Optics and Spectroscopy (v.115, #4)

Possibilities of high-resolution spectroscopy of atoms (or molecules) for optical pumping and probing with the use of a proposed cell with a series of plane-parallel thin gas layers between spatially separated regions of this cell are theoretically studied. It is shown that efficient velocity selection of optically pumped atoms is possible in view of their characteristic transit and collisional relaxation in such a cell, which leads to the formation of narrow sub-Doppler resonances in absorption of a probe monochromatic wave. The resolution of this spectroscopic method is analyzed in the cases of stationary and definite nonstationary optical pumping of atoms by broadband radiation for different geometrical parameters of these cells and pumping intensity. The proposed multilayer gas cell is a compact analog of a large number of parallel atomic (molecular) beams and can be the basis for new high-precision and compact optical frequency standards.

The analyses of possible conformations, molecular structures, vibrational and electronic properties of 2-(methylthio)nicotinic acid molecule, C7H7NO2S, with the synonym 2-(methylsulfanyl)nicotinic acid have been first presented theoretically. At the same time, FT-IR and micro-Raman spectra of 2-(methylthio)nicotinic acid were recorded in the regions 400–4000 cm−1 and 100–4000 cm−1, respectively. In our calculations, the DFTB3LYP method with 6–311G(d, p) basis set was used to have the structural and spectroscopic data about the mentioned molecule in the ground state and the results obtained were compared with experimental values. Furthermore, gauge invariant atomic orbital (GIAO) 1H and 13C NMR chemical shifts in different solvents, UV-vis TD-DFT calculations, the highest occupied molecular orbitals (HOMO-2, HOMO-1, HOMO), lowest unoccupied molecular orbital (LUMO), molecular electrostatic potantial (MEP) surface, atomic charges and thermodynamic properties of molecule have been theoretically verified and simulated at the mentioned level. The energetic behavior of title molecule in different solvent media was investigated by using DFT/B3LYP method with 6–311G(d, p) basis set in terms of integral equation formalism polarizable continuum model (IEFPCM). In addition, the calculated infrared intensities, Raman activities, reduce masses and force constants of the compound under study have been also reported.

The electronic structure of two photosensitizing isotruxene dyes used in Grätzel photoelectro-chemical cells has been investigated by the quantum-chemical methods of the density functional theory (DFT) and Bader’s topological analysis of the electron density. It has been shown that intramolecular interactions in the dye molecules stabilize the planar relative arrangement of isotruxene and cyano-acrylic structural fragments, which provides π-conjugation over the whole molecular backbone. Based on the time-dependent density functional theory (TDDFT) calculations and analysis of the Kohn-Sham orbitals, it has been found that the first vertical electronic transition in the spectra of the isotruxene dyes is a combination of a poorly resolved lπ*-type excitation and a well-resolved π-π* excitation. The π-π* excitation admixture is associated with the asymmetric structure of the isotruxene fragment and contributes significantly to the intensity of the first electronic transition.

We have analyzed intensity distributions in fine structure fluorescence spectra of three all-trans-diphenylpolyenes with number of double bonds n = 1−4 in solutions in n-paraffins at 4.2 K. Modeling of spectra by representing each of the vibronic transitions by a zero-phonon line and a phonon wing with certain parameters (width, Debye-Waller factor) made it possible to determine the relative intensities of vibronic transitions. We have calculated and comparatively analyzed the parameters of intramolecular interactions that form fine structure spectra of stilbene and investigated compounds.

Analysis of bistability in molecular J aggregates under their resonant optical excitation taking into account multiparticle effects by L. A. Nesterov; S. V. Fedorov; N. N. Rosanov; B. N. Levinsky; B. D. Fainberg (499-507).
Using a model of a homogeneous chain of molecules, we have analyzed bistability in resonantly excited J aggregates taking into account three-particle contributions to the exciton-exciton annihilation. These contributions, which have an interference nature, have previously been calculated in a work by B.N. Levinsky, L.A. Nesterov, B.D. Fainberg, and N.N. Rosanov (Opt. Spectrosc. 115 (3), 406 (2013)) in the course of derivation of equations of motion for J aggregates from first principles. Factorization of expectation values that correspond to these contributions leads to a closed system of equations in which not only pair, but also triple, interactions between molecules of the chain are taken into account. Numerical calculations have been performed, and their results have been compared with those obtained in calculations without taking into account three-particle contributions. We have shown that, on the whole, the inclusion of three-particle interference contributions in equations of motion leads to a restriction of the domain of existence of hysteresis. This, in turn, makes it possible to more reliably single out a real range of parameters in which nonlinear optical effects can considerably manifest themselves.

