Vol 127, No 1 (2019)

Förster resonance energy transfer (FRET) is examined in a single donor (D)–acceptor (A) pair whose molecules have both singlet and triplet states. Two cases are considered: (i) the excitation of the D–А pair occurs with the participation of a singlet band of the donor, and (ii) the excitation also involves the participation of an additional triplet–triplet absorption. The triplet state of the donor is shown to have no effect on the expression for the FRET efficiency, but it generates off intervals in the fluorescence track of both the donor and the acceptor. The triplet state of the acceptor strongly affects the expression for the FRET efficiency, making the complete energy transfer impossible and generating off intervals in the acceptor fluorescence track. It is shown that, if the light can excite not only the singlet transition in the donor, but also the triplet–triplet absorption band, then a weak luminescence appears in off intervals, which is orders of magnitude weaker than that in on intervals.

We have measured the polarized Raman scattering and IR reflection spectra of a BaGa₂GeS₆ crystal, the Ga and Ge atoms of which are disordered, randomly occupying crystallographic positions of the same kind. The IR reflection spectra have been processed by the dispersion analysis method. The dispersion of phonons, the density of phonon states, the electronic band structure, and the partial densities of electronic states have been calculated in the DFT approximation using the alchemical potential method for disordered Ga and Ge atoms. It has been found that the stretching vibrations in the vibrational spectra are separated from the bending modes by a gap of about 100 cm^–1 and that the band structure of the crystal has an indirect energy gap.

High-resolution low-temperature absorption spectra in the region of the ⁵I₈ → ⁵I_{7, 6, 5, 4}, ⁵F₅ transitions in impurity Ho³⁺ ions in synthetic forsterite crystals (Mg₂SiO₄) are recorded. Comparison of the observed shape of the spectral lines with the hyperfine structure calculated using crystal-field theory makes it possible to attribute the spectral lines to single centers and dimers for the first time.

The reflection and attenuated total reflection spectra of aluminum and gallium nitride films doped with silicon on sapphire substrates with a buffer layer of aluminum nitride have been measured. In the spectra of attenuated total reflection, surface phonon and plasmon–phonon polaritons were observed. A high concentration of charge carriers in the gallium nitride film and their practical absence in the aluminum nitride film were experimentally observed.

A review of the works that we have been carried in the last 5 years on the use of the method of absorption spectroscopy with diode lasers for the diagnosis of hot zone parameters is given. A spectrometer with two lasers operating in different spectral ranges with sufficiently strong absorption lines has been developed for the case of high pressures and gas temperature. The results of the search for optimal lines in different spectral ranges have been presented. The results of laboratory measurements and tests at the experimental power stand at TSAGI Named after Prof. N.E. Zhukovsky have been presented. Approaches to determining the maximum temperature for spatially inhomogeneous hot zones have been discussed. The method of difference spectra and method of fitting the experimental spectrum with the sum of one-temperature spectra have been proposed. The efficiency of the proposed processing algorithms for specific types of hot zones has been shown experimentally.

The paper presents a brief review of recent works concerning the modeling of X-ray lasers in cluster flows and in nanostructured targets. Calculations of the atomic characteristics are based on relativistic perturbation theory with a model potential of zero approximation. Two new results are discussed: (1) it is shown that a subpicosecond X-ray laser with λ = 41.8 nm formed in a xenon cluster flow can serve as an alternative to a free-electron laser and (2) in heavy Ni-like ions (Z ≥ 60), the ionization of ions and recombination of electrons are balanced at electronic temperatures ≥1500 eV; thus, the state of a Ni-like ion is quasi-steady-state. The inversions of many transition levels of an X-ray laser are also quasi-steady-state. The possibility of experimental observation of X-ray lasers based on 3p⁵4d¹⁰4p [J = 0] – 3p⁶3d⁹4p [J = 1] intrashell transitions in Gd³⁶⁺ with wavelengths in the water window region is discussed.

The radiation intensity redistribution of the probe field upon its scattering by spatially periodic atomic population gratings in a medium with a four-level tripod configuration of atomic states is investigated theoretically. Conditions are found under which a significant redistribution of the probe-wave field intensity occurs, and a “diffraction” pattern is formed with an efficient probe-field intensity transfer to the first-order maxima.

A review of results of an investigation of the theory of optical wave packets with extreme properties with respect to a controllable pulse shape or to the complexity of the internal structure of radiation beam pulses is presented. Special attention is paid to the manifestations of dissipative effects of the electromagnetic energy inflow and outflow. Precisely these factors lead to peculiar rules of conservation of purely electromagnetic quantities in dissipative media, in which the electromagnetic energy irreversibly decreases in the case of absorption and increases with gain. These rules impose certain restrictions on the possibility of transformation of the shape of pulses and allow one to qualitative describe their evolution. A higher efficiency of the action of unipolar or quasi-unipolar radiation pulses on classical and quantum microobjects is shown and possible ways of formation of these pulses are discussed. For bulk laser media with saturable absorption, the topological properties of localized radiation structures and their transformations with a smooth change in the parameters of the medium (pump level) are described. The preservation of the topological structure upon changes in parameters within the stability range yields the possibility of their distinguishing when coding information by topological solitons of the considered type.

