ISSN (print): 0030-400X, ISSN (online): 1562-6911 Главный редактор: Розанов Н.Н. Издатель: Физико-технический институт им. А.Ф.Иоффе РАН Входит в: Белый список (уровень 2), Scopus, Web of Science (SCIE)
Физико-технический институт им. А.Ф.Иоффе РАН
The Use of IR Spectroscopy and Density Functional Theory for Estimating the Relative Concentration of Triglycerides of Oleic and Linoleic Acids in a Mixture of Olive and Sunflower Seed Oils
Infrared spectra of five samples of sunflower seed oil and five samples of cold-pressed olive oil of different brands are recorded in the range of 650–3800 сm–1. The structural models of eight fatty acids (oleic, linoleic, palmitic, stearic, α-linolenic, arachidonic, eicosapentaenoic, and docosahexaenoic), as well as of triglycerides of the first four of these acids, are constructed using B3LYP/6-31G(d) methods. The vibrational wavenumbers and intensities in the IR spectra are calculated. The IR spectra of olive and sunflower seed oils are simulated using the supermolecular approach. The dependence of the intensity of vibrational bands at νexp = 914 and 3009 сm–1 on the concentration of triglycerides of oleic and linoleic acids in oils, as well as on the saturation degree of fatty acids, are studied. Experimental and empirical dependences are plotted to estimate the relative concentrations of triglycerides of oleic and linoleic acids in mixtures of olive and sunflower seed oils. The applicability of the density functional theory in combination with IR spectroscopy for characterization of vegetable oils is discussed.
Helium Afterglow without Metastable Particles
We study the afterglow of a pulsed barrier discharge in helium with a small admixture of neon (10‒2%), which creates a plasma with a low density of metastable particles. The early afterglow of this discharge is free of processes involving the participation of metastable particles and has a purely recombination nature. The characteristics of the afterglow are interpreted based on a model taking into account vibrational kinetics and dissociative recombination of \({\text{He}}_{{\text{2}}}^{ + }\) molecular ions. Comparison of experimental data and model solutions for fluxes of collisional–radiative recombination of He+ ions with electrons and dissociative recombination leads to the conclusion that the latter process is more likely to be a source of the formation of excited atoms.
The VoTe Room Temperature H216O Line List up to 25 000 cm–1
A new line list transition for the water molecule is presented. The line lists is created on the basis of VoTe calculations using cutoff values of 25 000 cm–1 in transition wavenumber and J max = 50. Calculations use the high accuracy, empirical potential energy surface (PES) of Bubukina et al. LTP2011 and the CVR water dipole moment surface (DMS) of Lodi et al. (2011). Vibration–rotation energy levels up to J = 50 are computed using DVR3D; a novel method of labeling is used which allows more thorough labelling of the energy levels with approximate vibrational and rotational quantum numbers than previous water line lists.
Resonance Energy Transfer Rate in the Presence of a Cylindrical Photonic Band-gap Structure
The resonance energy transfer rate between an excited atom and a ground-state one depends on various factors such as the matching between the donor and acceptor wavelengths, location of the atoms, and the environment that surrounds them. We investigate the interatomic resonance energy transfer rate in the presence of a cylindrical dielectric multi-layer structure using the Green’s tensor formalism. The permittivities of the layers are interchanged periodically between low and high values, so as to create a photonic band-gap system in the radial direction. We present results for atoms situated in a cross section normal to the cylinder axis. The contrast between low and high permittivities is varied to elucidate the effect of the band-gap structure. Furthermore, the results are compared with those for atoms located near a perfectly reflecting c-ylinder.
A Study of Low-Energy Processes in Polymethyl Methacrylate and Its Short-Chain Oligomers by Terahertz IR and Raman Spectroscopies
Based on the data of low-frequency (terahertz) IR and Raman spectroscopies, it is established that low-energy vibrational excitations in PMMA and its oligomers with a degree of polymerization n = 2, 7, 9, and 50 are due to correlated small-angle torsional–vibrational dynamics, which prepares the relaxational mobility of macromolecules. The minimum size of the chain segment (“torsional–vibrational segment”), the spectrum of which is identical to the spectrum of the high-molecular polymer, is determined.
