Optics and Spectroscopy (v.89, #3)

Different types of vector couplings (model representations) are considered, and their role in semiempirical calculations is clarified. For the simplest sl-configurations, the representation space is introduced, which illustrates the relationship between different coupling types. The relation between the vector model and the quantum-mechanical model is demonstrated.

Multiphoton resonant ionization in the case of a doubly degenerate intermediate bound state is studied. In the Keldysh-Feisal-Reiss approach, expressions for the energy and angular photoelectron distributions and the quasi-classical formula for the total rate of resonant ionization are obtained. It is shown that the ionization rate may be both higher and lower than the ionization rate in the usual case depending on the relationship between parameters. A situation with a strongly suppressed probability of resonant ionization is possible. In the near-threshold region, the angular dependence of the probability of photoelectron escape is shown to be weaker in comparison with the case of ionization via a nondegenerate level.

Anomalous elastic scattering of X-rays by a multiply chargedion by A. N. Khoperskiĭ; V. A. Yavna; S. A. Novikov; M. E. Vasil’eva (334-335).
Absolute values and the form of the differential cross section for anomalous elastic scattering of an X-ray photon by a Ne6+ ion near the ionization threshold of the 1s shell are calculated. The many-particle effect of deep-vacancy stabilization caused by a change from a neutral atom to its multiply charged ion is taken into account. The calculation results are predictable.

The method of extended crossing beams with the recording of an optical signal from an intersection region is used to study the excitation of a singly charged lanthanum ion. The process in question is accomplished in a single collision event between a lanthanum atom and an electron, i.e., as an excitation process with simultaneous single ionization. Excitation cross sections for 105 spectral lines arising upon transitions from odd triplet levels of LaII are measured. Also recorded are 16 optical excitation functions for 85 lines. The results obtained are used to calculate the cross sections for excitation of the energy levels and the contribution of cascade transitions to their population.

Spectroscopic diagnostics of carbon and aluminum laser-produced plasmas by G. Ts. Nersisyan; V. O. Papanyan (344-347).
VUV emission spectra of plasmas produced by focusing laser radiation with intensity of 1010–1011 W/cm2 on carbon and aluminum targets were studied. Using the partial local thermodynamic equilibrium model for an electron density exceeding 1017 cm−3, the spectroscopic diagnostics and the analysis of ion composition of plasmas were carried out. The electron temperatures determined for carbon and aluminum plasmas from the ratio of intensities of ionic lines were found to be 8±3 eV and 11±4 eV, respectively. Stark broadening of aluminum lines was measured and parameters of electron broadening were determined. Using the spatially resolved measurement of Stark line broadening, the spatial density distribution and the law of electron gas expansion were found. The electron gas in the hot region of size 5 mm with an average density of (5±2) 1017cm −3 experienced one-dimensional expansion according to the law 1/z 1.1 with increasing distance z from the target.

A method for diagnostics of a magnetic field is suggested. The method is based on spectropolarimetry of the decaying emission of an ensemble of particles whose angular momenta were ordered by pulsed axially symmetric perturbation.

Three issues of interest in the present stage of development of single impurity-molecule spectroscopy (SIMS) are discussed: (i) prospects of SIMS in quantum informatics, (ii) the possibility of SIMS realization by measuring the surface enhanced Raman scattering in solids, and (iii) concentration effects in SIMS and in persistent spectral hole burning.

The spectrum of absorption of light by a molecule colliding with a fast proton is considered. It is shown that the envelope of spectrum is an oscillating function with two maxima shifted toward lower and higher frequencies compared to the frequency of a Franck-Condon transition.

