Optics and Spectroscopy (v.123, #5)

The restrictions on the choice of a moving coordinate system in the description of intramolecular dynamics are considered. These restrictions are imposed in order to make the obtained picture of intramolecular motions physically correct.

Nonadiabatic effects in (1~2)1Π–X1Σ+ rovibronic transitions of KRb molecules by S. V. Kozlov; E. A. Pazyuk; A. V. Stolyarov (676-681).
Numerical simulation of the effect of intramolecular electrostatic interactions on redistribution of relative intensities in the vibrational structure of (1 ~ 2)1Π–X1Σ+ rotationally resolved transitions of the KRb molecule is performed within the precision nonadiabatic model of coupled vibrational channels. It is established that mutual perturbation of electronically excited states modifies in a nontrivial way a nodal structure of nonadiabatic wavefunction of the (1 ~ 2)1Π complex, which is possible to use for rising efficiency of twostep laser synthesis and stabilization of ultracold ensembles of KRb molecules in the ground electronic state.

Direct and inverse spectroscopy problems concerning superposition of overlapping continuous spectral lines, as well as smoothing of the total spectrum by the instrumental function, are considered. The direct problem is formulated in two stages: initially, the total spectrum is formed by lines with a given intensity distribution, and, then, a smoothed by the spectrometer instrumental function and noisy spectrum is obtained. The inverse problem is also formulated in two stages: initially, the Fredholm integral equation of the first kind is solved by the Tikhonov regularization method (an ill-posed problem), and, then, the problem of reconstruction of separate line-component shapes from the total spectrum is solved, which is the problem of line separation (division). The individual line components are modeled by Gaussians and Lorentzians. Numerical illustrations are shown. Gaussian and dispersion (Lorentz) instrumental functions are considered.

Spectroscopy of He–Ne afterglow plasma by V. A. Ivanov; A. S. Petrovskaya; Yu. E. Skoblo (692-698).
The afterglow of pulsed low-current discharge in a He–Ne mixture is spectroscopically studied under conditions of competition between the processes of Ne2 + and HeNe+ dissociative recombination with electrons, which are the sources of population of excited levels of neon atoms. The behavior of neon spectral lines in the wavelength range of 350–850 nm corresponding to the transitions from the levels of neon atoms of the 2p 53p, 2p 53d, 2p 54p, 2p 54d, 2p55 s, 2p 55d, 2p56 s configurations are studied by the multichannel photoncounting method at electron density n e < 1011 cm–3 and helium and neon pressures P He = 38 Torr and P Ne ≈ 10-5 p He Distributions of recombination fluxes and population over excited states of the neon atom formed in the afterglow by homo- and heteronuclear ions are found. The data obtained show that vibrationally excited molecular ions make no noticeable contribution to the spectrum of decaying He–Ne plasma.

Dynamics of luminescence spectra of photoexcited electron donor–acceptor complexes in a Debye solvent has been investigated within the Bixon–Jortner model. It has been shown that the main factors affecting the spectral dynamics in highly exergonic systems at times of up to several picoseconds are intramolecular vibrational relaxation in reactants and relaxation of solvent in the vicinity of an ion pair. Exact solutions of the mathematical model are obtained for two cases in which one relaxation channel dominates over another. The influence of the intramolecular reorganization energy on the luminescence-band profile at short times has been analyzed.

The features of nonradiative resonance energy transfer in hybrid associates of colloidal CdS quantum dots (QDs) with molecules of a thiazine dye and J-aggregates of a carbocyanine dye are discussed. The case of an inhomogeneously broadened recombination band of donor (CdS QDs) luminescence is considered. We detected spectral-selective quenching of recombination luminescence of colloidal CdS QDs in association with organic dyes. The maximum of quenching occurs in the region of absorption of the acceptor (organic dye molecule). It is shown using the time-correlated single photon counting technique that the lifetime of the QD luminescence decreases synchronously with the quenching of the luminescence, but only at the wavelengths falling in the region of absorption of the dye. Based on the concept of a donor–acceptor nature of emission of CdS QDs, the dependence of the efficiency of nonradiative energy transfer on the luminescence wavelength is analyzed taking into account the Poisson distribution of its quenchers.