The Structure and Vibrational Spectra of Gallium(III) Fluoride Dimeric Complex with Tetramethylammonium Cation
We have determined the crystal structure of gallium(III) fluoride dimeric complex [N(CH3)4]2[Ga2F8(H2O)2], which is composed of [N(CH3)4]+ tetrahedral cations and [Ga2F8(H2O)2]2– dimeric complex anions, formed by combining two slightly distorted GaF5(H2O) octahedral groups with a common F–F edge. By O–H···F hydrogen bonds, [Ga2F8(H2O)2]2– dimeric complex anions unite into polymer chains, between which tetramethylammonium cations are located. Based on quantum-chemical calculations, we have assigned bands in vibrational spectra of the synthesized compound. Bands that refer to vibrations of anions, cations and H2O molecules involved in hydrogen bonds have been identified in the spectra.
A Spectrophotometric Study of Nitrate and Nitrite Salts and Their Aqueous Solutions
Optical characteristics of nitrate and nitrite salts and their aqueous solutions are studied to demonstrate the application of direct spectrophotometric methods for determination of different forms of nitrogen salts in water. Examples of application of the method for determination of nitrate ion in samples of natural and drinking water from wells are given.
Investigation of the Hydrophility of a Polyurethane Film by the Photoelasticity and Nuclear Magnetic Resonance Relaxometry Methods
The method of optical polarimetry has been used to study the hydrophilicity of polyurethane. It has been shown that swelling of the elastomers increases the initial optical anisotropy and decreases the photoelasticity coefficient. The change in optical anisotropy at deformation of polyurethane under conditions of a long-term action of constant force has been investigated. The nuclear magnetic resonance relaxometry method with an integral transformation inversion has been used to study the effect of polyurethane swelling on the dynamics of elastomer macromolecules.
A Spectroscopic Study of Changes in the Secondary Structure of Proteins of Biological Fluids of the Oral Cavity by Synchrotron Infrared Microscopy
On the basis of the data of infrared spectroscopy with synchrotron radiation, the secondary structure of proteins of the dentinal and gingival fluids during the development of cariosity in deep dentin tissues is studied. It is shown that the change in the shape of the profile of the amide I band in the region of 1700‒1605 cm–1 is associated both with a change in the ratio of the integrated absorption intensities of the α‑helix and β-sheet secondary structures and with the position of the β-coil and β-sheet components in the spectrum. It is established that the α-helix/β-sheet ratio for both dentinal and gingival fluids is below the threshold level, at which significant changes in the secondary structure of proteins of biological fluids are observed, unequivocally indicating the development of pathology in hard dental tissues. The features that we discovered in the profile of the amide I band of biological fluids of the oral cavity, together with the spectral markers of the development of cariosity in dentin, are reliable spectroscopic signatures of the pathology and can be detected using the gingival fluid.
Synthesis and Luminescent Properties of Gadolinium Tantalum Niobates Gd(NbxTa1 – x)O4
The feasibility of synthesizing gadolinium tantalum niobates by the liquid-phase method was demonstrated. The methods of X-ray diffraction, electron probe microanalysis, local cathodoluminescence, and photoluminescence were applied to study the samples. It was shown that under the selected synthesis conditions (T ~ 1400°C for 3 hours), no solid solution of niobium-tantalum was formed in the powder samples. When obtaining ceramic samples, it was possible to obtain a solid solution and to study the dependence of the luminescence intensity on the niobium content upon excitation of the samples by an electron beam. The maximum luminescence intensity was observed in the sample with the composition of GdNb0.9Ta0.1O4. It was shown that the inhomogeneity of luminescence is not related to fluctuations in composition, but is related to the inhomogeneous distribution of vacancy centers, which are luminescence centers.
