terphenyl upon excitation by a XeCl laser by R. T. Kuznetsova; T. N. Kopylova; L. G. Samsonova; V. A. Svetlichnyĭ; E. N. Tel’minov (514-518).
Phototransformations of 1,8-dicarboxyisobutyl-substituted p-terphenyl in ethanol are studied upon excitation by a XeCl laser at a power density of up to 180 MW/cm2 for different types of radiation and different excitation geometries. The absorption and emission spectra are studied before and after irradiation. The resources of the lasing medium, quantum yields of phototransformations, and relative quantum yields of photoproducts are determined. The transmission of the solutions at the excitation wavelength and the shape of radiation pulses are measured as functions of the pump power density.

Calculations of the electronic structure of In, Ga, and Al impurity centers in a CdF2 crystal in the cluster approximation using the method of scattered waves are made. The first two impurities form in additively colored crystals bistable centers having a ground two-electron (deep) state and a metastable hydrogen-like (shallow) state. A change in the nature of the chemical bond on doping a crystal with these impurities is traced, which consists in a considerable increase of its covalent component. A change for deep In and Ga centers is shown to be caused by the reconstruction of centers in their ground state, and a conclusion about the character of reconstruction is made. This conclusion agrees with recent calculations made for the center structure using the pseudopotential method. Conditions of formation of bistable centers in CdF 2 and their structure in different charge states are discussed.

A method for analysis of polarization anisotropy of radiation and dichroism in crystals is proposed that is based on excitation of luminescence by the probe field having the form of a system of light bands with orthogonal polarization. The theoretical and experimental results concerning application of this method to the analysis of lithium fluoride crystals with radiation-produced color centers are presented. The specificity of optical microimage recording in crystals containing a collection of color centers is investigated.

The influence of heating on the spectral characteristics of pure alkali halide NaCl crystals by V. I. Kochubeĭ; Yu. G. Konyukhova; K. E. Gyunsburg; N. P. Zvezdova (531-534).
The influence of high-temperature heating on the spectral characteristics of pure natural NaCl crystals is studied. It is shown that defects changing spectral characteristics of crystals are formed in them when heated. Temperature dependences of the luminescence intensity growth for these defects are described by the hyperbolic function. The action of X-rays on heated crystals results in the formation of new defects luminescent in regions of 435 and 570–585 nm. The efficiency of formation of these defects is obtained as a function of the temperature of heat pretreatment. Regularities in variations of the location and the intensity of luminescence of the defects obtained under the action of ultraviolet radiation and on long storage are determined.

Spectroscopic Study of Neodymium-Doped Sodium–Yttrium Double Fluoride Nd3+:Na0.4Y0.6F2.2 crystals by S. É. Ivanova; A. M. Tkachuk; M.-F. Joubert; Y. Guiout; S. Gui (535-548).
Nd3+:Na0.4Y0.6F2.2 (Nd3+:NYF) crystals are grown by the Stockbarger–Bridgman method for a stoichiometric mixture prepared by the solid-phase method and containing neodymium up to 20 at. %. The absorption spectrum of Nd3+:NYF crystals exhibits bands located in the emission region of laser diodes. The peak absorption cross section of the 796.8-nm band is σ a = 0.96 × 10–20 cm2 and the bandwidth is Δλ = 17.5 nm. The most intense luminescence band is located at 1.05 μ m and the radiative time of the 4F3/2 level is τ0 = τexp ~ 960 μ s. It is shown that the 2P3/2 and 4D3/2 levels of Nd3+:NYF crystals are also radiative with lifetimes τ exp equal to ~110 and 9.5 μ s, respectively. However, these radiative transitions are partially quenched due to nonradiative relaxation. The intensity parameters Ω t are determined by the Judd–Ofelt method to be Ω2 = 1.18 × 10–20, Ω4 = 1.55 × 10–20, and Ω 6 = 2.85 × 10–20 cm 2. Using these parameters, the probabilities of radiative transitions and branching ratios are calculated, and the probabilities of nonradiative transitions are estimated. A conclusion is made that Nd3+:NYF crystals are promising as active media for diode-pumped tunable lasers, in particular, up-conversion-pumped lasers.

The nature of the long-wavelength region of the E0 photoreflectance spectra is studied in n - G aAs/ n + -GaAs homoepitaxial samples with n = 1015–1016 cm–3, n+ ≈ 1018 cm–3, and the epitaxial film width d = 1–5 μ m. The analysis of the published data, the quantitative analysis of experimental spectra, and our own experiments based on a novel technique, lead us to the conclusion that the low-energy oscillations originate in the electromodulation mechanism that takes place in the region of the film–substrate interface. The periodic modulation of the electric field near the film–substrate interface is induced by the isotropic diffusion of nonequilibrium minority carriers that are created in the neutral volume of epitaxial films under the action of laser excitation. The characteristic time constants of various photoreflectance components are estimated by combining the quantitative analysis of spectral line shapes with the analysis of experimental phase diagrams.

Cascade photon emission in luminophores by P. A. Rodnyĭ (556-562).
Cascade photon emission (CPE), i.e., the production of two or more photons of visible light upon excitation by a single vacuum UV photon, allows for the creation of luminescent materials with the quantum efficiency (Q) greater than unity. Various types of CPE, both experimentally observed and theoretically modeled, are described in this work. The basic characteristics of the matrix and the activator (a rare-earth ion) required for the CPE effect are determined. The most promising CPE materials are the Pr3+-activated fluorides with a high coordination number for the activator. It is shown that creation of phosphors with Q > 1, which is currently of great interest from both scientific and technological viewpoints, remains highly problematic.

