Showing papers in "Optics and Spectroscopy in 2000"
TL;DR: In this article, the dynamics of the changes in the statistical polarization structure of coherent images of biological tissues are studied for the visualization process of their optically anisotropic (collagen) structure.
Abstract: The dynamics of the changes in the statistical polarization structure of coherent images of biological tissues are studied for the visualization process of their optically anisotropic (collagen) structure.
87 citations
TL;DR: In this paper, the possibility of using laser polarization techniques to diagnose the appearance and development of pathological changes in the morphological structure of biotissues is analyzed, and the results show that laser polarization can be used to diagnose pathological changes.
Abstract: The possibility of using laser polarization techniques to diagnose the appearance and development of pathological changes in the morphological structure of biotissues is analyzed.
74 citations
TL;DR: In this paper, the scattering of laser radiation by structured biotissues, such as bony and muscular tissues and skin, was studied, and the effect of the laser radiation on these structures was investigated.
Abstract: Scattering of laser radiation by structured biotissues—histological mounts of bony and muscular tissues and skin, are studied.
74 citations
TL;DR: In this article, the formation of a fine polarization structure of biospeckles of derma is studied, and a method for phase compensation of the degree of depolarization is proposed, which makes possible a severalfold increase of the measurement sensitivity.
Abstract: 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.
69 citations
TL;DR: In this paper, the stationary and time-resolved photoluminescence spectra of n-pentyl-n′-cyanobiphenyl (5CB) were studied in a mesophase and solid-crystal state.
Abstract: The stationary and time-resolved photoluminescence spectra of n-pentyl-n′-cyanobiphenyl (5CB) are studied in a mesophase and solid-crystal state. The photoluminescence spectra of 5CB are determined by the molecular configuration and the intramolecular charge transfer in the excited state. It is shown that in the mesophase and solid-crystal state, 5CB exhibits along with monomer radiation at least two types of excimer radiation from different pre-dimer states.
63 citations
TL;DR: In this article, the reflection and transmission of light by cholesteric liquid crystal-glass-cholesteric laminar liquid crystal (CLFL) systems were studied using the classical Ambartsumyan method and the concept of sewing function.
Abstract: Reflection and transmission of light by cholesteric liquid crystal-glass-cholesteric liquid crystal and cholesteric liquid crystal(1)-cholesteric liquid crystal(2) systems were studied. The classical Ambartsumyan method of adding layers and the concept of a sewing function were used. This approach was developed earlier in astrophysics for the theory of radiation transfer. Here, we used a version of this method adapted to wave optics. The Jones matrices are constructed for these systems. The features of the reflection and transmission spectra, optical rotation and ellipticity of polarization were studied for these systems. It is proposed to use these systems as tunable narrow-band filters and mirrors. These systems can be used, for example, to develop a variety of optical elements for lasers and of polarimetric elements in ellipsometry. The specific features of eigenpolarization are also discussed. It is shown that optical rotation of the two layers of cholesteric liquid crystals, which differ from each other only by the sign of the helix, is nonzero, and it becomes substantial in the diffraction reflection region. A unique property of these systems is the degeneracy (coincidence) of eigenpolarizations.
48 citations
TL;DR: In this paper, the absorption spectra of a series of solutions of C60 and C70 and of their mixture in o-xylene were studied, and the deviation from the Bouguer-Lambert-Beer law was observed in the UV absorption band of the solutions.
Abstract: The absorption spectra of a series of solutions of C60 and C70 and of their mixture in o-xylene are studied. The deviation from the Bouguer-Lambert-Beer law was observed in the UV absorption band of the solutions. The possible reasons for this effect were analyzed. It is shown that to calculate reliably the composition and concentrations of fullerene mixtures, it is necessary to determine preliminarily the linearity region for the 335-nm absorption band.
43 citations
TL;DR: In this article, the properties of dissipation of the excitation energy in garnet crystal phosphors with rare-earth ions with interconfiguration transitions were studied depending on the Ga concentration.
Abstract: Mechanisms of dissipation of the excitation energy in garnet crystal phosphors Y3Al5O12 and Y3Ga5O12 doped with rare-earth ions with interconfiguration transitions are studied depending on the Ga concentration.
36 citations
TL;DR: In this article, the authors considered the non-resonant case of the Jaynes-Cummings model without rotating-wave approximation, and the analysis was carried out using the resolvent formalism.
Abstract: 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.
35 citations
TL;DR: In this paper, the transmission and reflection of light normally incident on a layer of a medium with dielectric and magnetic helicities is studied and the Jones matrices are constructed.
Abstract: 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.