Anisotropy of IR Absorption of an Ultrathin Water Layer on a Water/Quartz Glass Interface
The optical properties of an ultrathin water layer at the interface between two dielectrics (ZnSe–SiO2) are studied by FTIR spectroscopy. Effective refractive indices and absorption coefficients in the region of stretching vibrations of the OH group are determined. It is found that water molecules in the water–quartz glass interface layer have a planar orientation.
Pressure-Induced Changes in Parameters of the Indicatrix of Lithium Sodium Sulfate Crystals
Spectral, temperature, and baric dependences of birefringence Δni of LiNaSO4 (LSS) crystals have been studied. It is established that dispersion Δn(λ) is anomalous. It is shown that uniaxial compression leads to changes in Δnі with different magnitudes and signs. The dispersion effect of changes in Δnі decreases under stress \(\sigma \, \bot \, z\) and increases in the opposite case (σ || z). Pressure-induced changes in the refractive index are estimated; it is established that the refractive indices of an LSS crystal increase under uniaxial compression, which may be related to compression of the crystal and change in its interatomic bond nature.
Exact Solutions for the Local Parameters of Polarization Modes in Coiled Optical Spun Fibers with Strong Unperturbed Linear Birefringence. I. Nonresonant Linear Transformation
The propagation of monochromatic radiation in coiled spun optical fibers is considered. The local parameters of the elliptical polarization eigenmodes, elliptic birefringence, and the ellipticity angle are the sum of the constant and variable components, with the latter being measured almost according to the harmonic law depending on the length of the fiber. The magnitudes of the constant components are significantly higher than the amplitudes of the variable components. The dependence of the local azimuth of the major axis of the ellipse of the polarization eigenmodes increases almost linearly.
Solution of the Problem of Diffraction by a Body of Revolution Located in a Dielectric Layer
Two methods for solving the problem of diffraction of a plane wave by a dielectric body of revolution located in a homogeneous dielectric layer are proposed. The methods are compared with each other using as an example the solution of the problem of scattering of a plane wave by a homogeneous spheroid and a circular cylinder of finite dimensions located in the layer. The results of calculations of the scattering diagram for the case of diffraction by a finite circular cylinder that is immersed into the layer and has variable material characteristics are presented. The dependences of the scattering diagram on the wavelength for plasmon particles located in a layered medium are obtained.
Reflection of Light from a Layer of a Hyperbolic Metamaterial
We have investigated specific features of reflection of a plane elliptically polarized electromagnetic wave that is incident from an isotropic nonabsorbing medium onto a plane-parallel layer of a hyperbolic metamaterial the optical axis of which is parallel to the interface, while the diagonal values of the dielectric permittivity are smaller than the dielectric permittivity of the isotropic medium. Depending on the angle of incidence and the angle between the plane of incidence and the optical axis of the hyperbolic metamaterial, regimes are possible in which either an ordinary wave or an extraordinary wave, or both waves decay outward from the interface, and, in the latter case, for some values of these angles, the decay may be nonexponential. For these three regimes, the reflection coefficient from a layer of an ITO/Ag nanostructure has been calculated numerically. Upon variation in the polarization of the incident wave, the energy reflection coefficient changes from minimum to maximum values, which depend on the layer thickness. As distinct from conventional anisotropic media, in all cases, the maximum value of the reflection coefficient tends to unity with increasing layer thickness. If the amplitude of an ordinary or extraordinary wave does not decrease outward from the interface boundary, the minimal reflection coefficient periodically turns to zero with increasing layer thickness due to interference. In the case in which both waves decay, with this decay being nonexponential under certain incidence conditions, the minimum reflection coefficient turns to zero at a certain layer thickness, and then tends to unity.
Transportation of Extremely Short Radiation Pulses in a Waveguide with a Nonsimply Connected Cross Section
Specific features of the transportation of extremely short radiation pulses in a metal waveguide are analyzed. It is inferred that the mode dispersion can be suppressed, thereby preserving the shape of pulses, including subcycle and unipolar pulses, at distances limited by the absorption in the metals.