We studied sensitization of Eu(III) and Tb(III) ions by molecules of 1,10-phenanthroline and 2,2-bipyridil in D2O and d 6-ethanol and the influence of Nd(III), Pr(III), Sm(III), Gd(III), and Ho(III) ions on the luminescence intensity I lum and lifetime τlum of Eu(III) and Tb(III) in solutions. The stability constants of complexes of Eu(III) and Gd(III) with 2,2′-bipyridil are measured by spectrophotometric and luminescence methods. It is shown that luminescence of Eu(III) is quenched by Gd(III) ions at the ion concentration equal to 10−2–10−1 M, which is caused by competing between these ions for a sensitizer. At the concentration of Ln(III) ions equal to 10−6−10−3 M, the sensitized luminescence of Eu(III) and Tb(III) was quenched and τlum decreased in the presence of Nd(III) ions, whereas in the presence of Gd(III) the luminescence intensity increased. It is proved that a bridge that connects the two ions upon energy transfer is formed by hydroxyl groups. The intensity of luminescence of Eu(III) and Tb(III) in aqueous solutions and its lifetime decreased in the presence of hydroxyl groups, while upon addition of Gd(III) to these solutions these quantities were restored. We also found that the addition of Gd(III) to deoxygenated ethanol solutions of 2,2′-bipyridil and Eu(III) slows down photochemical and thermal reactions between bipyridil and Eu(III), resulting in the increase in the luminescence intensity of Eu(III).

Effect of fullerenes C60and C70 on the absorption spectrum of 2-cyclooctylamino-5-nitropyridine by N. V. Kamanina; V. S. Vikhnin; A. Leyderman; A. Barrientos; Y. Cui; M. Vlasse (369-371).
The influence of fullerenes C60 and C70 on the absorption spectrum of 2-cyclooctylamino-5-nitropyridine (COANP) is studied. A substantial shift of the absorption band edge of COANP-C70 to the IR region was observed. This effect was compared with the data obtained for COANP-C60. The experimental results were explained using the model that takes into account the interaction between electronic subsystems of COANP and fullerene.

Resonance Raman spectra of the Ca2CuO3 cuprate by Ya. S. Bobovich; V. N. Denisov; B. N. Mavrin; T. I. Chuvaeva (372-375).
Ceramics of the Ca2CuO3 cuprate with a purely chain copper-oxygen structure is synthesized. The Raman spectra of ceramic samples are recorded upon excitation in a broad spectral range from the blue-green to near-IR region. The intensities of a number of lines and bands of different scattering orders are estimated using the internal reference method. The results are compared with physical and chemical models of the process.

By analogy with the Wigner-Weisskopf model, spontaneous emission of an atom is considered in a spatially periodic field of the resonance counter-propagating waves. The Bloch state obtained by the interaction of the initially excited (unexcited) atom with a field of the counter-propagating waves plays the role of the excited (ground) state of the free atom. The spontaneous emission probability averaged over polarizations is shown to become anisotropic, with the symmetry axis directed along the wave propagation path. The anisotropy is caused by the spatially periodic distribution of the wave function of the translational motion of an atom in the external field. The degree of anisotropy depends on the position of Bloch energy levels in the allowed bands of the energy spectrum.

Conditions for the existence of laser bullets by N. A. Veretenov; A. G. Vladimirov; N. A. Kaliteevskii; N. N. Rozanov; S. V. Fedorov; A. N. Shatsev (380-383).
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.

Propagation of two waves in a transparent one-dimensional medium with cubic nonlinearity is analyzed. Correlation between the two beams develops, which periodically changes with the length of a medium and is quantum or classical in nature. Mutual correlation between the waves in this medium may be enhanced without destruction in the resonant one-photon amplification process.

A new method for the analysis of light scattering by a nonspherical penetrable microparticle located on the substrate surface is developed. A computational algorithm is constructed on the basis of generalization of the method of discrete sources. The results of a numerical simulation are discussed.

The estimate of the root-mean-square roughness of a rough surface σ1 is studied experimentally as a function of the angle of incidence. A surface with σ=1.3 μm is illuminated by laser radiation with a wavelength of 0.633 μm. The angle of incidence of radiation on the surface under study is varied from 85° to 87.5°. σ1 is estimated under the assumption that the regime of a slightly rough surface is fulfilled for the surface studied. Theoretical estimates of σ1 are calculated in the Kirchhoff approximation with rough surface shadowing taken into account. The greatest relative difference between experimental and theoretical estimates of σ 1 does not exceed 0.07. The effect of rough surface shadowing on the estimate of σ is analyzed, and the possibility for exact measurement of σ1 of a shaded rough surface is demonstrated in the case of a priori knowledge of the angle of incidence, for which this measurement is possible. A method that makes it possible to determine the angle of incidence, for which a good agreement between the measured value and the true value of σ of a shaded rough surface is possible, is proposed.

