Optics and Spectroscopy (v.95, #6)

A study of laser action on a free-molecular flow of atoms in a capillary by A. M. Bonch-Bruevich; T. A. Vartanyan; S. G. Przhibel’skii; V. N. Smirnov; V. V. Khromov (827-829).
We found experimentally that resonance laser irradiation of a rarefied flow of atoms in a capillary causes their density at the exit to decrease. We established a dependence of the change in atomic density on the excitation intensity. The observed effect is shown to be related to the flow heating caused by hyperelastic collisions of excited atoms with the capillary wall. We describe the gas heating in a capillary taking into account the energy relaxation of hot atoms as they collide with the wall. We show that our experimental results can be explained by assuming that the energy accommodation coefficient for hot atoms during their collisions with the wall is close to unity.

Lasing of iodine in the fullerene-oxygen-iodine system by V. P. Belousov; I. M. Belousova; A. S. Grenishin; O. B. Danilov; V. M. Kiselev; A. V. Kris’ko; A. A. Mak; T. D. Murav’eva; V. N. Sosnov (830-832).
The possibility of lasing in the fullerene-oxygen-iodine system with optical excitation of fullerene is studied. Laser radiation with an energy of 25 mJ and a pulse duration of 5–10 ms is obtained.

Generation of singlet oxygen with the use of optically excited fullerenes and fullerene-like nanoparticles by O. B. Danilov; I. M. Belousova; A. A. Mak; V. P. Belousov; A. S. Grenishin; V. M. Kiselev; A. V. Kris’ko; A. N. Ponomarev; E. N. Sosnov (833-842).
Experimental results and a kinetic model of generation of singlet oxygen during the interaction of oxygen molecules with optically pumped (lamp or laser radiation) fullerenes or fullerene-like nanoclusters in solutions, suspensions, and the form of various solid-phase membranes (surfaces) are presented. The experimental data on the photoluminescence of singlet oxygen in solutions of fullerenes are compared with the results of numerical simulation on the basis of the kinetic model with specified constants of photochemical processes. On the basis of the experimental results, it is shown that evaporation of a solution caused by pumping radiation yields long-lived gas-phase singlet oxygen. Release of gas-phase singlet oxygen from solid-phase fullerene-containing membranes (surfaces) is also demonstrated; however, this process is hindered by adsorption of singlet oxygen on the membrane surface. The prospects for creation of a singlet-oxygen generator on the basis of photoexcited fullerene molecules and fullerene-like nanoclusters are discussed.

Nonstationary multivortex and fissionable soliton-like structures of laser radiation by N. N. Rozanov; S. V. Fedorov; A. N. Shatsev (843-848).
New types of nonstationary soliton-like structures of laser radiation were found in the mean field approximation by numerical simulation of a class A wide-aperture laser with saturable absorption. In the absence of frequency detunings, multivortex (with several wavefront dislocations distributed over the aperture) asymmetric rotating solitons were revealed, which can be interpreted as strongly coupled states of symmetric laser solitons with topological charges coinciding or differing in sign. In the presence of detunings between the central frequencies of the gain and absorption profiles and the frequency of the cavity mode, “biosoliton” regimes were obtained, which are characterized by the expansion of the initial localized structure and the periodic separation from it of fragments having similar dynamics.

Nonreciprocal waveguides and lenses based on the Fresnel-Fizeau effect by N. N. Rozanov; G. B. Sochilin; O. B. Danilov (849-851).
The propagation of a radiation beam in a medium whose velocity varies in the direction transverse to the axis of the beam is considered. It is shown that, under these conditions, the Fresnel-Fizeau effect of partial entrainment of light leads to focusing of the beam and to the possibility of the waveguide propagation of light. The corresponding waveguides and lenses have the property of nonreciprocity; i.e., their characteristics change with the reversal of the direction of propagation. The estimates obtained show the feasibility of observing the effect for optical radiation.

Modes of a rotating dielectric waveguide by N. N. Rozanov (852-855).
Proceeding from the Maxwell differential equations and the Minkowski constitutive equations of the first order with respect to the ratio of the velocity of motion of a medium to the velocity of light in a vacuum, we derived equations for determining the mode structure of a field in a linear isotropic medium with an axially symmetric distribution of the permittivity and the permeability and with the angular velocity of rotation dependent on the distance from the symmetry axis. A waveguide effect was shown to appear even for a homogeneous medium owing to the spatial nonuniformity of the angular velocity. In the case of the quadratic dependence of the angular velocity on the transverse coordinate, the exact solutions for the modes were found in the form of Gaussian beams.