Optical Gain in Laser Heterostructures with an Active Area Based on an InGaAs/InGaAlAs Superlattice
An active area based on InGaAs/InGaAlAs superlattice for laser diodes operating in the spectral range between 1535 and 1565 nm is proposed and realized practically. It is demonstrated that using a superlattice increases the mode gain at the same values of the pump-diode current density relative to a typical active-area design based on an array of InGaAs quantum wells.
Multiple Parameters Optical Sensing Using Fiber Ring Laser Based on Fiber Bragg Gratings and 1064 nm Semiconductor Optical Amplifier
In this paper, a semiconductor optical amplifier (SOA) based 1064 nm fiber ring laser with 63.56 dB optical signal-to-noise ratio (OSNR) is demonstrated. The stable performance is measured for six hours with lasing peak variation of ≤±0.115 dB and wavelength variation of ≤±0.006 nm. Combining the fiber ring laser with fiber Bragg gratings (FBGs), the SOA based fiber ring laser is applied to sense stretch, squeeze, and temperature variation. The results show high linearity, which is suitable for interpolation method prediction and evaluation. A large dynamic range of up to 10 km is also demonstrated for remote sensing applications.
Radiation of a Resonant Medium Excited by a Periodically Phase-Modulated Laser in the Regime of Strong Coupling between the Field and the Matter
The radiation of a two-level resonant medium that is placed into a cavity and is excited by a periodically phase modulated laser pulse is studied theoretically. The radiation is analyzed based on the analytical and numerical solutions of the system of Maxwell–Bloch equations under conditions of a strong coupling between the field and the matter. Under these conditions, this system is similar to a polariton laser. The excitation efficiency of a polariton laser by a phase-modulated radiation pulse is shown to be high compared to a pulse without phase modulation of the carrier frequency. It is shown that the main reason for the efficient excitation of polariton modes in the medium is the appearance of difference combination parametric resonance. The obtained results open up new possibilities for the excitation of radiation of polariton lasers by low-power frequency-modulated pump laser radiation.
Quantum Squeezing of the Field of a Single-Atom Laser under Conditions of a Variable Coupling Constant
A nonstationary regime of squeezed-light generation by a single-atom laser is investigated. Dependences of the quantum-squeezing parameter and radiation intensity on modulation frequency of the atom–field coupling constant are obtained. It is demonstrated that a resonance appears at the modulation frequency equal to twice the average coupling constant, which leads to a more efficient quantum squeezing in a nonstationary harmonic regime than in the case of a stationary regime for the same values of the relaxation and pump parameters.
X-Ray Luminescence of Zinc Oxide Thick Films
Samples of thick (about 30 μm) films of undoped zinc oxide on sapphire prepared by magnetron sputtering using an uncooled target have been investigated. The structural and luminescence properties of the initial films and films subjected to additional recrystallization annealing in air have been studied. The time and temperature-dependent characteristics of the samples are considered. It is shown that annealing in air enhances the structural, optical, and luminescence properties of these films.
Optical and Photoluminescent Properties of Thin-Film ZnO–PLZT Structure in the UV and Visible Spectral Regions
The structural, optical, and photoluminescent properties of the thin-film structure ZnO–PLZT ferroelectric ceramics are studied. The results of X-ray diffraction analysis for a zinc oxide film synthesized on PLZT and quartz substrates are reported. The transmission, reflection, absorption, and photoluminescence spectra of thin-film ZnO–LPZT and ZnO–SiO2 structures in the UV and visible spectral regions are presented.
