Optics and Spectroscopy (v.119, #3)

Radiative transitions in quasi-molecules by A. Z. Devdariani (333-337).
Radiative transitions occurring at atomic collisions are considered. Attention is focused on the transitions that are either impossible in individual atoms or ions or forbidden by the selection rules. The excitation of continuous-spectrum electron states is considered for the first time by an example of photodetachment at collisions of negative ions with neutral atoms.

It is shown that heating of potassium–aluminum borate glasses with CuCl nanocrystals above 80°C leads to the disappearance of exciton absorption peaks, whereas cooling below 50°C gives rise to these peaks. These effects are related, respectively, to the melting of nanocrystals and crystallization of nanophase.

Nanostructural antireflecting coatings: Classification analysis (A review) by K. V. Baryshnikova; A. S. Kadochkin; A. S. Shalin (343-355).
Many modern optical instruments require the use of high-quality antireflecting coatings. Singleand multilayer homogeneous films are mainly used for this purpose. However, an alternative line is rapidly developed at present, which is devoted to the design and use of nanostructural systems for increasing the transparency of different media. Despite the unified principle of operation of these coatings, which is based on the destructive interference of waves in the direction of reflection of light, approaches to their implementation may differ significantly. Different types of nanostructural coatings are considered in detail and classified, their optical properties are compared, and special attention is paid to methods of their manufacture. It is shown that different antireflecting coatings should be used for different purposes, and that coatings that combine properties of several classes often have better antireflecting capabilities.

Frequency conversion of radiation of IR molecular gas lasers in nonlinear crystals (A review) by A. A. Ionin; I. O. Kinyaevskiy; Yu. M. Klimachev; A. A. Kotkov (356-362).
The solution of problems related, e.g., to transport of laser radiation in the atmosphere requires availability of a broadband IR laser source operating in the transparency windows of the atmosphere. In this review, we present the results of an investigation of the properties of a hybrid laser system consisting of molecular gas pump lasers and a solid-state laser frequency converter based on nonlinear crystals. We demonstrate broadening and enrichment of spectrum of radiation of the pump laser by means of sum- and difference-frequency generation. In particular, by using a relatively simple laser system consisting of gas-discharge CO and CO2 lasers, radiation tunable over a large number of spectral lines in a broad range of wavelength from 2.5 to 16.6 µm (more than two and a half octaves), which includes two transparency windows of the atmosphere, is obtained. Thus, the possibility of exploring the IR spectral range by means of hybrid laser systems based on frequency conversion of radiation of molecular gas lasers is demonstrated.

Oscillons of Bose–Einstein condensate (A review) by N. N. Rosanov; N. A. Veretenov; N. V. Vysotina; L. A. Nesterov; S. V. Fedorov; A. N. Shatsev (363-370).
The dynamics of localized structures of atomic Bose–Einstein condensate in traps with oscillating walls has been analyzed. The properties of these oscillons localized in the longitudinal and transverse directions with respect to the trap axis are compared with the properties of conservative and dissipative solitons.

A brief review of theoretical studies of the quantum state of polarization of light exhibiting the level of fluctuations in at least one of the Stokes parameters which is below the quantum noise limit is presented. Two approaches to generation of polarization-squeezed state of light are analyzed in detail: by propagating coherent radiation in a cubic nonlinear medium and by mixing radiation of two orthogonally polarized quadrature-squeezed modes. The degree of polarization of light is discussed. Other areas of quantum polarization optics, in particular, entanglement of quantum Stokes parameters and quantum polarization tomography, are also discussed.

Random lasing in an inhomogeneous and disordered system of cold atoms by L. V. Gerasimov; D. V. Kuprianov; M. D. Havey (377-384).
We consider light trapping in an amplifying medium consisting of cold alkali-metal atoms; the atomic gas plays a dual role as a scattering and as a gain medium. We perform Monte-Carlo simulations for the combined processes. In some configurations of the inhomogeneous distribution this leads to a point of instability behavior and a signature of random lasing in a cold atomic gas.

Coherent spectroscopy with fast frequency swept lasers by S. N. Andreev; V. N. Ochkin; N. V. Pestovskii; S. Yu. Savinov (385-391).
Effects caused by fast laser frequency sweeping across absorption lines are investigated. Oscillations in the time dependence of intensity of radiation generated by the medium, which are caused by beats between oscillations at variable excitation frequency and constant eigenfrequencies, are discovered. The time intervals between local maxima of the oscillations are inversely proportional to the difference between the eigenfrequency of the atomic oscillator and the instant frequency of the external radiation. The method of using fast frequency sweeping for determining indices of absorption at high optical densities (k 0 z ~ 100) is proposed.