Photodynamics of optical limiting upon two-photon excitation of a liquid crystal-perylene system by V. V. Danilov; E. N. Sosnov; O. V. Khapova; A. I. Khrebtov; T. A. Shakhverdov (856-864).
On the example of a model system—liquid crystal-perylene—the efficiency of the two-photon mechanism in solving problems of optical limiting and the prospects of using for these purposes radical ions that are formed due to the action of laser radiation on polycyclic compounds are shown. The role of luminescence quenching by light as a secondary nonlinear effect in the kinetics of optical limiting is considered in detail.

Fine structure parameters and fields of crossing of Zeeman sublevels in the 1snf(n=4–8) configurations of the helium atom by G. P. Anisimova; L. A. Volkova; R. I. Semenov; G. A. Tsygankova; I. Ya. Chubukov (865-868).
The fine structure parameters of five 1snf configurations of the helium atom, the intermediate coupling wave functions, and the gyromagnetic ratios are calculated in the single-configuration approximation. Virtually zero residuals between the calculated and experimental values of energies are obtained. For two configurations, 1s4f and 1s5f, the fields of Zeeman sublevel crossing for magnetic fields from 0 to 700 Oe and the regions of anticrossings are found.

A semiempirical least squares method is used to determine the wave functions for the intermediate coupling between the 4d 95s, 4d 95p, and 4d 95d levels in the XeIX-CeXIII spectra and to calculate the radiative lifetimes of the 4d 95p and 4d 95d levels in these spectra.

Shape of the Doppler absorption profile in measurements by magnetic scanning by I. V. Barybin; V. A. Sorokin; A. E. Churin (873-877).
In measurements of the absorption of single-frequency laser radiation at the 3s 2−2p 4 transition in neon performed by magnetic scanning, a noticeable asymmetry of the Doppler profile was revealed. This asymmetry was observed when the laser frequency was detuned from the line center. The sign of the asymmetric contribution to the shape of the Doppler profile is related to the sign of the detuning.

We experimentally studied the excitation of resonance transitions in a thulium atom in electron-atom collisions. At an electron energy of 50 eV, we measured 52 TmI excitation cross sections. We recorded 41 optical excitation functions in the electron energy range from the excitation threshold to 200 eV. The measured cross sections are, on average, a factor of 1.09 larger than their preceding experimental values but a factor of 2.41 smaller than their theoretical values.

Based on the system of equations describing the populations of highly excited helium atomic levels and the electron density and energy balance and on the Maxwell equations, we develop a model for an electrodeless high-frequency discharge in helium. We suggest a method of self-consistent calculation in a plasma-field system. The model developed is used to calculate the radiative characteristics of high-frequency electrodeless lamps. The derived dependences of line intensities on gas pressure, lamp radius, and discharge power are in good agreement with the experimental data.

The state of an atomic-molecular system near its stability threshold with regard to the detachment of one of the particles is studied. The decay of the system upon a decrease in the charge of a binding particle, as well upon an increasasymmetry of masses of like-charged particles, is considered. A special variational principle that allows one to directly calculate the threshold state of the system without repeatedly calculating its energy for different values of masses and charges of particles is used. With the motion of all particles fully taken into account, the threshold states of two-electron atoms with different nuclear charges and of atomic-molecular systems corresponding to the attachment of a positron of variable mass to a neutral atom are calculated. On the basis of calculation of quantum-mechanical expectation values of the kinetic energy of particles and the potential energy of their interaction, the rearrangement of the wave function upon passage of the system through the decay threshold is examined. The threshold characteristics of a purely adiabatic system containing infinitely heavy particles are considered separately.

For the first time, translational vibrations of a proton in H2O, D2O, HDO, and hexagonal ice were found in the Rayleigh line wing using four-photon polarization spectroscopy.

Luminescence of dipicolinic complexes of lanthanide ions by E. B. Sveshnikova; P. A. Shakhverdov; T. A. Shakhverdov; V. E. Lanin; R. U. Safina; B. M. Bolotin; V. L. Ermolaev (898-907).
The luminescence decay times τlum of the complexes of the ions Tb(III), Eu(III), Sm(III), Dy(III), and Yb(III) with dipicolinic acid (DPA) dissolved in protonated and deuterated water, methanol, and dimethyl sulfoxide are measured. The values of τlum for crystals H3[Ln(DPA)3nH2O and their aqueous solutions coincide, which points to the identity of the environment in the nearest spheres of an ion in both cases. A comparison of τlum of solutions of the complexes in H2O and D2O, as well as in CH3OH, CH3OD, CD3OD, DMSO-h 6, and DMSO-d 6 shows that the molecular groups in the second and third spheres of an ion, exhibiting high-frequency vibrations, have a noticeable effect on the rate constants of nonradiative transitions k nr in the ion. From this comparison, some inferences on the structure of the solvate shell of the Ln(DPA) 3 3− complexes in the solvents used are made. The contributions to k nr of Eu(III), Tb(III), Sm(III), Dy(III), Nd(III), and Yb(III) made by OH and CH groups located at different distances from the ion are estimated. It is demonstrated that the dependence of k nr on the distance to the OH and CH groups is steeper for the Eu(III) and Tb(III) ions than for the remaining ions.