Characteristics of Electromagnetic Wave Absorption in Cylindrical Black Holes with Positive and Negative Refractive Indexes
The problem of plane electromagnetic wave scattering by cylindrical “black holes” with radial profile of dielectric permittivity and magnetic permability in the shell chosen in the form ε(ρ) = μ(ρ) ~ 1/ρ2 and with constant permittivity and permeability in the central region is considered. The problem in rigorous formulation is solved both analytically for a basic model of the absorber and numerically using the one-dimensional method of finite elements for a modified model. The results obtained for absorption efficiency, radar cross-section, and field distribution in the cylinder are presented and discussed. It is shown that the absorption efficiency of the cylinder with negative refractive index at realistic values of parameters of the cylinder remains higher than the absorption efficiency of a similar cylinder with positive refractive index. However the indicated advantage is not so great as the advantage compared to the absorption efficiency of the black body predicted in the previous publications for the case of extremely low losses at the surface of the cylinder and extremely high magnitudes of negative permittivity and permeability and losses in the central region of radius approaching zero.
The Influence of Thermal Treatment and Solar Radiation on the Optical Characteristics of Zinc Oxide Nanostructures
The luminescence properties of ZnO nanorods and nanocrystals after high-temperature annealing in air and exposure to strong solar radiation were studied. Under UV radiation, as-prepared nanorods and nanocrystals exhibit the luminescence spectra with maxima at 380–384 and 560–570 nm. The thermal treatment and high-intensity solar radiation of both nanostructures results in an increase in the intensity of short-wave length luminescence bands. Moreover, the long-wave luminescence band (LB) vanishes in the spectra of nanorods, and a new band at 520 nm appears in the luminescence spectra of nanocrystals. The effect of solar radiation on the properties of nanorods is more pronounced than in the case of nanocrystals, it is possible due to predominately ray heating (annealing) of nanorods than nanocrystals.
Possibilities of Applying Geometric Optics for Calculations of Nano- and Microstructures in Photovoltaic Devices
The optical characteristics used in the photovoltaics of nano- and microstructure, evaluated using electromagnetic radiation transfer computation software, mismatch with data obtained at high estimated times. The ability to apply the geometric optics approximations is shown for this purpose. Relevant computations using a 3D ROKS-RG programming tool (the Monte Carlo method) are performed for various experimental results on the optical parameters of nano- and microstructures available in the scientific literature. Given that surface roughness exists as a byproduct of etching during the preparation of structures, the theory is found to satisfactorily agree with experiment. Moreover, most of the radiation is absorbed on account of the surface roughness of substrates, which is expected to induce a nonuniform charge carrier distribution over the structure height and may be among the reasons for the insufficiently high efficiency of solar elements with radial p–n geometry.
Chlorin e6–CdSe/ZnS Quantum Dots Nanocomposites as Efficient Singlet Oxygen Generator
A new approach to the formation of colloidal nanocomposites based on CdSe/ZnS quantum dots and monomeric form of Chlorin e6 is suggested. We demonstrate that FRET with efficiency close to theoretical prediction can be realized in the nanocomposites, and it leads to twofold enhancement of singlet oxygen generation in comparison with the same amount of free Chlorin e6.
Stability of Optical Responses from Lead-free Perovskite Films
Materials with perovskite-type crystal structure attract much attention due to their unique optical properties, such as high quantum yield of photoluminescence and high carrier mobility. However, their further utilization as an active media in photonic and optoelectronic devices is limited by the lack of stability of their optical responses together with the presence of lead cations in the chemical composition. Here, a detailed study of the optical properties and their stability under ambient conditions of perovskite films with the chemical composition (CH3NH3)xAyIz, where A = Pb, Bi, Sb, was performed. The changes in optical responses of the samples were monitored for 3 months. It was shown that the stability of perovskite films was improved by surface passivation with a thin layer of polymethylmethacrylate onto their surface. The developed procedures of film formation and following surface passivation are of interest in the design of active optical materials based on perovskite films with the increased optical performance.