Optical diagnostics of the process of free liquid convection by B. G. Manukhin; M. E. Gusev; D. A. Kucher; S. A. Chivilikhin; O. V. Andreeva (392-397).
A technique for complex investigation of the process of free liquid convection under the action of a heat source is presented, which is based on the use of digital holographic interferometry. The mode of studying an object, which is a flat liquid layer in a glass cell, has been developed. Experimental results have been obtained in the form of space–time temperature distributions for water, glycerol, and a mixture thereof. A dominant mechanism of heat transfer in different stages of heating the liquids under study has been revealed. A mathematical model of the process of free convection is constructed and the space–time temperature distribution is calculated for the case in which water is used as a test object. The results of mathematical simulation correctly describe the experimentally observed character of changes in the thermal field.

Methods and technologies of photonics in endosurgery by D. G. Kochiev; S. A. Naryshkin; O. V. Teodorovich; I. A. Shcherbakov (398-403).
Application of high technologies in surgery and introduction into medical practice of a number of innovations from laser physics and fiber optics has resulted in rapid spread of endoscopic methods of treatment. The development of endosurgery, in turn, promotes the development and introduction into clinical practice of new laser surgical systems, new fiber tools, and high resolution optical systems.

Terahertz spectroscopy of pigmentary skin nevi in vivo by K. I. Zaitsev; N. V. Chernomyrdin; K. G. Kudrin; I. V. Reshetov; S. O. Yurchenko (404-410).
Pigmentary skin nevi are studied in vivo using terahertz pulsed spectroscopy. Dielectric parameters of healthy skin and dysplastic and nondysplastic nevi are reconstructed and analyzed. The fact that complex permittivities of the samples substantially differ in the terahertz spectral range can be used for early noninvasive diagnostics of dysplastic nevi, which are precursors of melanoma (the most dangerous skin cancer). A method is proposed to identify various dysplastic and nondysplastic nevi using the analysis of terahertz dielectric characteristics. It is demonstrated that terahertz pulsed spectroscopy is promising for early noninvasive diagnostics of dysplastic nevi and melanomas of the skin.

An analysis of the results of the structural and spectroscopic studies of 7-Acetoxy-4-(bromomethyl) coumarin (7A4BMC) molecule were performed by FT-IR, FT-Raman, FT-NMR and quantum chemical calculations. The FT-IR and FT-Raman spectra of 7A4BMC were recorded in the 400–4000 and 50–3500 cm–1 region, respectively. The molecular conformations of 7A4BMC were computed at the B3LYP/6-311++G(d,p) level of theory. Molecular structure and spectral calculations were calculated by means of B3LYP with 6-311++G(d,p), cc-pVDZ and cc-pVTZ basis sets. The whole vibrational characteristics of the 7A4BMC molecule are given.

A study of the structure of the ν1(HF) absorption band of the СH3СN…HF complex by E. I. Gromova; E. V. Glazachev; V. P. Bulychev; A. M. Koshevarnikov; K. G. Tokhadze (424-431).
The ν1(HF) absorption band shape of the CH3CN…HF complex is studied in the gas phase at a temperature of 293 K. The spectra of gas mixtures CH3CN/HF are recorded in the region of 4000–3400 cm–1 at a resolution from 0.1 to 0.005 cm–1 with a Bruker IFS-120 HR vacuum Fourier spectrometer in a cell 10 cm in length with wedge-shaped sapphire windows. The procedure used to separate the residual water absorption allows more than ten fine-structure bands to be recorded on the low-frequency wing of the ν1(HF) band. It is shown that the fine structure of the band is formed primarily due to hot transitions from excited states of the low-frequency ν7 librational vibration. Geometrical parameters of the equilibrium nuclear configuration, the binding energy, and the dipole moment of the complex are determined from a sufficiently accurate quantum-chemical calculation. The frequencies and intensities for a number of spectral transitions of this complex are obtained in the harmonic approximation and from variational solutions of anharmonic vibrational problems.

