Showing papers in "Optics and Spectroscopy in 2012"

Mueller-matrix diagnostics of optical properties of polycrystalline networks of human blood plasma

Abstract: The work is oriented toward a study of the possibilities of Mueller-matrix diagnostics of optical anisotropy of birefringent polycrystalline networks of human plasma amino acids. The interrelations between the statistical moments from the first to the fourth orders and fractal dimensionalities, which characterize the coordinate distributions of elements of the Mueller matrix for the blood plasma and the physiological state of the human organism, are determined.

Wavelet-analysis of polarization maps of human blood plasma

Abstract: Possibilities of local wavelet-analysis of coordinate distributions of polarization azimuths and ellipticity of laser images of blood plasma in healthy and cancer patients are considered. The set of statistical, correlation, and fractal parameters of distributions of wavelet-coefficients characterizing different scales of geometric dimensions of amino acid polycrystalline networks is determined. The criteria for the differentiation of transformation processes of birefringence of optically anisotropic structures of blood plasma at different scales are established.

Exciton absorption spectrum of thin CsPbI3 and Cs4PbI6 films

Abstract: A method for preparing thin films of CsPbI3 and Cs4PbI6 complex compounds has been developed. Their absorption spectrum is investigated in the energy range of 2–6 eV at temperatures from 90 to 500 K. It is found that the CsPbI3 compound is unstable and passes to the Cs4PbI6 phase upon heating at T ≥ 400 K.

Superluminal motion (review)

Abstract: Prior to the development of Special Relativity, no restrictions were imposed on the velocity of the motion of particles and material bodies, as well as on energy transfer and signal propagation. At the end of the 19th century and the beginning of the 20th century, it was shown that a charge that moves at a velocity faster than the speed of light in an optical medium, in particular, in vacuum, gives rise to impact radiation, which later was termed the Vavilov-Cherenkov radiation. Shortly after the development of Special Relativity, some researchers considered the possibility of superluminal motion. In 1923, the Soviet physicist L.Ya. Strum suggested the existence of tachyons, which, however, have not been discovered yet. Superluminal motions can occur only for images, e.g., for so-called “light spots,” which were considered in 1972 by V.L. Ginzburg and B.M. Bolotovskii. These spots can move with a superluminal phase velocity but are incapable of transferring energy and information. Nevertheless, these light spots may induce quite real generation of microwave radiation in closed waveguides and create the Vavilov-Cherenkov radiation in vacuum. In this work, we consider various paradoxes, illusions, and artifacts associated with superluminal motion.

Elemental analysis of fertilizer using laser induced breakdown spectroscopy

Abstract: In recent years, the use of fertilizers has increased to achieve high growth rate of agriculture products. With this increase the chemical impact of agricultural activities on the environment has also been enhanced. In order to keep the environment healthy, and clean, it is necessary to identify contaminants and characterize the sources of contamination. In this study, a comprehensive chemical characterization of a DAP fertilizer has been carried out using laser induced breakdown spectroscopy. Phosphorous, manganese, magnesium, iron, titanium, molybdenum, nickel, cobalt, aluminum, chromium, lead, and uranium traces are detected. Relative abundances of Phosphorous, manganese, magnesium, molybdenum, iron, titanium, nickel, vanadium, calcium, cobalt, cadmium, tin are 26.64, 17.75, 13 97, 8.25, 7.97, 7.11, 5.07, 3.15, 2.94, 1.94, 1,55, 1.73 percent, respectively, whereas relative abundances of sulfur, aluminum, chromium, lead, and uranium are less than 1% and their sum is 1.93% of the total sample.

Structure and spectral properties of truxene dye S5

Abstract: On the ground of functional theory with the B3LYP and BMK functionals, we have studied the structure and optical properties of a truxene dye sensitizer S5 for photoelectric transducers. Based on the calculations of the vertical excitations energy of the dye molecule and accounting the influence of the solvent, we have revealed a positive solvatochromic effect that is weak compared to results obtained in the vacuum approximation. We have studied new features describing stabilization of the planar structure of the cyanothiophene-acrylic fragment of the S5 dye.