Optical method for measuring structural parameters of island films by A. M. Bonch-Bruevich; T. A. Vartanyan; N. B. Leonov; S. G. Przhibel’skii; V. V. Khromov (402-407).
An optical method for determining characteristics of the submicron structure in island films is proposed. The method is based on the measurements of fluctuations of optical properties of a film detected when a focused laser beam is scanned over it. It is shown that the island size distribution can be determined in principle by the method proposed. Structural inhomogeneity of a Cs film on sapphire is revealed experimentally. Parameters of these inhomogeneities are measured as functions of the film thickness. The correspondence of the results of the optical method and the data of electron microscopy is tested for a In film on glass.

Dielectric layers with silver nanoparticles, which are synthesized in a soda-silicate glass by implantation of 60-keV ions with a dose of 7.0×1016 Ag+/cm2 at an ion current density of 10 μmA/cm2, are analyzed. The depth of silver distribution was measured by Rutherford backscattering. Data on optical characteristics of composite layers were obtained from the transmission spectra and from the reflection, which were measured both from the side of an implanted glass surface and from the unimplanted side. To calculate reflection spectra, a multilayer plane-parallel film structure was considered, which was modeled on the basis of the matrix method using complex Fresnel coefficients. Dielectric functions of separate layers were determined using the Maxwell-Garnet theory of an effective medium. A qualitative agreement between the experimental and the model optical spectra was obtained taking into account a nonuniform depth distribution of metal nanoparticles in a composite material.

Spectroscopic studies of sorbing fibers using combined elements with multiple attenuated total internal reflection by R. K. Mamedov; I. V. Malinin; B. Z. Volchek; A. S. Bobasheva; B. V. Stolyarov; A. G. Enikeeva (413-417).
Spectroscopic studies of sorbing devices on the basis of silica capillaries coated by sorbing polymer films are carried out by methods of spectroscopy of multiple attenuated total internal reflection with the use of combined elements of internal reflection. A technique for inspecting and improving the technological process of manufacture of sorbing devices for solid-phase microextraction and subsequent chromatographic analysis of organic compounds is developed.

A mechanism of controlling light is studied, which is based on the change of refractive indices of narrow-gap layers in a semiconductor layered periodic Fabry-Perot type structure (superlattice) caused by the contribution of nonequilibrium charge carriers produced by controlling radiation. By choosing the wavelength of controlling light near the edge of intrinsic absorption of narrow-gap layers and by choosing the wavelength of controlled light near the edge of the band gap of a structure, one can obtain for 1.5-μm controlled radiation the modulation depth above 90%, with controlling radiation intensity of ∼6 kW/cm2.

A version of perturbation theory is developed that intends to determine the field distribution of spatial solitons with a 2D transverse profile in a Kerr medium in the case of small deviations from paraxial conditions. An approximate master equation for transverse components of the electric field in the case of wide solitons is derived. By solving this equation starting from the unperturbed soliton, i.e., Townes mode with linear polarization of radiation, a solution with an axially symmetric field distribution is found. Dependences of the main soliton characteristics on the degree of paraxiality are determined.

Kinetic theory of photon density waves by V. L. Kuz’min; V. P. Romanov (429-437).
A kinetic equation is obtained for the modulated intensity of multiply scattered light, which generalizes the known Bethe-Salpeter equation. An asymptotic solution is found in the P 1 approximation, which takes into account the anisotropy of single scattering within the average cosine of the scattering angle. The parameters of the photon density wave are calculated from this solution. It is shown that the relative phase shift and modulation degree calculated for modulation frequencies exceeding several gigahertz noticeably differ from the values predicted by the radiation transfer equation.