The process of simultaneous absorption of three photons in a medium subjected to a three-photon parametric perturbation is considered. It is shown that in such a medium one can observe the formation of the radiation field states, which are the quantum superposition of three coherent components. One-photon and twophoton absorption processes in the medium also destroy the interference between the components of the superposition state. The states being formed are investigated in both the temporal development (numerically) and the stationary limit (numerically and analytically); the Wigner functions, as well as the quantum entropy, are calculated for a whole series of initial states. It is shown that depending on the initial state of the radiation field, the interference between the three-component superposition states being formed can lead, for example, to the almost total localization of the system in a two-component state or to the destruction of the interference between different coherent components.

Results of numerical simulation of collisions of two fundamental laser bullets—three-dimensional solitons formed in a medium with saturable amplification and absorption and frequency dispersion—are presented. A new collision regime resulting in the formation and the propagation of a switching wave is revealed. The existence of a metastable topological (with a wave front dislocation and an annular intensity distribution) three-dimensional dissipative optical soliton is demonstrated.

The Jaynes–Cummings model in the general nonresonant case without rotating-wave approximation is considered. The analysis is carried out using the resolvent formalism. It is shown that one, given the matrix of Hamiltonian resolvent, can easily find all basic physical quantities corresponding to the given model. The matrix of the resolvent of the total Hamiltonian for the given model is found. Matrix elements of the resolvent are expressed in terms of continued fractions. It is shown that these fractions uniformly converge to meromorphic functions, which corresponds to a purely point spectrum of the total Hamiltonian. The time evolution in the case of exact resonance for different coupling constants is numerically studied. It is shown that the rotating- wave approximation is not satisfactory for large coupling constants even in the case of exact resonance. In this case, probabilities of multiphoton transitions increase with increasing coupling constant.

The estimate of the magnitude of the magnetomechanical effect by M. P. Chaĭka; Tszin’ Shchego (589-592).
A formula for the calculation of the magnitude of the torque appearing in a glow discharge plasma when a magnetic field is applied is derived under certain assumptions.

Rational model of the human mechanism of color discrimination by E. I. Tolkova; A. V. Chernyshev (593-596).
Based on standard colorimetric data for people with normal vision and using an additional assumption about a rational construction of the color discrimination mechanism, the spectral sensitivities of human eye receptors are found, which virtually coincide with those measured experimentally.

The formation of a fine polarization structure of biospeckles of derma is studied. In the case of scattered laser radiation, the degree of polarization is shown to be an integrated characteristic of randomly distributed types and forms of polarization of an ensemble of biospeckles. A method for phase compensation of the degree of depolarization is proposed, which makes possible a severalfold increase of the measurement sensitivity.

The effect of a local field on the transition competition in the process of superradiance of a thin layer of three-level atoms (Λ-configuration of working transitions) in the presence of an initial coherence of the lower doublet is investigated. It is shown that under the action of a local field, a coherent Raman transition between sublevels of the lower doublet can take place.

Analysis of the form of ultrashort pulses by spectral nonlinear interferometry by Yu. T. Mazurenko; S. É. Putilin; A. G. Pel’menev; V. N. Shekhtman (612-618).
A new method for recording the phase structure of ultrashort optical pulses is proposed that makes no use of a reference pulse. Using three-wave interactions in a nonlinear optical medium, a wave of spectral decomposition of an ultrashort pulse is transformed into a monochromatic wave. The spatial phase structure of this wave contains information on the phase structure of the pulse spectrum and on the pulse form. This structure is analyzed by shearing interferometry.

The expression for the spectral power density of the static spatial optical noise (Wiener spectrum) in the light transmitted by a thin film of polymer-encapsulated ferroelectric liquid crystals is derived. Monodisperse half-spherical droplets of a bistable ferroelectric liquid crystal with a homogeneous planar orientation of directors are considered. Within the framework of the model of nonoverlapping disks, an analysis is performed concerning the influence of spatial correlation of the droplet positions on the shape of the noise spectrum and the signal-to-noise ratio during the realignment of the droplet director in an external electric field. The influence of misalignment of the droplet axes on the level of the static spatial optical noise is studied.

The influence of surface layers on reflection of light in the absence of absorption is studied. The contribution of an ultrathin N-layer film system to the light reflection coefficient is calculated by the smallparameter method within the framework of electrodynamics of continua. The angular dependence of the reflectivity in s- and p-polarization is analyzed, new possibilities for photometric diagnostics of ultrathin layers are demonstrated, and the extension of approximate Drude formulas to the multilayer case is presented.

Transmission and reflection of light normally incident on a layer of a medium with dielectric and magnetic helicities is studied. The axes of local tensors $$hat varepsilon$$ and $$hat mu$$ and the helix axis are parallel to one another and perpendicular to the boundary surfaces. Jones matrices are constructed. Reflection and transmission coefficients, the rotation of the plane of polarization, and the ellipticity of polarization are calculated. Specific features of natural polarizations and the character of reflection and passage of waves with natural polarizations are studied.

New formulas are obtained for the cases most frequently encountered in practice that allow one to find the number of reflections and the path length of a meridional ray in a hollow focon with a linear generatrix and a specular-reflecting inner side surface. By using a meridional-ray invariant, formulas were obtained that are free of any restrictions usually imposed on the focon conicity.

Chronicle (649-649).

Erratum: “Simulation of Scattering of Optical Radiation by a Metal Surface with Nanometer Irregularity” by A. Ya. Khaĭrullina; T. V. Oleĭnik; A. F. Sinyuk; V. A. Babenko; A. N. Ponyavina; T. A. Zhevlakova (650-650).