The luminescence decay times τlum of the ions Sm(III), Eu(III), Tb(III), and Dy(III) in glacial acetic acid, along with τlum and q lum of these ions in H2O and D2O in the presence of anions CO 3 2− and in their absence, are measured. The number of OH groups (N OH) in the first coordination sphere of these lanthanide ions is determined. It was shown that, for all the ions in acetic acid, N OH≈3, while, in an H2O+2 M Cs2CO3 solution, N OH≈2.5. The experimental data on the influence of the CO 3 2− anions on the rate constant of nonradiative transitions (k nr) in the Eu(III) and Tb(III) ions are compared with calculations of k nr performed in the dipole-dipole approximation of the inductive resonance theory. It is found that such calculations cannot correctly describe the dependence of k nr on N OH. The quadrupole-dipole approximation of this theory was shown to be capable of adequately describing this dependence. The criteria for applying either approximation of the theory to describe experimentally observed dependences of k nr on N OH are discussed.

Spectral studies of tetrabutylammonium bis(thiocyanate-S)phenylpyridinate(C,N)platinate(II) by M. V. Puzyk; P. -I. Kvam; J. Songstad; K. P. Balashev (914-916).
The spectral and luminescent properties of tetrabutylammonium bis(thiocyanate-S)phenylpyridinate(C, N)platinate(II) were studied at 77 and 298 K in the polycrystalline state, frozen solutions, and polystyrene and polymethyl methacrylate films. The nature and properties of the electronically excited state of the complex responsible for its luminescence are determined.

Spectroscopy and photophysics of chloro-bis-bipyridyl complexes of ruthenium(II) with pyridine ligands by S. V. Litke; T. V. Mezentseva; G. N. Lyalin; A. Yu. Ershov (917-924).
The absorption, luminescence, and luminescence excitation spectra of ruthenium(II) complexes cis-[Ru(bpy)2(L)Cl]+[bpy=2,2′-bipyridyl; L=NH3, pyrazine, pyridine, 4-aminopyridine, 4-picoline, isonicotinamide, 4-cyanopyridine, 4,4′-bipyridyl, or trans-1,2-bis(4-pyridyl)ethylene] in alcoholic (4: 1 EtOH-MeOH) solutions are studied. At 77 K, the quantum yields and decay times of the luminescence of the complexes are measured and the deactivation rate constants of the lowest electronically excited metal-to-ligand charge transfer state (3MLCT) are determined. The linear correlation between the energy of the lowest state 3MLCT d π(Ru)>π*(bpy) of the cis-[Ru(bpy)2(L)Cl]+ complexes and the parameter pKa of the free 4-substituted pyridines and pyrazine used as ligands is established.

We investigate the characteristics of a broadband cylindrical excimer source of visible radiation with a surface area of 230 cm2 excited by a pulse-periodic barrier discharge based on multicomponent mixtures (mercury diiodide and dibromide with helium and admixtures of molecular nitrogen and xenon). The working mixture components were excited by a pulse-periodic (pulse repetition rate 500–5000 Hz, pulse duration ∼150 ns) barrier discharge. We detected radiation from excimer HgI* and HgBr* molecules, the second positive system of molecular nitrogen, and mercury and xenon atoms. The amplitude, duration, and trailing edge of the radiation pulses in the HgI2:HgBr2:Xe:He and HgI2: HgBr2:N2:He mixtures with admixtures of xenon and molecular nitrogen were found to change compared to the HgI2:HgBr2:He mixture. The optimal partial pressure of helium lies within the range 162–195 kPa. The most intense radiation from HgI* and HgBr* molecules (in a ratio of more than 3: 1) is observed in the HgI2:HgBr2: Xe:He mixture. The mean and pulse radiation powers are 45 W and 93 kW, respectively, at a pumping pulse repetition rate of 5000 Hz and an efficiency of 30%. We discuss the spectral and temporal characteristics of the radiation source and the dependence of the radiation intensity of excimer molecules of mercury monoiodide and monobromide on the partial pressures of xenon and nitrogen. We point out that the radiation source is of considerable interest for applications in biotechnology and medicine.

A method of photon correlation probing of spectral diffusion at ultralow temperatures is suggested for polymer glasses. The method makes it possible to determine the ensemble-averaged autocorrelation function of fluctuations in the spectra of individual chromophores from the fluctuations of the fluorescence intensity of a sample, as well as to select subensembles of impurity molecules by the amplitudes of spectral jumps of their absorption lines due to the transitions of molecules between equilibrium states closely spaced in energy. The method has a number of advantages in comparison with the conventional methods of investigation of spectral diffusion: single-molecule spectroscopy, hole-burning spectroscopy, and the measurement of hole broadening with time.