Vibrational spectroscopic studies of L-Alaninium oxalate by N. Balamurugan; C. Charanya; S. Sampathkrishnan (432-440).
An organic crystal of L-Alaninium oxalate single crystal, belongs to the amino acid group, was grown by the slow evaporation solution growth technique at room temperature. The grown crystal had been subjected to single-crystal X-ray diffraction technique and cell parameters of the crystal were determined. The quantitative analysis on the crystal had been carried out using Fourier transform infrared (FTIR) and Fourier transform Raman (FTRaman) spectral measurements. The molecular structures, vibrational wave numbers were calculated using Density Functional Theory method. The calculated Thermodynamic properties were performed.

Spectral sensitization with dyes of core–silver halide shell microsystems by A. V. Tyurin; S. A. Zhukov; V. P. Churashov (441-449).
We have studied spectral sensitization with anionic dyes of core–silver halide shell microsystems cores of which can be either nonsilver or silver halide compounds. Conditions under which dye sensitizers, being adsorbed on cores, remain under silver halide shells after their growing are considered. Comparison of results of sensitometric and low-temperature (T = 77 K) luminescent measurements have shown that these conditions are determined by the charge state of cations of microsystem cores. If the shell contains the same univalent component in its composition as the core does, as in the case in which the core is a silver halide compound, the anionic dye is displaced to the outer surface of the shell. If the core contains a divalent cationic component, as in the case in which the core is a nonsilver compound, the dye remains under the silver halide shell; i.e., it is overgrown by the shell. We have shown that the charge state of core cations affects the character of the core interaction with anionic dyes, which ensures differences in the spectral sensitization of core–silver halide shell microsystems, as well as differences in the dye photoexcitation relaxation in them.

Evolution of the optical properties and morphology of thin metal films during growth and annealing by N. B. Leonov; I. A. Gladskikh; V. A. Polishchuk; T. A. Vartanyan (450-455).
The formation kinetics of an island silver film on a dielectric substrate and changes in the film morphology during heating have been investigated using optical methods. The results obtained are interpreted within a model relating the film optical properties with the shape and size of the nanoparticles forming this film. The proposed interpretation is confirmed by electron microscopy data.

Formation of luminescence centers and nonlinear optical effects in silver-containing glasses under femtosecond laser pulses by D. A. Klyukin; A. I. Sidorov; A. I. Ignatiev; N. V. Nikonorov; M. Silvennoinen; Yu. P. Svirko (456-459).
It is experimentally shown that irradiation of silver-containing silicate glass by IR femtosecond laser pulses leads to generation of free electrons in glass as a result of multiphoton ionization. Free electrons, being captured by charged molecular silver clusters, transform them into the neutral state, as a result of which the luminescence intensity along the laser-pulse track significantly increases. When a laser pulse propagates in glass, cubic nonlinearity dominates in the initial portion of the path, which leads to pulse self-focusing and filamentation. In the final portion of the path, the dominant process is self-defocusing, which is caused by the local decrease in the refractive index as a result of multiphoton generation of free electrons.

A Raman scattering study of the structural ordering in Bi1–x La x FeO3 ceramic ferroelectromagnetics by N. A. Teplyakova; S. V. Titov; I. A. Verbenko; N. V. Sidorov; L. A. Reznichenko (460-466).
Based on Raman spectra, we have studied structural ordering processes in ceramics of ferroelectromagnetics Bi1–x La x FeO3 (x = 0.075–0.20). It has been found that the structure of Bi1–x La x FeO3 is close to the structure of the crystal BiFeO3. However, lines in Raman spectra of Bi1–x La x FeO3 are considerably broadened compared to lines in the Raman spectrum of the BiFeO3 single crystal, which indicates that the structure of solid solutions is much more disordered. In Raman spectra of Bi1–x La x FeO3, in the range of librational vibrations of octahedra as a whole (50–90 cm–1), several groups of lines are observed in frequency ranges 59–69, 72–77, and 86–92 cm–1 (depending on the composition of solid solution). This confirms X-ray data that examined solid solutions are not single-phase. At a La content x = 0.120, Raman lines in the low-frequency spectral range narrow, which indicates that the ordering of structural units in cationic sublattices somewhat increases. Upon an increase in the content of La in the Bi1–x La x FeO3 structure, no unambiguous dependence of parameters of spectral lines is observed. It is likely that this is explained by the fact that, as the value of x increases, the character of the incorporation of La into the structure of the solid solution changes.