The infrared (IR) and Raman spectra of three samples of fluorapatite single crystals and carbonate fluorapatite single crystal in the region of 7000–400 cm–1 were studied. It has been shown that isomorphic substitution of the Ca2+ cation and the PO4 3- anion leads to an increase in the size of the c-channels in the apatite crystal, which is accompanied by the formation of water clusters of the (H2O) n and H3O+ · (H2O) n (n = 2–5) types as a result of the diffusion processes in these local sections of the c-channels.

Dispersion of the refractive index in high-k dielectrics by V. A. Shvets; V. N. Kruchinin; V. A. Gritsenko (728-732).
A brief review of the optical properties of oxide materials that are used at present as dielectrics in modern microelectronics is presented. Using spectral ellipsometry, dispersion dependencies for different materials are measured. A brief comparative analysis of different dielectric coatings is carried out. The results of our research will be useful in further studies of the properties of dielectrics, as well as in technologies that are employed in the development of new semiconductor instruments and devices.

Luminescent properties of solid solutions in the PbF2–Euf3 system and lead fluoroborate glass ceramics doped with Eu3+ ions by T. S. Sevostjanova; A. V. Khomyakov; M. N. Mayakova; V. V. Voronov; O. B. Petrova (733-742).
Lead fluoroborate glasses doped with Eu3+ are synthesized, studied, and used to produce glassceramics by heat treatment. The structure of glass-ceramics is determined by X-ray diffraction. The optical, mechanical, and luminescent properties of the glass-ceramics are studied. The structure and spectral-luminescent properties of solid solutions in the PbF2–EuF3 system obtained by both solid-phase reaction and coprecipitation from solutions are investigated.

The effect of elastic strain on the dispersion characteristics of a polariton 2D structure by V. V. Rumyantsev; S. A. Fedorov; K. V. Gumennyk (743-749).
The dispersion characteristics of a two-dimensional lattice of tunnel-coupled micropores containing single-level quantum dots are numerically simulated. It is shown that, as a result of elastic strain of the system under study, it is possible to achieve necessary changes in its energy structure and optical properties determined by the rearrangement of the polariton spectrum.

Luminescent mixed-ligand Eu(III) complexes with quinaldic acid and nitrogen-containing dimeric ligands are synthesized. The thermal and spectral-luminescent properties of the obtained mixedligand Eu(III) complexes are studied. It is shown that a water molecule and a neutral ligand are detached during thermolysis in two stages with endothermic effects. It is found that the quinaldinate ion is coordinated to a europium(III) ion in a bidentate fashion. The Stark structure of the 5D 0–7F j (j = 0, 1, 2) transitions in the low-temperature luminescence spectra of europium(III) complexes is analyzed.

Kinetics of relaxation of photoluminescence from the interband transition between dimensionalquantization levels of electrons and holes in InGaAs/GaAs quantum wells as a function of their distance to an interface with Au is investigated. It is demonstrated that the photoluminescence relaxation time becomes several times shorter when the distance from the quantum well to the interface decreases to several tens of nanometers. It is established that the photoluminescence relaxation time at a shorter wavelength corresponding to a recombination transition between excited states of electrons and holes in the quantum well is shorter than that at a longer wavelength corresponding to a recombination transition between the ground states. A theoretical model explaining this phenomenon is proposed.

We review the studies of the spatial conditions for the quasi-phase-matching in the multi-jet laserproduced silver plasma. These studies of the off-axis and on-axis spatial components of harmonics allowed the demonstration of significant enhancement of a group of harmonics in the latter case. We analyze the role of plasma emission, together with phase-mismatch, that deteriorate the conditions of high-order harmonic generation due to significant phase distortion between the interacting waves. We also discuss the resonanceinduced enhancement of single harmonic and the quasi-phase-matching-induced enhancement of the group of harmonics during propagation of the tunable mid-infrared femtosecond pulses through the perforated laser-produced indium plasma. Those studies have shown that the enhancement of harmonics using the macro-process of quasi-phase-matching is comparable with the one using micro-process of resonantly enhanced harmonic. We conclude that joint implementation of the two methods of the increase of harmonic yield could be a useful tool for generation of strong short-wavelength radiation in different spectral regions.