A Comparative Study of Optical Properties of Thin Films of MPS-encapsulated CdS Quantum Dots and SiO2/MPS-encapsulated CdS Quantum Dots Mixture
The aim of this study is to investigate the optical properties of thin films of MPS-encapsulated CdS quantum dots (QDs) and SiO2/MPS-encapsulated CdS QDs mixture. For this purpose, SiO2 sol and colloidal MPS-encapsulated CdS QDs were mixed and then deposited on a glass substrate by spin coating. Also, the spin coating method was used to deposit the colloid-produced MPS-encapsulated CdS QDs and in this way the QDs were self-assembled onto the glass substrate. The films were heat treated at 150°C under N2 atmosphere. The optical properties of the films were characterized by UV-Vis absorption spectrophotometer and NKD spectrophotometer measurements. The refractive index and thickness of the films were calculated by fitting the measured data in a Drude–Lorentz model. The refractive index values were found 1.90 and 1.51 for the thin films of the MPS-encapsulated CdS QDs and SiO2/QDs mixtures, respectively. According to this result, the refractive index value of the SiO2/CdS QDs mixture thin film is close to the glass substrate and such films may be a good candidate for planar luminous solar concentrators.
Fano Resonant Cuboidal Dielectric Nanoantennas
In this paper, we report Fano resonance in the dielectric disk and rod cuboidal nanoparticles. In these nanoparticles, forward to backward scattering ratio is enhanced as compared to cubic or other symmetrical nanoparticles. Electric and magnetic dipole resonances come closer by tailoring the dimensions of cuboidal nanoparticles so that both of them spectrally overlap and on-resonance scattering of electric and magnetic dipole moments take place in the visible region. Broad electric dipole and narrow magnetic dipole act as bright and dark modes, respectively. Interaction of these modes generate Fano dip in the backward scattering and enhancement in the forward scattering leading to the improvement in directivity and radiation efficiency which can be used for the design of highly directional nanoantennas in the visible region.
Comparison of Characteristics of Waveguide Refractometric Sensors
The operation of three types of waveguide refractometric sensors—interferometric Mach–Zehnder, interferometric two-mode, and grating waveguide—has been analyzed. The design features of these sensors with division into functional blocks have been considered. The overall dimensions of sensors based on chalcogenide glasses have been calculated to obtain the same detection limit for the gas analyzed medium.
An Inverse Numerical Simulation for Simultaneous Measurement of Non Spherical Particle Size and Optical Constant by Forward Elastic Light Scattering and Transmittance
This numerical study investigates the feasibility of simultaneous retrieval of particle size distribution (PSD) and optical constants of spheroids by optical spectroscopy. In this simulation the particles are considered as spheroid. The aspect ratio of an oblate and prolate spheroid is set as 0.8 and 1.2, respectively. At this constant aspect ratio, the particle’s orientation has been changed by altering its major semi-axis. Two continuous wavelength lasers are employed to irradiate the particle samples. Multi-angle and multi-wavelengths elastic forward scattering intensity and the spectral collimated transmittance are employed to measure signals. For forward scattering, the spheroid is effectively replaced by a sphere of an approximated radius and the modified Mie theory is employed to calculate the scattering intensity. For the collimated transmittance, the extinction efficiency of non-spherical particle is measured based on the extended anomalous diffraction approximation. The Log-Normal distribution is used to get the volume frequency distribution of the particles and the inverse process is done by using the improved quantum particle swarm optimization. Two different sets of optical constant (e.g., complex refractive index), semi-major axis of non-spherical particle and discrete rate are retrieved by the inverse simulation. The results show that, the proposed spectroscopic technique can retrieve PSD and optical constants of non-spherical particles simultaneously within the tolerable error limit less than 10%.
Transition Regions in Planar W Optical Fibers
Transition regions at the interfaces of single- and dual-mode regimes have been investigated for some configurations of planar W optical fibers based on numerical solution of the dispersion equation. It is shown that the sizes of the transition regions under consideration at the cutoff frequencies of the fundamental, first odd, and second even modes depend strongly on the geometric and optical parameters of W optical fibers. These circumstances should be taken into account when choosing parameters of W optical fibers in order to ensure in them a stable single-mode or multimode regime, necessary field concentration, and efficient filtering of leaky modes.