Synthesis and characterization of three novel Schiff base compounds: Experimental and theoretical study by P. T. Taslı; A. Bayrakdar; O. O. Karakus; H. H. Kart; Y. Koc (467-484).
In this study, three novel Schiff base compounds such as N-(4-nitrobenzyl)-4-methyl bromo aniline (1a), N-(2,4-dimethoxybenzyl)-4-methyl bromoaniline (2a), SN-((1H-indol-3-yl) methylene)-4- methyl bromoaniline (3a) are synthesized and characterized by using the spectroscopic methods of UV, IR and 1H–NMR. Molecular geometry and spectroscopic properties of synthesized compounds are also analyzed by using ab initio calculation methods based on the density functional theory (DFT) in the ground state. The extensive theoretical and experimental FT–IR and UV–vis spectrometry studies of synthesized compounds are performed. The optimized molecular structure and harmonic vibrational frequencies are studied by using B3LYP/6–311++G(d,p) method. Moreover, electronic structures are investigated by using the time dependent density functional theory (TD–DFT) while the energy changes of the parent compounds are examined in a solvent medium by using the polarizable continuum model (PCM). Additionally, the frontier molecular orbital analysis is performed for the Schiff base compounds. The electronic properties of each compound such as; chemical hardness, chemical softness, ionization potential, electron affinity, electronegativity and chemical potential are investigated by utilizing the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies.

Analytical expressions for velocities of the center of mass and dispersive spreading of optical pulses with a small number of electromagnetic field oscillations in dielectric media have been obtained. For some typical time profiles of input pulses, these expressions are reduced to elementary functions of dispersion characteristics of the medium, central frequency of the pulse, and initial number of oscillations in it. It is shown that the duration of a terahertz pulse of one full-wave oscillation of the field can increase by a factor of $$sqrt 2 $$ when propagating in a dielectric to distances of only three central radiation wavelengths. For pulses of two full-wave oscillations of the field of the near-IR spectral range, the frequency of the zero group dispersion in a dielectric can shift by more than 200 nm.

Dissipative laser bullets in dielectric media containing quantum dots by M. Yu. Gubin; A. Yu. Leksin; M. G. Gladush; S. M. Arakelian; A. V. Prokhorov (497-512).
The formation of three-dimensional spatiotemporal dissipative solitons (laser bullets) in a dense ensemble of two-level quantum dots imbedded into a dielectric host is analyzed theoretically taking into account complex local field corrections. The possibility of satisfying stability conditions for laser bullets in a wide range of concentration and quantum dot size parameters is demonstrated. Substantial increase in dimensions of the found areas of stability when choosing all-dielectric metamaterials as a host medium is revealed.

Numerical simulation of photon density waves in a biophantom with foreign objects by V. L. Kuzmin; A. Yu. Val’kov; A. Oskirko (513-519).
Based on the expression obtained for the scattering intensity in terms of the Bethe–Salpeter equation, the simulation of diffuse photon density wave (DPDW) is implemented in the context of the Monte Carlo method in random media imitating biological tissues in the presence of foreign objects. The DPDW amplitude and phase are calculated as a function of the source–detector distance with explicit allowance for internal reflection effects; the allowance for the Fresnel reflection is necessary for quantitative agreement with measurements. DPDW parameters are calculated for the first time for a biomodel with foreign objects, and optical parameters of the biomodel, as well as spatial parameters of the problem, are estimated for values at which one can visualize an foreign object embedded into the medium.

Semiconductor laser linewidth by E. A. Titov (520-525).
The contribution of quantum fluctuations of the electromagnetic-field amplitude and phase and the medium to the semiconductor laser linewidth is found. It is shown that this contribution increases the linewidth by an order of magnitude in comparison with the contribution of spontaneous radiation.

Self-Q-switching of a loop laser cavity with a self-pumped four-wave phase-conjugate mirror in an active laser medium with the use of a Faraday isolator or a passive Q-switch is studied theoretically. It is found that, in contrast to passive Q-switching of an ordinary cavity, a passive Q-switch in a loop phase-conjugate cavity serves as an auxiliary unit that increases the self-Q-switching efficiency by gain gratings in the active laser medium, since it decreases the difference in the intensities of waves that write a phase-conjugate mirror in the active medium, which is similar to the use of a Faraday isolator. However, the passive Q-switch operates alternating the highly efficient writing of a phase-conjugate mirror in the closed state with the highly efficient generation of a giant laser pulse in the open state, which stabilizes the period of repetitive laser pulses.