Excited states and absorption spectra of β-diketonate complexes of boron difluoride with aromatic substituents

Abstract: In the approximation of the time-dependent electron density functional theory, we have studied using the quantum-chemical method the nature of excited states of boron difluoride acetylacetonate F2BAA and its substituted derivatives that contain aromatic groups with one or two benzene cycles in the β-position. Optimization of the geometry of complexes show coplanar positions of cycles for all compounds, except for that with the substituent C6H3(CH3)2. Based on the calculated transition energies and oscillator strengths, we have simulated the absorption spectra in the prevacuum range. The calculated absorption spectra have been compared with the experimental spectra in the gas phase or in solutions. We show that, in the absorption spectra of complexes that contain substituents with one benzene cycle, the first three bands are caused by the transition of π electrons of the substituent to the LUMO of the chelate cycle. In complexes with two cycles in the substituent, the number of these transitions increases to five. As the π system becomes more extended, a bathochromic shift of the first absorption band and an increase in the transition probability are observed.

Water stress assessment of cork oak leaves and maritime pine needles based on LIF spectra

Abstract: The aim of the present work was to develop a method for the remote assessment of the impact of fire and drought stress on Mediterranean forest species such as the cork oak (Quercus suber) and maritime pine (Pinus pinaster). The proposed method is based on laser induced fluorescence (LIF): chlorophyll fluorescence is remotely excited by frequency-doubled YAG:Nd laser radiation pulses and collected and analyzed using a telescope and a gated high sensitivity spectrometer. The plant health criterion used is based on the I 685/I 740 ratio value, calculated from the fluorescence spectra. The method was benchmarked by comparing the results achieved with those obtained by conventional, continuous excitation fluorometric method and water loss gravimetric measurements. The results obtained with both methods show a strong correlation between them and with the weight-loss measurements, showing that the proposed method is suitable for fire and drought impact assessment on these two species.

Measurement of the luminescence decay times of PbS quantum dots in the near-IR spectral range

Abstract: Methods for recording luminescence decay times of semiconductor PbS quantum dots (QDs) with optical transitions in the near-IR spectral range have been analyzed. A measuring complex for spectral and kinetic analysis in the near-IR range (0.8–2.0 μm) in the time interval from several tens of nanoseconds to several tens of microseconds is described. In this complex, a semiconductor picosecond laser is used as an excitation source; luminescence decay times are recorded by a fast InGaAs photodiode, a high-speed amplifier, and a high-frequency oscilloscope; and the measurement results are multiply averaged (up to a million times) by a program. The technical features of this method are discussed and compared with the characteristics of techniques based on photon counting or application of more powerful radiation sources, and the limitations on sensitivity are analyzed. The results of measuring the luminescence decay kinetics of PbS QDs 2.7–7.6 nm in size prepared in the form of solutions and incorporated into matrices are reported.

The effect of halogen substitution on the structure and electronic spectra of fluorone dyes

Abstract: By means of the B3LYP density functional method with the use of the polarized continuum model PCM, we have performed quantum-chemical computations of the electronic absorption and fluorescence spectra of fluorone dianions: fluorescein, dibromofluorescein, eosin, erythrosine, and Rose Bengal in vacuum and methanol. We have revealed conformational features of the structure of fluorone dianions (charge redistribution, changes in the bond lengths and angles between bonds) second by the halogen substitution, the transition from the ground state to an excited state, and the change of the solvent (vacuum-methanol). Absorption and fluorescence wavelengths, constant dipole moments, transition dipole moments, and oscillator strengths have been calculated. We have showed that, upon halogenation of fluorones, the absorption spectra are redshifted and the Stokes shift decreases, which is qualitatively consistent with experimental results.

Amplification of frequency-modulated soliton-like pulses in inhomogeneous optical waveguides with normal dispersion

Abstract: The possibility of effective amplification of self-similar frequency-modulated pulses (FMPs) in longitudinally inhomogeneous active optical waveguides is studied. Peculiarities of the dynamics of parabolic pulses with a constant frequency modulation rate are considered. An optimal profile of variation of the group velocity dispersion was obtained in correspondence with optimal amplification of a similariton-like pulse. The use of FMPs in amplifying and longitudinally inhomogeneous optical waveguides with a correspondingly matched profile of normal dispersion of group velocities is shown to be capable of providing for an amplification of subpicosecond pulses up to energies above 1 nJ.

FTIR spectroscopic and quantum chemical studies on hydantoin

Abstract: In this study the geometry optimization of monomeric and dimeric forms (D1, D2, and D3) of hydantoin molecule were done using DFT method employing 6–31++G(d, p) basis set. Harmonic and anharmonic wavenumbers and infrared intensities were computed at the same theory level. Experimental IR spectrum was recorded in the region 400–4000 cm−1. It has also been characterized by 1H and 13C NMR spectrum. The hydrogen bond (HB) interaction of hydantoin was analyzed via dimers of hydantoin. Detailed vibrational wavenumber shifts and all vibrational mode analyses were reported. Total energy distributions (TED, %) calculations were done to characterize the fundamentals.