We have studied the fluorescence sensitization and quenching for pairs of different dyes simultaneously incorporated into nanoparticles from complexes M(diketone)3phen, where M(III) is La(III), Lu(III), or Sc(III); diketone is p-phenylbenzoyltrifluoroacetone (PhBTA) or naphthoyltrifluoroacetone (NTA); and phen is 1,10-phenanthroline. We have shown that, upon formation of nanoparticles in the solution in the presence of two dyes the concentrations of which are either comparable with or lower than the concentration of nanoparticles (<20 nM), the intensities of the sensitized fluorescence of dyes in nanoparticles in binary solutions and in solutions of either of the dyes coincide. We have found that the intensity of sensitized fluorescence of small (<20 nM) concentrations of rhodamine 6G (R6G) or Nile blue (NB) increases by an order of magnitude upon simultaneous introduction into nanoparticles of 1 μM of coumarin 30 (C30), while the intensity of fluorescence of C30 sensitized by complexes decreases by an order of magnitude. The same effect is observed as 1 μM of R6G are introduced into nanoparticles with NB ([NB] ≤ 20 nM). The increase in the fluorescence of dye molecules upon their incorporation from the solution into nanoparticles from complexes is noticeably lower than that expected from the proposed ratio of concentrations of complexes and dyes in nanoparticles. Analysis of the obtained data indicates that the introduction of large concentrations of C30 or R6G dyes into nanoparticles makes it possible to prevent large energy losses due to impurities or upon transition to a triplet state that arises during the migration of the excitation energy over S 1 levels of complexes. Energy accumulated by these dyes is efficiently transferred to another dye that is present in the solution at lower concentrations and that has a lower-lying S 1 level, which makes it possible to increase its fluorescence by an order of magnitude upon its incorporation into nanoparticles.

Cyclometalated [M(C∧N)En]PF6 (M = Pd(II), Pt(II)) and [M(C∧N)2En]PF6 (M = Rh(III), Ir(III)) complexes ((C∧N) corresponds to the deprotonated forms of 2-tolylpyridine and benzo[h]quinoline, and En is ethylenediamine) are studied by 1H NMR spectroscopy, electronic absorption and emission spectroscopy, and voltammetry. Metalation of heterocyclic ligands leads to the formation of five-membered {M(C∧N)} cycles in the composition of square planar and octahedral complexes of the cis-C,C structure. Correlation of the energy positions of the long-wavelength metal-to-ligand charge-transfer absorption bands with the difference between the potentials of one-electron waves of metal-centered oxidation and ligand-centered reduction of complexes is shown. The phosphorescence of the complexes in the visible region of 469–524 nm is attributed to the radiative transition from the metal-modified intraligand excited state. The temperature quenching of the phosphorescence of complexes is attributed to the thermally activated population of metal-centered electronically excited states with subsequent nonradiative deactivation.

Investigation of optical homogeneity and photorefractive properties of lithium-niobate single crystals by the Raman-spectroscopy and laser-conoscopy methods by N. V. Sidorov; M. N. Palatnikov; A. A. Yanichev; A. A. Gabain; O. Yu. Pikoul; A. N. Smirnov (523-529).
Photorefractive properties and structural and optical homogeneity of (1) LiNbO3:Cu crystals ([Cu] = 0.015 mas %) grown from a congruent melt, (2) nominally pure stoichiometric crystals grown from a melt with 58.6 mol % of Li2O (LiNbO3stoich), and (3) nominally pure congruent crystals (LiNbO3congr) have been studied using the Raman-spectroscopy method with excitation in the UV, visible, and near-IR ranges; the laser-conoscopy method; and the electron paramagnetic resonance-spectroscopy method. In optically uniaxial LiNbO3 crystals, a weak optical biaxiality has been revealed, which is attributed to an insignificant deformation of the optical indicatrix. This deformation can be caused both by the initial structural inhomogeneity of crystals and by the photorefractive effect. It has been shown that, under the action of light, charge exchange of copper cations Cu2+ → Cu+ takes place in the crystal LiNbO3:Cu ([Cu] = 0.015 mas %). The LiNbO3:Cu crystal exhibits photorefractive properties not only because of the occurrence of intrinsic defects with electrons localized at them, as is the case with the LiNbO3stoich and LiNbO3congr crystals, but also due to the charge exchange of copper cations under the action of the laser radiation.