34 citations
TL;DR: In this paper, an analysis of the light field structure in the vicinity of a line of the ring phase dislocation corresponding to the zero value of the field formed by the interference of two uniaxial Gaussian beams is made.
Abstract: In the scalar approximation, an analysis is made of the light field structure in the vicinity of a line of the ring phase dislocation corresponding to the zero value of the field formed by the interference of two uniaxial Gaussian beams. The formation of an “optical vortex” or the toroidal motion of a portion of a light flow around a ring phase dislocation is shown.
TL;DR: In this article, a problem of light scattering by multilayer confocal ellipsoids is solved in the Rayleigh approximation, where the electric field of a light wave is assumed constant and a set of Laplace equations with the corresponding boundary conditions is considered.
Abstract: A problem of light scattering by multilayer confocal ellipsoids is solved in the Rayleigh approximation. The electric field of a light wave is assumed constant and a set of Laplace equations with the corresponding boundary conditions is considered. The final expression for the polarizability of a particle is represented in the matrix form (2×2 matrices) in terms of parameters of a nucleus and subsequent layers. Numerical calculations of the scattering and absorption efficiencies of small multilayer spheres obtained using the exact (the generalization of the Mie theory) and approximate solutions well agree with each other.
TL;DR: The existence of a metastable topological (with a wave front dislocation and an annular intensity distribution) three-dimensional dissipative optical soliton is demonstrated in this paper.
Abstract: 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.
TL;DR: In this article, the emission spectra of a gas-discharge plasma produced in a HgBr/HgCl excimer lamp, which was filled with multicomponent working mixtures at atmospheric pressure (HgBr2 and HgCl2 with additions of molecular nitrogen and xenon), are reported.
Abstract: A study of emission spectra of a gas-discharge plasma produced in a HgBr/HgCl excimer lamp, which is filled with multicomponent working mixtures at atmospheric pressure (HgBr2 and HgCl2 with additions of molecular nitrogen and xenon), are reported. A gas-discharge plasma was produced by high-frequency (pulses ∼100 ns long with a repetition rate of up to 2000 Hz) barrier and surface discharges, which took place simultaneously. Emission of HgBr* and HgCl* excimer molecules, the second positive system of molecular oxygen, and helium and xenon lines in the UV, visible, and IR spectral regions was observed. The strongest emission of HgBr* and HgCl* molecules (the emission intensities were in the ratio 10:1) was observed in the HgBr2: HgCl2: N2: He mixture. Regularities in spectral and integrated characteristics of gas-discharge plasma emission are discussed.
TL;DR: In this paper, an analysis is made of single-mode fiber optical waveguides with linear birefringence and regular twist of anisotropy axes in the presence of random twist, which shows that the coupling of orthogonal polarization modes having elliptic polarization in the screw coordinate system comoving with twist cannot be characterized by one coupling parameter.
Abstract: An analysis is made of single-mode fiber optical waveguides with linear birefringence and regular twist of anisotropy axes in the presence of random twist, which shows that, in this case, the coupling of orthogonal polarization modes having elliptic polarization in the screw coordinate system comoving with twist cannot be characterized by one coupling parameter, as differentiated from the case where constant twist is absent. In this case, the coupling between polarization modes is characterized by three independent parameters, which are different in nature and have different effects on the coupling of polarization modes. An estimate is made of the domain of applicability of the classical formula for the h parameter in single-mode fiber optical waveguides without regular twist of anisotropy axes.
TL;DR: In this article, the authors developed a microscopic theory of a transitional layer on the ideal surface of a semi-infinite absorbing or nonabsorbing isotropic dielectric when the polarization vector of the medium is a linear function of the electric field strength inside the medium.
Abstract: The microscopic theory of a transitional layer on the ideal surface of a semi-infinite absorbing or nonabsorbing isotropic dielectric is developed within the framework of classical optics when the polarization vector of the medium is a linear function of the electric field strength inside the medium. The concentration of atoms (molecules) of the medium and their polarizability are independent of coordinates and are constant inside the medium and close to its surface. The consideration is carried out within the framework of the concept of a discrete-continuous dielectric, in which the fields of dipoles of discretely distributed atoms (molecules) inside the Lorentz sphere surrounding the observation point are taken into account. The near-field effect is shown to result in a nonexponential behavior of the field nearby the surface. The thickness of the transitional layer can be found from experimental values of the reflected wave amplitude.
TL;DR: In this article, conditions for the existence of completely localized three-dimensional dissipative laser solitons in a medium with nonlinear amplification and absorption and frequency dispersion are studied.