Dynamics of frequency-modulated soliton-like pulses in a longitudinally inhomogeneous active optical waveguide

Abstract: Conditions of the formation and amplification of frequency-modulated soliton-like pulses in longitudinally inhomogeneous active optical waveguides with anomalous dispersion of group velocities are studied. Group velocity dispersion profiles that are necessary for existence and amplification for active and passive optical waveguides are determined, and the dependences on the distance passed along the waveguide, duration, and chirp of the pulse are established.

Temperature Dependence of the Luminescence of Li 6 Gd x Y 1 - x (BO 3 ) 3 :Eu Crystals

Abstract: The luminescence and recombination processes in crystals of lithium borates Li6Gd x Y1 − x (BO3)3:Eu (LGYBO:Eu) have been studied. The photoluminescence (PL) spectra upon selective photoexcitation to lower excited states of Gd3+ and Eu3+ ions and the temperature dependences of the photoluminescence intensity at different energies of excitation photons have been measured in a wide temperature range: 10–500 K. We observed a photoluminescence band at 3.97 eV, which is due to the 6 P J → 8 S 7/2 transitions in Gd3+ ions, and a characteristic line spectrum in the range of 1.6–2.2 eV, which is related to the radiative f-f transitions in impurity Eu3+ ions, occurring mainly from the lower excited 5 D 0 level to the 7 F J states (J = 0, 1, …, 6). The influence of the O-Eu charge transfer states and the vibrational relaxation between the 6 I J and 6 P J levels of the Gd3+ ion on the temperature dependences of the intrinsic and impurity luminescence intensities is discussed.

Spectral, luminescent, photochemical, and laser properties of a series of boron fluoride complexes of dipyrrolylmethenes in solutions

Abstract: We have studied the spectroscopic and lasing characteristics of active media based on two synthesized boron fluoride complexes of alkyl-substituted dipyrrolylmethenes and the photostability of the complexes in comparison with complexes of this kind that were previously studied in the literature under identical excitation conditions. We have determined and analyzed conditions under which new compounds have either merits or drawbacks as compared to the known dye with respect to both lasing efficiency and resource characteristics.

Study of opto-mechanical characteristics of interaction of ultrashort laser pulses with polymer materials

Abstract: The opto-mechanical characteristics, such as the specific mechanical recoil momentum, the specific impulse, and the energy efficiency, of the laser ablation of flat polymer targets ((C2F4) n , (CH2O) n ) have been determined experimentally for the first time for the case of excitation with femtosecond pulses (τ ∼ 45–70 fs) of UV-IR (λ ∼ 266, 400, 800 nm) laser radiation (I 0 up to 1015 W/cm2) under normal atmospheric and vacuum (p ∼ 10−4 mbar) conditions The efficiency of mechanical recoil momentum generation is analyzed for various regimes of the laser irradiation

Pulsed photo- and cathodoluminescence of LiF crystals doped with tungsten oxide

Abstract: We have studied the spectral and kinetic characteristics of activated photo- and cathodoluminescence of LiF-O and LiF-WO3 crystals in the spectral range of 3.6–1.6 eV using methods of pulsed spectrometry with nanosecond time resolution in the temperature range of 15–300 K and in the range of ionizing radiation dose absorbed by crystals of 102−2 × 103 Gy.

Spectrophotometric determination of bisoprolol in pharmaceutical preparations by charge transfer reactions

Abstract: A simple, rapid and sensitive method for the spectrophotometric determination, of bisoprolol was developed. The proposed methods were based on the charge-transfer reactions of bisoprolol, as n-electron donor, with 7,7,8,8-tetracyanoqumodimethane (TCNQ) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as π-acceptors to give highly colored complexes. The proposed methods were validated according to the ICH guidelines with respect to linearity, limit of detection, limit of quantification, accuracy, precision, recovery and specificity. Beer’s law is obeyed over the concentration ranges of 10–60 and 10–80 μg/mL bisoprolol with TCNQ and DDQ, respectively. The proposed methods were successfully applied to the assay of bisoprolol in pharmaceutical preparations.