Spectral and Kinetic Studies of Photochromic Systems Based on Graphene and Graphene Oxide Nanostructures
A comparative spectral and kinetic study of the reactions of thiol-substituted molecules of diarylethene and spirooxazine with graphene nanoparticles and graphene oxide nanoplates has been performed. Differences in the photochromic transformations of compounds that are in contact with the surface of carbon nanoparticles in relation to the structure of the compounds and the nature of the nanoparticles are revealed, which indicates the chemical and physical interaction of the molecules of photochromic compounds with the surface groups of carbon nanostructures.
Role of Aging in the Formation of Non-spherical Nanostructures during Laser–Matter Interaction in Water
Pulsed laser ablation of different surfaces in liquid environment has broad prospects to selectively synthesize nanoparticles (NPs) with specific optical properties, as well as morphology, size and composition. The dependence of the morphology and particle size on the pulse duration and other external conditions allows synthesizing nano-sized particles for various scientific, particularly, optical, and industrial needs. Most previous studies on ablation of metals in water have shown spherical shapes of NPs without elaboration on the effect of aging on those shapes. In this study, we demonstrate notable modification in the morphology of aluminum, indium, zinc and copper NPs during aging towards the non-spherical structures, contrary to other laser ablation-induced spherical NPs from different elements in the periodic table.
Optical Properties of Spherical Metal Nanoparticles Coated with an Oxide Layer
The optical properties of an ensemble of metal nanoparticles coated with an oxide layer have been investigated within framework of the classical theory. The influence of the electron-scattering mechanisms on the polarizability of nanoparticles is analyzed. The limiting case of a thin oxide layer is considered, and analytical expressions for the real and imaginary parts of the polarizability are derived. The evolution of the frequency dependences of the polarizability and extinction coefficient upon variation in the particle size and oxide-layer thickness is investigated. It is shown that the consideration of the size dependence of the surface component of the relaxation time changes the character of the size dependence of the frequency of surface plasmons of two-layer nanoparticles.
Monitoring of Changes in Oxygen Concentration in Tissues by the Kinetics of Delayed Fluorescence of Exogenous Dyes
The dynamics of the consumption of oxygen during photodynamic processes and the subsequent restoration of its concentration in malignant tumors and healthy tissues of mice were studied in vitro by the kinetics of long-term luminescence of xanthene dyes. To assess changes in the oxygen concentration in tissues, delayed fluorescence can be used due to singlet–triplet annihilation of singlet oxygen and a sensitizer in the triplet state. Upon periodic pulse excitation of sensitizers, reversible quenching of delayed fluorescence was detected in tumors, which is associated with a decrease in the amount of oxygen in the tissues during photodynamic processes. A method for visualizing the restoration of the initial oxygen concentration in tissues is proposed.
Lidar Probing of a Mixture of Hydrogen Sulfide and Methane Molecules in the Atmosphere from a Flying Platform
The results of numerical solution of the lidar equation for the Raman scattering on the molecules of a gas mixture of hydrogen sulfide and methane in the 180° direction when probing the molecules of hydrogen sulfide and methane in the atmospheric boundary layer with concentrations in the range of 1010–1016 cm–3 from a flying platform at altitudes of up to 500 m in the synchronous photon counting mode are presented. It is shown that concentrations of the studied hydrogen sulfide and methane molecules below the level of the maximum permissible concentration (MPC) for such a version of the Raman scattering lidar can be recorded within a measurement time of 10 s when probing at a laser radiation wavelength of 405 nm and a platform flight height in the range of up to 500 m.
Comparative Analysis of the Sensitivity of Optical Sensors Based on Surface Waves Excited in the Kretschmann Scheme
Based on the theory of reflection of a limited light beam from a plane-layered structure, a surface plasmonic wave excited on the free surface of a gold film and, for comparison, a surface wave in a planar surface waveguide, both excited in the Kretschmann scheme, have been examined. The sensitivities of optical sensors based on these surface waves are compared. Various methods are proposed for increasing the sensitivity of sensors based on a surface waveguide. The required fabrication accuracy of film thicknesses to obtain workable sensors is estimated.