Abstract: Conditions for the existence of completely localized three-dimensional dissipative laser solitons—“laser bullets” in a medium with nonlinear amplification and absorption and frequency dispersion are studied. Solitons with different profiles are considered and the regions of their stable existence are found. The stability of spherical solitons is studied as a function of frequency mismatch of amplification and absorption lines by the method of direct numerical simulation.
TL;DR: The lateral shift of a light beam reflected from the interface between an optically transparent dielectric and a medium for which the frequency dependences of the real and imaginary parts of the permittivity have a resonant form is investigated in this paper.
Abstract: The lateral shift of a light beam reflected from the interface between an optically transparent dielectric and a medium for which the frequency dependences of the real and imaginary parts of the permittivity have a resonant form is investigated. At certain radiation frequencies and angles of incidence, a negative displacement of the reflected beam along the interface takes place.
TL;DR: In this article, the excited states and absorption and fluorescence spectra of styrene and β-d 2-styrene are calculated by the parametric method, which is shown to adequately describe their real structure and predict the fine structure of their electronic spectra at the quantitative level.
Abstract: The excited states and absorption and fluorescence spectra of styrene and β-d 2-styrene are calculated by the parametric method. It is shown that parametric models of these molecules in the excited states adequately describe their real structure and predict the fine structure of their electronic spectra at the quantitative level, which is sufficient for its detailed interpretation and the refinement of parameters of the molecular model by solving inverse problems. In a second approximation (using only one additional parameter), the method provides a more exact calculation of angular deformations of the molecule upon excitation and, in particular, describes characteristic differences in the intensities of low-frequency spectral components in a series of diphenylpolyene-stilbene-styrene. The number of parameters for molecular fragments is small (2 and 3 in the first and second approximations, respectively), and they are the same for a series of related compounds. Compared to direct ab initio calculations, the parametric method yields substantially better results already in the first approximation, and it is more efficient for modeling molecules in excited states and description of their vibronic spectra.
TL;DR: In this article, the CsPbX3 (X=Cl, Br) microcrystals were obtained in a PbX2 matrix doped with Cs ions (CCs=0.1-1 mol %).
Abstract: The CsPbX3 (X=Cl, Br) microcrystals are obtained in a PbX2 (X=Cl, Br) matrix doped with Cs ions (CCs=0.1–1 mol %). Spectral and kinetic parameters of the intrinsic luminescence of the CsPbX3 single crystals are presented. For the CsPbCl3 microcrystals, a quantum-confinement effect is detected, which reveals itself as a decrease in the lifetime of the free exciton luminescence. A mechanism of formation of a CsPbX3 microcrystal in a PbX2 matrix is proposed.
TL;DR: In this paper, the temperature dependence of the mean polarizability of the H2, N2, and O2 molecules is calculated in the temperature range up to 2000 K. The temperature dependence is represented in the form of a second degree polynomial.
Abstract: The temperature dependence of the mean polarizability of the H2, N2, and O2 molecules are calculated in the temperature range up to 2000 K. The values of polarizability derivatives of these molecules from the literature are used in the calculation. The temperature dependence of the mean polarizability of molecules is represented in the form of a second degree polynomial.
TL;DR: In this article, the efficiency of uniform spheroids in the quasi-static approximation and the region of their applicability were studied for the prolate and oblate nonabsorbing particles with refractive indices 1.1≤n≤10 and axial ratios 1. 1≤a/b/b≤100.
Abstract: Expressions are obtained for the efficiency of absorption and scattering of radiation by uniform spheroids in the quasi-static approximation and the region of their applicability is studied. The prolate and oblate nonabsorbing particles with refractive indices 1.1≤n≤10 and axial ratios 1.1≤a/b≤100 were studied. The approximation expressions are found for the particle size at which the efficiency factors are calculated in the quasi-static approximation with an accuracy of 1%.
TL;DR: In this paper, the influence of anions on nonradiative electronic energy transfer between lanthanide ions in aqueous solutions is studied, and it is shown that the energy transfer rate can increase by three orders of magnitude upon addition of salts of hydrofluoric acid to the solution.