A jet-type singlet oxygen generator based on porous fullerene-containing structures

Abstract: The results of studying the efficiency of singlet oxygen generation under optical pumping of solid-state fullerene-containing structures in a wide range of experimental conditions are presented. A description of a singlet oxygen generator based on porous fullerene-containing structures optically pumped by a light emitting diode (LED) matrix and enabling a continuous molecular oxygen flow through the porous substrate structure onto the irradiated fullerene surface is provided.

The efficiency of relief-phase diffractive elements at a small number of Fresnel zones

Abstract: A technique and investigation results are presented on the effect of the number of Fresnel zones on the diffraction efficiency and quality of the wave front formed by a diffractive optical element. Equations are presented for the microstructure reliefs of diffractive optical elements making (regardless of the number of Fresnel zones) the wavefront shape coinciding with the calculated one and ensuring 100% diffraction efficiency at a single wavelength and, in the case of two-layer structures, almost 100% diffraction efficiency in a wide spectral range.

IR spectra of benzaldehyde and its derivatives in different aggregate states

Abstract: We have measured the IR Fourier-transform spectra of biologically active benzaldehyde and its derivatives in the gas and liquid phases. For compounds of this class, the role played by C=O, OH, and CH groups in intra- and intermolecular has been analyzed. We have revealed spectral features that characterize the participation of C=O groups of unsubstituted benzaldehyde molecules in the occurrence of intermolecular hydrogen bonds C=O...H-C with the formation of molecular dimers of different types. For 2-hydroxybenzaldehyde molecules, spectral data have been obtained that are indicative of the occurrence of intramolecular hydrogen bonds of the C=O...H-C type in solutions. In 2-methoxybenzaldehyde molecules, no intramolecular hydrogen bonds have been observed.

Third harmonic generation in the field of a backward pump wave

Abstract: Third harmonic generation in a nonlinear medium the refractive index of which is negative at the pump frequency and positive at the harmonic frequency with allowance for self-action effects is considered theoretically. An exact solution of equations that describe the parametric interaction of continuous waves has been obtained analytically. The behavior of the solution is analyzed depending on the degree of violation of the phase matching condition. It is shown that, in a definite domain of values of nonlinear susceptibilities of the third order, there exists a critical value of the phase detuning at which the monotonic transform of the pump into the harmonic is changed by a periodical one. This phenomenon does not occur when the third harmonic is generated in ordinary media with a positive refractive index.

Holographic prism as a new optical element: III. Experimental implementation of a holographic prism of modification II and comparative characterization of the two holographic prism modifications from the application point of view

Abstract: The conditions for the formation of a holographic prism of modification II (for which a beam of diffracted rays is induced by a reference laser beam in the plane oriented perpendicularly to the reference beam) are described. A sample of this prism is implemented experimentally, and its response to the signal (reference) beam is demonstrated. Two modifications of a holographic prism as a basis for solving metrological problems of storing and reproducing flat angles and transferring the angle size to gradable and/or calibrated angle-measuring tools are compared. Each modification is found to have advantages in particular fields; thus, none can be considered as unconditionally preferred. The final choice of a particular modification can be made only after detailed analysis of the devices on their basis.

Emission of a spatially modulated resonant medium excited with superluminal velocity

Abstract: Specific characteristics of the radiation of a resonant medium excited by an ultrashort light pulse propagating through the medium with a superluminal velocity are considered. The medium is assumed to consist of identical linear harmonic oscillators with a spatial density periodically modulated along the direction of propagation of the superluminal excitation. The field of radiation of the resonant medium under these conditions is calculated. It is shown that, under the superluminal excitation, the radiation spectrum of the medium shows, along with the fundamental frequency of the oscillators, new frequencies that depend on the spatial frequency of the distribution of oscillators and on the angle of observation. Possible application of the effect is discussed.

Mutual modification of silver-nanoparticle plasmon resonances and the absorptive properties of polymethine-dye molecular layers on a sapphire surface

Abstract: Extinction spectra of a hybrid material comprised of molecular layers of polymethine dyes and granulated silver films preliminarily deposited onto sapphire substrates are studied experimentally. Specific features of the dye layer composition and broadening of plasmon absorption bands are discussed. In hybrid samples, both an increase and a decrease in the silver-nanoparticle plasmon resonance frequency upon spreading of dyes have been observed, as well as a considerable increase in the dye molecule absorption. Possible mechanisms of the phenomena are discussed.