Integral light-scattering indicatrix of optically soft spherical particles by N. V. Shepelevich; I. V. Prostakova; V. N. Lopatin (438-444).
The dependences of the angular distribution of the scattered energy on the particle size and refractive index and on the phase shift (Δ) were studied. It was shown, in particular, that in the hypsometric plane for Δ≥3, the light-scattering indicatrix F calculated by the Mie theory is determined by two factors: the Fraunhofer diffraction and geometrical optics. The possibility of measuring the refractive index from the experimental values of the aperture angle of a photodetector at fixed values of F was also considered.

It was shown that in processes involving absorption or stimulated emission of n photons of a partially polarized wave, polarization must be described by n(n+2) real independent parameters (the nth-order polarization parameters). Description of polarization by means of three parameters, e.g., the Stokes parameters, and the use of the photon density polarization matrix is justified only when one considers one-photon processes or intensity transmission of a polarization filter. The second-order polarization parameters were expressed in terms of directly measurable quantities (intensity correlation functions), and their relation to the Stokes parameters was established. The simple example of unpolarized (natural) light was considered, and the explicit form of the two-photon polarization matrix was derived for that case. It was also shown that the natural light is unpolarized in all orders and that zero Stokes parameters, in particular, do not necessarily mean that the light is unpolarized.

Based on phenomenological concepts of statistics of effective optical paths for multiple scattering of coherent radiation, an analysis is carried out of similarity effects observed for the dependences of statistical moments of the scattered field on the relaxation parameters with a dimension of reciprocal length. Within the framework of the diffusion approximation, expressions are obtained that describe the autocorrelation function of fluctuations of the scattered-field amplitude, the degree of polarization, and the normalized intensity of scattered light for media with a finite absorption length in the case of forward scattering of coherent radiation in a plane layer of an isotropic scattering medium. The results of the analysis show the similarity of the dependences of these quantities on the corresponding spatial scales. Experiments with model scattering media (aqueous suspensions of polystyrene spherical particles) supported the existence of similarity effects in multiple scattering. An experimental study was made of the relation between the characteristic depolarization length and the transport length for multiple scattering of coherent radiation in a plane layer. The effective value of the radiation diffusion coefficient providing the best agreement between the experimental and the calculated values of parameters of the scattered field is shown to be independent of the absorption coefficient of a medium.

Results of the studies of acoustooptical interaction in a lithium niobate crystal upon excitation of an elastic wave in the direction of the X-axis by a multielement piezoelectric transducer at frequencies about 10 GHz are presented. The experimental method is described. Frequency dependences of the diffracted light intensity and acoustic damping as well as the frequency resolving power are studied. Damping of longitudinal acoustic waves in X-cut lithium niobate is measured to be 1.05±0.02 dB/cm GHz. The maximum diffraction efficiency reached 1% for 1 W of electromagnetic power supplied. The frequency bandwidths at the levels of 3 and 6 dB of the maximum value are 2.5 and 3 GHz, respectively. The frequency resolution is 15 MHz at the frequency of 9 GHz.

Polarization aberrations of laser radiation by A. L. Sokolov (469-475).
Polarization aberrations (PAs) of laser radiation, defined as distortions of the wave-polarization characteristics, are considered within the framework of wave theory. The parameters describing these aberrations are introduced. It is established that PAs already appear in the paraxial region. PAs of a thin lens are calculated using the method of wave-polarization matrices. It is shown that, under certain conditions, the polarization state is modified at the axis of the laser beam.

Results of experiments on recording three-dimensional holographic images of extended diffuse objects using an SHG hologram generating the second harmonic are presented. In this case, the object image is formed by the second-harmonic radiation whose wavelength is smaller than the wavelength of object and reference waves recorded on a hologram by a factor of two. Elements of the theory of an SHG hologram are considered. A holographic image of a transparency object illuminated with diffuse light is obtained. It is shown that the resolving power of this image is close to the limit determined by diffraction effects. An experiment on defocusing the reconstructed image showed that it was localized in one spatial plane and, therefore, was three-dimensional.