Abstract: The influence of anions on nonradiative electronic energy transfer between lanthanide ions in aqueous solutions is studied. The rate constant k t of energy transfer was found to increase by three orders of magnitude upon addition of salts of hydrofluoric acid to the solution. This effect is caused by the formation of bridge labile binuclear complexes, an excited energy donor-fluorine anion-acceptor, which increase the encounter time between a donor and an acceptor, resulting in the increase in the probability of energy transfer. The independence of k t of the Forster overlap integral in the bridge complex containing F− was explained by the fact that energy transfer occurs in each event of the binuclear complex formation, the maximum rate constant of energy transfer being equal to the rate constant of the binuclear complex association. Bridge complexes formed via the NO 3 − anion are also considered. These binuclear complexes are unstable, and k t for them is proportional to the Forster overlap integral. In this case, energy transfer occurs not during each event of the complex formation. This allows us to estimate the lower limit of the dissociation constant of the binuclear complex and its stability constant. Thus, the study of influence of various anions on energy transfer represents a new efficient luminescent method for analysis of properties of labile binuclear complexes in solutions.
TL;DR: In this article, a detailed study of statistical characteristics of photon trajectories in a strongly scattering medium near an object surface is presented, and the properties found in the study may be useful for developing an algorithm of reconstruction in real time for the optical tomography of strongly scattering (biological) object.
Abstract: Results of a detailed study of statistical characteristics of photon trajectories in a strongly scattering medium near an object surface are presented. The properties found in the study may be useful for developing an algorithm of reconstruction in real time for the optical tomography of strongly scattering (biological) object.
TL;DR: In this article, the propagation of laser radiation and fluorescence excited by it in a strongly scattering medium is analyzed in the diffusion equation approximation, and the possibility of applying efficient algorithms of the tomographic reconstruction with the use of mean paths of photons in biotissues to fluorescence laser tomography is substantiated.
Abstract: The propagation of laser radiation and fluorescence excited by it in a strongly scattering medium are analyzed in the diffusion equation approximation. The possibility of applying efficient algorithms of the tomographic reconstruction with the use of mean paths of photons in biotissues to fluorescence laser tomography is substantiated.
TL;DR: In this article, the authors consider the possi- bilities of controlling dispersion properties and transmission spectra of hybrid optical components consisting of photonic band-gap structures filled with a resonant gas.
Abstract: Using the model of an infinite one-dimensional periodic layered structure, we consider the possi- bilities of controlling dispersion properties and transmission spectra of hybrid optical components consisting of photonic band-gap structures filled with a resonant gas. It is shown that the combination of resonance- enhanced gas dispersion with the dispersion of a photonic band-gap structure may give rise to new features in the dispersion and transmission of hybrid spectral elements. These effects can be employed to create narrow- band filters and ultrarefractive prisms with controllable parameters. © 2000 MAIK "Nauka/Interperiodica".
TL;DR: In this article, the amplitude gratings were transformed into phase gratings by irradiation by pulses of incoherent light in the regime of local melting, and a noticeable increase in the diffraction efficiency was found in this case.
Abstract: New methods for the formation of measuring periodic diffraction structures at silicon surfaces are proposed and tested. The one-dimensional grating is formed at a surface of implanted silicon by nanosecond laser annealing in the regime of interference of two crossed beams. The two-dimensional grating is formed at the surface of single-crystal silicon by implantation through a special periodic mask. Diffraction gratings formed are amplitude gratings because their periodically alternating fragments differ only in the reflection coefficient. The amplitude gratings were transformed into phase gratings by irradiation by pulses of incoherent light in the regime of local melting. A noticeable increase in the diffraction efficiency is found in this case, which allows these gratings to be used to study the dynamics of various phase transitions induced by high-power incoherent light pulses in implanted silicon.
TL;DR: In this article, a simulation of the shading effect in systems of opaque spherical particles scattering light in accordance with the Lambert law is presented, and two types of systems are studied: a semi-infinite medium and statistically uniform clusters of a finite number of particles.
Abstract: Results of computer simulation of the shading effect in systems of opaque spherical particles scattering light in accordance with the Lambert law are presented Two types of systems are studied: a semi-infinite medium and statistically uniform clusters of a finite number of particles The simulation makes it possible to obtain photometric characteristics of systems with an accuracy better than 1% The phase dependence of the shading effect is shown to become steeper as the packing density of particles in clusters decreases and their number increases For statistically uniform media, the following relation takes place: The lower the packing density, the more pronounced the shadow decrease in brightness with an increasing phase angle
TL;DR: A phase binary ring diffraction optical element (DOE) with a radius of 3.5 mm and microrelief height of 1.06 μm was calculated and fabricated in this paper.
Abstract: A phase binary ring diffraction optical element (DOE) with a radius of 3.5 mm and microrelief height of 1.06 μm was calculated and fabricated. The element focuses a Gaussian beam of a He-Ne laser with radius of 1.5 mm to a 1.7 mm long axial segment, which ranges from 51.9 to 53.6 mm, with a focal spot diameter of about 30 μm.