A fluorescence spectroscopy study of traditional Chinese medicine Angelica by Hongyan Zhao; Feng Song; Shujing Liu; Guiyang Chen; Chen Wei; Yanling Liu; Jiadong Liu (530-536).
By measuring the fluorescence spectra of Chinese medicine (CM) Angelica water solutions with different concentrations from 0.025 to 2.5 mg/mL, results showed that the fluorescence intensity was proportional to the concentration. Through fluorescence spectra of Angelica solution under different pH values, results indicated coumarin compounds were the active ingredients of Angelica. We also observed fluorescence quenching of the Angelica solution in the presence of spherical silver nanoparticles with radius of 12 nm. Keeping a certain value for the volume of the silver nanoparticles, the fluorescence intensity at 402 nm was linearly proportional to the Angelica in the range of 1–3 mg/mL.

Analysis and applications of phase shifts for multichannel fiber Bragg grating by Guodan Sun; Rong Wang; Tao Pu; Zhihu Wei; Jintian Xiong; Hui Li (537-543).
A novel phase compensation method to improve comb filters performance by increasing DC refractive index of linearly chirped fiber Bragg grating (LCFBG) is proposed. Nonlinear chirp introduced by linearly chirped mask is discussed, and then DC phase shift compensate method is proposed. Two kinds of DC phase shift LCFBGs are analyzed, which shows a good agreement with traditional discrete phase shift method. A DC phase shift comb filter is realized with the help of a micrometer-precision translation stage, which shows the feasibility to introduce DC phase shift in LCFBG. A high flattened comb filter with precise 0.8 nm channel spacing is realized with the help of a micrometer precision translation stage.

Kerr nonlinearity and EIT in a double Lambda type atomic system by Hamid Reza Hamedi; Ali Khaledi-Nasab; Ali Raheli (544-551).
The giant Kerr nonlinearity in a four-level double Lambda type atomic system is theoretically predicted. We find that an enhanced Kerr nonlinearity can be achieved just by the intensity of coupling filed that lies within the transparency window. It is also shown that the giant Kerr nonlinearity with reduced absorption can be achieved by the quantum interference mechanisms.

Pressure changes of isotropic points in potassium-sulfate crystals by V. I. Stadnyk; N. A. Romanjuk; B. V. Andriyevsky; R. S. Brezvin; O. Z. Kashuba (552-556).
The influence of uniaxial pressures applied along the principal crystallographic directions on the dispersion and temperature dependences of the birefringence of potassium-sulfate crystals K2SO4 has been investigated. It has been found that the birefringence is quite sensitive to uniaxial pressures. The behavior of isotropic points has been analyzed, and temperature-spectral-baric diagrams of the isotropic state of the K2SO4 crystals have been constructed.

The possibility of using commercial digital cameras that support image saving in the RAW format in scientific applications for measuring spatial intensity distributions in different ranges of the visible spectrum is considered. Spectral characteristics of photo sensors were measured for three digital cameras: Canon EOS 1000D, Nikon D50, and Nikon D90. Ways of applying spectral characteristics in problems of improving the quality of multicolor digital holograms are considered.

A miniature prototype of a resonance photoacoustic cell for gas sensing by A. V. Gorelik; A. L. Ulasevich; A. A. Kuz’muk; V. S. Starovoitov (567-573).
We present a miniature prototype of a resonance photoacoustic cell with a banana-shaped internal cavity with a volume of less than ∼5 mm3. The cell design and the experimental setup used for testing operational characteristics of the prototype are described. The results of testing the prototype in the experiments on photoacoustic detection of radiation absorption by ammonia in a nitrogen flow by using a single-mode diode laser generating radiation near ∼1.53 μm are presented. The amplitude-frequency characteristic of the photoacoustic response induced by absorption of radiation in the presence and absence of ammonia is analyzed. The experiment revealed that sensitivity of gas sensing is limited only by the microphone noise. The measured noise-limited minimal detectable absorption was found to be about 8.48 × 10−8 cm−1 W Hz−1/2.