DFT simulations, FT-IR, FT-raman, and FT-NMR spectra of 4-(4-chlorophenyl)-1H-imidazole molecules

Abstract: The FT-IR, FT-Raman and FT-NMR spectra of the compound 4-(4-Chlorophenyl)-1H-imidazole (4-ClPI) was recorded and analyzed. Density functional method has been used to compute optimized geometry, vibrational wavenumbers and NMR spectra of the 4-ClPI. Only one tautomeric form was found most stable by using B3LYP functional with the 6–311++G(d,p) as basis sets. The detailed interpretation of the vibrational spectra was carried out with the aid of total energy distribution (TED) following the scaled quantum mechanical force field methodology.

Observation of the luminescence of singlet oxygen at λ = 1270 nm under LED irradiation of CCl 4

Abstract: The efficiency of singlet-oxygen generation under optical pumping of oxygen dissolved in CCl4 has been analyzed using light-emitting diode arrays at three wavelengths (465, 525, and 625 nm), with direct recording of singlet-oxygen luminescence from the volume of irradiated solvent. The results obtained are compared with the efficiency of singlet-oxygen generation using C60 dissolved in CCl4 as a photosensitizer; it is shown that the efficiencies of singlet-oxygen generation differ by four orders of magnitude (on average) for only the radiation at the input of the solvent volume under study. The quantum yield of singlet oxygen upon direct optical excitation is about unity with respect to the optical-pump radiation absorbed in the solvent volume.

On the shape of cross resonances in counterpropagating wave spectroscopy

Abstract: Physical processes that generate cross resonances are studied. It is revealed that not only populational, but also coherent, effects can make a contribution to formation of cross resonances. The effects of coherent processes, lifetimes of levels, the parameter of radiation branching from the upper level, and light fields’ characteristics are shown to be qualitatively different for the Λ-, V-, and J = 1 − J = 1 types of transition. Conditions for the change in the sign of cross resonances are found and a situation wherein the cross resonance has a purely coherent nature is shown.

Theoretical investigations on the molecular structure and vibrational spectral analysis of 4-methyl 2-phenylimidazole

Abstract: The FT-IR, FT-Raman and FT-NMR spectra of 4-Methyl-2-phenylimidazole (4M2PI)molecule was recorded and analyzed. The tautomeric, structural and spectroscopic analysis of the title molecule was made by using density functional harmonic calculations. For the title molecule, only one tautomeric form was found most stable structure by using B3LYP level with the 6-311G++(d,p) as basis set. Selected experimental bands were assigned and characterized based on the scaled theoretical wave numbers by their total energy distribution (TED).

Relaxation processes with participation of excited S 1 and T 1 states of spatially distorted meso -phenyl-substituted octamethylporphyrins

Abstract: We have performed comparative analysis of the spectral properties and photophysical parameters of spatially distorted octamethylporphyrins (OMPs) upon varying the number (from one to four) and position of bulky meso-phenyl substituents in liquid solutions at 293 K and in solid media at 77 K. It has been substantiated that, for the series of studied compounds, which are characterized by a high degree of nonplanar distortions, considerable changes in the spectral-kinetic properties of singlet and triplet states at 293 K in liquid solutions are determined by the dynamic relaxation of the tetrapyrrole macrocycle that is caused by steric interactions of meso-phenyls with neighboring bulky groups β-CH3. The decay of T 1 states of mono- and di-meso-phenyl-substituted (trans) OMP molecules in liquid solutions has a biexponential character, which is indicative of conformational rearrangements of the macrocycle in the T 1 state. We are the first to measure the phosphorescence of spatially distorted metal-free OMP molecules in solid solutions at 77 K. It has been sub-stantiated that the decrease in the phosphorescence lifetime and quantum yield observed in the series of studied compounds with increasing number of meso-phenyl substituents at 77 K is related to a gradual increase in the probability of the nonradiative intersystem crossing, caused by the lowering of the energy of the T 1 level. We have revealed that spatially distorted tetrapyrrole macrocycles in rigid media at 77 K in the ground state are represented by two conformations. It has been found that the oxygen quenching rate constants of excited S 1 and T 1 electronic states of planar and spatially distorted porphyrin molecules are close to each other and depend weakly on the character distortion of the macrocycle. We have shown that the singlet oxygen generation quantum yield (γδ) of studied compounds depends on the number of meso-phenyl substituents in the OMP molecule and is determined by the character of the conformational dynamics of the tetrapyrrole macrocycle at 293 K.