Possibilities of standard multiangle monochromatic ellipsometry in the determination of parameters of a uniform biaxially anisotropic layer are studied for the case of an arbitrary orientation of the two principal axes in the plane of incidence of the light beam and perpendicularity of the third axis to the plane of incidence. Using numerical simulation, it has been found that the measurement accuracy that is necessary in the determination of all the three principal components of the dielectric permittivity tensor ε and tilt angle of the axes using only angular dependences of ellipsometric parameters must be no worse than 0.0001°, which is far beyond the accuracy limits provided by present-day ellipsometers. If the tilt angle is known, standard multiangle monochromatic ellipsometry provides the determination of thickness and all three principal components of the dielectric permittivity tensor. This method allows one to determine the layer thickness and tensor component for the axis perpendicular to the plane of incidence, as well as the average value of components for the axes lying in the plane of incidence without involving the data about the tilt angle of the axes. This is demonstrated by an example of experimental data for biaxially anisotropic SiO x films obtained by oblique deposition of silicon monoxide SiO evaporated in vacuum.

The propagation of a light pulse through a layer of a substance with population inversion and, correspondingly, with an anomalous dispersion in the transparency range is considered. It is shown that, when the wave packet approaches the layer of the substance with a strong anomalous dispersion, two additional wave packets arise at the rear boundary of the layer. One of these packets has a negative energy and moves in the layer from its rear to the front boundary, while the other packet moves away from the rear boundary of the layer into a vacuum. As the initial wave packet comes into contact with the front boundary of the layer of the substance, it meets the packet of the negative energy. As a result, the two packets annihilate one another, after which only one packet remains, which moves away from the layer.

The inferences of a paper by N.S. Bukhman on the appearance of waves with opposite directions of the phase and group velocities in a layer of an amplifying medium (Opt. Spectrosc. 123 (5), 783 (2017)) are analyzed. It is shown that these inferences need additional substantiation.

Optimization of sensors based on surface waves in flat-layered structures by A. B. Petrin; O. D. Vol’pyan; A. S. Sigov (798-802).
A method for increasing the sensitivity of surface-wave sensors in multifilm structures is proposed based on the results of a theoretical study of the reflection of a plane electromagnetic wave from a flat-layered structure containing homogeneous films. A method for optimizing the parameters of the films forming the surface structure is developed and tested. The devices proposed are characterized by high field amplification in a surface layer of multifilm structure and a higher sensitivity to variations in the optical properties of the thin near-surface layer. Application of the proposed multifilm structures is expected to increase significantly the sensitivity of the existing sensors based on surface-plasmon polaritons, which are applied in modern optical multichannel biological, chemical, and physical sensor systems.

Concentration of energy inside laser-irradiated gold and silver plasmon nanoparticles in air by L. G. Astafyeva; V. K. Pustovalov; W. Fritzsche (803-808).
We simulated laser-intensity distribution inside spherical gold and silver nanoparticles with radii between 10 and 100 nm, which are exposed to laser radiation at 400, 532, and 800 nm in air, and analyzed the results. The effect of high energy concentration inside illuminated (front) and shadowed (back) hemispheres of gold and silver nanoparticles is established for several nanoparticle sizes and laser wavelengths. The results can be used in nanophotonics of new plasmon devices (concentrators, antennas, etc.) and photon components.

The photocatalytic activity of some metal oxides and sulfides, as well of С60 fullerene, is compared using the method of photocatalytic degradation of methylene blue simultaneously with comparison of the efficiency of methylene blue adsorption on solid-phase powders of these oxides, sulfides, and fullerene in aqueous solution of the dye in the absence of irradiation.

Particular features of the band structure of one-dimensional apodized photonic crystals based on metamaterials are studied in the case in which the medium is simultaneously inhomogeneous with respect to both the dielectric and the magnetic properties. It is shown that in the case of oblique incidence of light at large values of the modulation depth, a new region of diffraction reflection appears. This new region of diffraction reflection is also observed at magnetic permeability μ = const = 1. The particular features of the absorption and localization of light in these structures are examined.

Long-term luminescence of sensibilizers in tissues at the conditions of oxygen deficiency due to photodynamic effect by A. T. Ishemgulov; S. N. Letuta; S. N. Pashkevich; E. K. Alidzhanov; Yu. D. Lantukh (828-834).
Long-term luminescence of organic dyes (xanthene dyes, halogen substituted fluoroscein) was used for an in vitro study of the photodynamic effect of exogenic probes in malignant tumors and healthy tissues of mice. It is shown that the photodynamic activity of oxygen and the dynamics of its concentration in tissues can be estimated from the delayed fluorescence of exogenic probes caused by singlet–triplet annihilation of singlet oxygen and excited triplet states of the molecules of photosensitizer dyes. It is found that quenching of long-term luminescence of photosensitizers significantly differs in tumors and normal tissues.