The existence as well as concentration of light (low-atomic number) elements is directly related to some of the most important properties of almost all materials. Thus, the development of a direct, fast, and sensitive spectroscopic method for the analytical quantification of these elements is considered an important continuing challenge in many fields. In this report, results obtained from previous as well as most recent studies regarding trace detection of light elements in non-conducting materials by laser-induced breakdown spectroscopy (LIBS) technique are reviewed for the first time. Firstly, we introduce investigations performed in the far- and vacuum-UV as well as UV-visible-NIR spectral domains, and cover many non-conducting materials including gases, aerosols, soil, cement, and selected organic compounds. The report also demonstrates important analytical results for the elements lithium, beryllium, boron, carbon, fluorine, phosphorus, sulfur, and chlorine. In addition, key characterization information relating to a specific element in a given matrix and state is summarized in such a way that relevant resources can easily be traced. Furthermore, in order to facilitate tracking down the evolution of the technique for a particular material category, a chronological order has been devised. In the second part of the review, the latest developments and advances in instrumentation and methodologies of the LIBS technique, particularly in the realm of light elements detection, are discussed. The sensitive detection of light elements in the UV-VIS-NIR is still unsatisfactory, and more work is needed in order to achieve better analytical performance in terms of precision, accuracy and limits of detection. The author anticipates that significant sensitivity improvements should be realized by combining LIBS, employing femtosecond laser pulses, with other diagnostic techniques based on probing the plasma via diode lasers.

The interaction of laser radiation with an axially symmetric polarization with condensed media is studied theoretically. The interaction results in the formation of ordered micro- and nanoscale structures that can be described in terms of the universal polariton model of laser-induced media damage. It is shown that the radially polarized radiation induces a periodic ring resonance grating that focuses the excited surface plasmon-polaritons, thus increasing the total light intensity in the center of the irradiated zone.

CdTe quantum dots as fluorescence sensor for the determination of aminophylline in aqueous solution by Rui-yong Wang; Jing Wu; Lv-jing Wang; Rui Wang; Huan-jing Dou (596-600).
A novel CdTe quantum dots (QDs) based technology platform was established in aqueous solution. It can perform accurate and simple determination of aminophylline concentration in pharmaceutical samples with satisfactory results. Under optimum conditions, the relative fluorescence intensity of CdTe quantum dots is linearly proportional aminophylline concentration from 2.00 to 80.0 μg mL−1 with a correlation coefficient of 0.9979 for aminophylline determination and a detection limit of 0.531 μg mL−1.

Complex polarization-phase and spatial-frequency selections of laser images of blood-plasma films in diagnostics of changes in their polycrystalline structure by Yu. A. Ushenko; P. O. Angelskii; A. V. Dubolazov; A. O. Karachevtsev; M. I. Sidor; O. P. Mintser; B. P. Oleinichenko; L. I. Bizer (601-609).
We present a theoretical formalism of correlation phase analysis of laser images of human blood plasma with spatial-frequency selection of manifestations of mechanisms of linear and circular birefringence of albumin and globulin polycrystalline networks. Comparative results of the measurement of coordinate distributions of the correlation parameter—the modulus of the degree of local correlation of amplitudes—of laser images of blood plasma taken from patients of three groups—healthy patients (donors), rheumatoid-arthritis patients, and breast-cancer patients—are presented. We investigate values and ranges of change of statistical (the first to fourth statistical moments), correlation (excess of autocorrelation functions), and fractal (slopes of approximating curves and dispersion of extrema of logarithmic dependences of power spectra) parameters of coordinate distributions of the degree of local correlation of amplitudes. Objective criteria for diagnostics of occurrence and differentiation of inflammatory and oncological states are determined.

A method for operative retrieval of spatial distributions of biophysical parameters of a biological tissue by using a multispectral image of it has been developed. The method is based on multiple regressions between linearly independent components of the diffuse reflection spectrum of the tissue and unknown parameters. Possibilities of the method are illustrated by an example of determining biophysical parameters of the skin (concentrations of melanin, hemoglobin and bilirubin, blood oxygenation, and scattering coefficient of the tissue). Examples of quantitative interpretation of the experimental data are presented.

A simple example is used to demonstrate that, during the calculation of tolerance for prism angles, one should pay attention to their application conditions and to the mutual influence of primary errors, which has not been described in the literature. We propose a simple vector-matrix method as one of the possible solutions to the problem of error determination in mirror-prism systems and the specification of tolerances. Statistical analysis of tolerances for the AP-90 prism demonstrates the efficiency of the method.