The evolution of high-intensity light pulses in nonlinear single-mode optical waveguides, the dynamics of light in which is described by the nonlinear Schrödinger equation with a Raman term taking into account stimulated Raman self-scattering of light, is investigated. It is demonstrated that dispersive shock waves the behavior of which is much more diverse than in the case of ordinary nonlinear Schrödinger equation with a Kerr nonlinearity are formed in the process of evolution of pulses of substantially high intensity. The Whitham equations describing slow evolution of the dispersive shock waves are derived under the assumption of the Raman term being small. It is demonstrated that the dispersive shock waves can asymptotically assume a stationary profile when the Raman effect is taken into account. Analytical theory is corroborated by numerical calculations.

Luminescence spectra of single crystals of rare-earth gallium borates LnGa₃(BO₃)₄ (Ln = Nd, Sm, Tb, Er, Dy, or Ho) at room (300 K) and cryogenic (10 K) temperatures are presented for the first time. Photoluminescence has been recorded in the wavelength range of 470–5000 nm (2000–21 300 cm^–1) with a high spectral resolution (down to 0.1 cm^–1) upon excitation by different diode lasers. The spectra obtained cannot be unambiguously interpreted within one luminescent center, which can be due to the presence of defects and/or inclusions of other crystalline phases. The optical nonlinearity of rare-earth–gallium borates has been estimated using the Kurtz–Perry powder technique. The typical intensities of the second-harmonic generation in gallium borate powders are 30–40 (with respect to quartz), and the optical nonlinearity is as good as the nonlinearity of the efficient rare-earth aluminum borate YAl₃(BO₃)₄.

The effect of an organic dye deposited on the surface of a semiconductor on the photo-EMF spectrum in monocrystalline silicon has been studied. Sensitization of the internal photoeffect has been found in the semiconductor in the absorption band of the dye. An optimal concentration of the dye on the semiconductor surface that corresponds to a dye film thickness of 10–15 nm has been determined. The mechanism of sensitization is discussed on the basis of the theory of nonradiative inductive-resonant energy transfer from the dye to the semiconductor.

Laser-induced nanocluster structures of different types (in topology and in elemental compositions of noble metal/carbon, bimetals, semiconductors, etc.) are studied theoretically and experimentally with allowance for the correlations in an ensemble of nanoparticles with quantum size states. The problem of high-temperature superconductivity (in the form of a sharp decrease in electrical resistivity) caused by topological surface structures leading to bound states of electrons based on new dimensional principles is discussed.

Fatty acid triglycerides are essential components of the human diet, while possessing unique biological activity. Their content in biological media is traditionally determined by gas and liquid chromatography. They are not readily available for mass analysis of food products and blood serum due to the complexity of these methods. The aim of our work is to study the correlation of the absorption spectra of near-infrared radiation with the characteristic oscillations of functional groups of clinically important fatty acids, such as palmitic saturated ones and oleic and linoleic unsaturated ones, as well as their trans-isomers, as well as to develop techniques and test equipment for rapid assessment of their content in fat products and blood serum. As a result, evidence of the applicability of the Fourier spectrometer in the wavelength range of 1.0–2.4 μm for the operational analysis of clinically important fatty acids in butter, spreads and serum, as well as the correlation of the absorption spectra of serum with the content of total triglycerides and cholesterol were revealed. In addition, using a portable spectrometer in the wavelength range of 1.0–1.65 μm suitable for mass analysis of fat-and-oil products quality, the content of these fatty acids was determined, and the selectivity of their determination was studied.

Diagnostic pilot monitoring of the groups of healthy patients and patients with colorectal cancer (CRC) at different stages of the disease was carried out using Raman spectroscopy (RS) and measuring the state of polarized light near the conditions of observation of surface plasmon resonance (SPR). The reaction of the blood serum antigens with antibodies to serum M2 pyruvate kinase (M2-PK) nears the conditions of observation of SPR was used for diagnosing; for this, the Ellipse-SPEC spectral ellipsometric complex created at the Rzhanov Institute of Semiconductor Physics (Siberian Branch, Russian Academy of Sciences) and having a high sensitivity, accuracy, and nondestructive nature of the effect on the studied sample, was used in the work. The peak intensities at 1005, 1157, and 1520 cm^–1 in Raman spectra in CRC patients as compared with healthy individuals (as well as the intensity of surface plasmon resonance) were significantly lower, correlating with the stage of the disease and the presence of metastases; this allows to consider these optical methods for studying the blood serum as promising diagnostic approaches in diagnosis CRC, including in the early stages of the disease.