Results of computer simulation of light scattering by powderlike media composed of large semitransparent particles of different shapes are presented. The geometrical optics approach is used. The cases of particles of spherical, cubic, and random shapes are considered. The one-dimensional geometrical optics model of light scattering by powderlike media, which finds application in investigations of planetary surfaces, meteorites, and lunar samples, is briefly described. The numerical simulation allowed us to estimate the error of this model, which turned out to be within the limits of several percent. The albedo calculated by using the one-dimensional model is shown to be closest to the “three-dimensional” reflectance of the surfaces at a phase angle of about 60°. This albedo also approximates fairly well the integrated reflectance, which in laboratory measurements is determined with the help of an integrating sphere.

The situations are considered in which the differential equation for calculating the transmission 2×2 matrix of a smoothly inhomogeneous anisotropic medium in the approximation of negligible smallness of the bulk reflection (NSBR) can be solved analytically. The general expression for this matrix is obtained for the case of normal incidence of light on an arbitrary ideally twisted optically locally centrosymmetric medium. It is shown that, under certain conditions of normalization of the eigenwave basis, the solutions obtained in the NSBR approximation are as simple as those obtained in the approximation of a small anisotropy, but the accuracy of the former solutions is significantly greater. It was shown that, generally, the determinant of the transmission 2×2 matrix of a smoothly inhomogeneous anisotropic medium can be expressed in terms of the parameters of the eigenwave basis, while, in the case of a locally inhomogeneous anisotropic medium, this value is expressed in terms of the parameters of the medium. This circumstance can be used in solving inverse problems.

The diffraction efficiency and light-scattering power of holographic gratings formed on the surface of a two-layer photothermoplastic carrier with a pit structure of deformation are studied. The influence of the height and regularity of the pit deformation on the diffraction efficiency and light-scattering power is studied. It is shown that the pronounced resonance character of the dependence of the diffraction efficiency on the spatial frequency in the case of pit deformation is related to the distribution of the deformation depth over spatial frequencies; however, the dominant factor is the mutual arrangement of pits within the interference fringe. It is found that the light-scattering power is determined for the most part by the size and density of the deformation. A new method is proposed for determining the resolution of photothermoplastic carriers with pit deformation, which apparently can be used for photothermoplastic carriers with any irregular structure of deformation. This method is based on the analysis of the dependence of the light-scattering power of holographic gratings on their spatial frequency. It is shown that the resolution depends inversely proportionally on the thickness of the thermoplastic layer of the optical carrier.

Results of calculations of intensities, losses, and frequencies of counterpropagating waves in a ring resonator containing a weakly nonlinear active medium and an aperture are given. It is shown that inequalities of frequencies and intensities of generation of counterpropagating waves occur in such a resonator. The behavior of these inequalities is determined by the nonreciprocity of frequency-dependent losses of the counterpropagating waves.

Nonlinear properties of composites based on dielectric layers containing copper and silver nanoparticles by R. A. Ganeev; A. I. Ryasnyanskii; A. L. Stepanov; M. K. Kondirov; T. Usmanov (967-975).
Nonlinear optical characteristics of copper and silver nanoparticles in glass host matrices are studied by the Z-scan method at the wavelength of a Nd:YAG laser (λ=1064 nm) in a field of picosecond pulses. It is found that the third-order nonlinear susceptibility is more pronounced in glasses with copper nanoparticles than in glasses with silver nanoparticles. On the basis of experimental data obtained for samples with copper nanoparticles synthesized by ion implantation, it is shown for the first time that the nonlinear absorption of laser radiation with a wavelength lying out of the plasmon resonance region can be caused by a two-photon effect in metal particles. The character of the optical limiting process in the samples with copper nanoparticles when two-photon absorption is involved is discussed.

Numerical calculation of second harmonic generation in a photonic crystal consisting of alternating quarter-wave layers of ZnS and SeF2 pumped by a femtosecond tunable laser is carried out. The results are compared with the spectral characteristics of the photonic crystal obtained with the use of a matrix method for calculating transmission coefficients. It is shown that the maximum efficiency of conversion to the second harmonic takes place at a minimum group velocity mismatch of the pump and second harmonic waves, corresponding to pump frequencies in the range below the band gap edge of the photonic crystal.

Laser sounding of molecular iodine in the atmosphere by V. E. Privalov; V. G. Shemanin (983-987).
The lidar equation for the fluorescence of 127I2 molecules is numerically solved. All the radiation wavelengths of a copper vapor laser are considered with the aim of choosing the one that is the most appropriate for detection of the minimum possible concentration of iodine molecules when this laser is used as a radiation source of a fluorescence lidar.