Nonlinear optical phenomena at the interface with photorefractive crystals

Characteristics of nonlinear optical phenomena in reflection of light at the interface with photorfractive crystals having photovoltaic nonlinearity are studied. it is shown that under total reflection, hysteretic behavior of the reflection coefficient is possible as a function of the incident radiation intensity or the angle of incidence. It is important that previously required threshold intensities are rather low (≤1 W/cm²) in comparison with the known case of reflection from media with Kerr nonlinearity. The present results are of doubtless interest in view of the development of possible devices for controlling laser radiation. Interdepartmental Institute of Advanced Training of Personnel in New Trends in Engineering and Technology at the State Polytechnical Academy of Belarus, 77, Partizanskii Ave., Minsk-107, 220600 Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 915–920, November–December, 1998.     

Device for UV irradiation of blood with a disposable blood flow system

A device for extracorporal irradiation of blood by UV light with λ=300–400 nm is described. A disposable blood flow system with a specially profiled polymer cuvette is proposed. Mixing of blood during irradiation ensures uniform irradiation of blood cells passing through the cuvette, which makes it possible to enhance the healing effect of the procedure. B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 289–292, March–April, 1999.     

A multimode model of a waveguide laser cavity with mirrors of arbitrary radius of curvature

A multimode model is developed to determine optical losses in a waveguide laser cavity of cylindrical symmetry with mirrors of arbitrary radius of curvature. Within the framework of the model, it is possible to vary the parameters of the resonator: waveguide length, distance between the waveguide and mirrors, radius of curvature of the mirrors in a wide range taking account of mutual conversion of up to 10 waveguide modes and 20 modes of free space. The model was applied successfully to determine the optimal geometry of a semiconfocal cavity. A. N. Sevchenko Scientific-Research Institute of Physical Problems, 7 Kurchatov Str., Minsk, 220064, Belarus; e-mail: v.saetchnikov@rfe.bsu.unibel.by. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 779–783, November–December, 1999.     

The width of the rotational contour of vibrational and vibronic bands of complex molecules in the gas phase as a temperature indicator

From the independence of the contour of spectral density of the rotational (orientation) correlation function of a rigid molecular top of arbitrary symmetry on temperature in the frequency scale based on the reduced time of rotational orientation relaxation and from the near independence of the rotational contour of vibrational and vibronic absorption bands of dipole transitions in the same coordinates in a model of “regular diffusion” of the transition oscillator with a classically rotating rigid molecular top, it is suggested that it is possible to use the halfwidth of the contour for estimation of temperatures. Data are presented on the halfwidth of 48 contours of bands of A, B, and C types at this frequency for 12 compounds for a temperature range of from units to 500 degrees of absolute temperature measured experimentally and (for low temperatures) calculated by the quantum theory. Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 312–317, May–June, 1997.     

Formation of a complex nonlinear response in bichromophore solutions

A theoretical investigation of the dynamics of the stimulated emission of solutions of bichoromophores consisting of a donor with a high intersystem crossing probability and an acceptor between which a radiationless inductive-resonant energy transfer is possible is carried out. The complex dynamics of the behavior of the system is demonstrated, which makes it possible to use these chromophore ensembles as multistable devices with a memory of order of the triplet state lifetime. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 353–357, May–June, 1997.     

Study of the profiles of atomic absorption lines in an electrothermal atomizer

Narrow atomic absorption lines of Ba, Cs, Mg, and Tl are recorded in an electrothermal atomizer with a graphite tube furnace by the intracavity laser spectroscopy method. The conditions of applicability of this laser absorption method for reducing the observed profiles of spectral lines to the true ones are found. Measurement of the integral absorption coefficient has made it possible to determine the absolute number of free atoms of each element in the analyte volume at the maximum of the absorption peak under optimum conditions of atomizer heating. The Voigt parameters are determined from the profiles of absorption lines. Institute of Molecular and Atomic Physics of the National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 27–33, January–February, 1998.     

New analytical possibilities of a steeloscope fitted with a multielement photodetector

It is shown that the use of a multielement photodetector (CCD strip) as an attachment to a steeloscope eliminates the subjectivity of visual analysis, makes it possible to obtain operative information on measurement results, extends the spectral range of the device, and improves the working conditions of analysts. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 284–286, March–April, 1998.     

Influence of optical feedback on macroscopic quantum-noise-induced fluctuations in stimulated RS

Results of an experimental study of optical feedback as a method to suppress quantum-noise-induced macroscopic fluctuations in the emission of stimulated RS are reported. Statistic changes in the energy of Stokes pulses in the linear mode of scattering and those in the amplitudes of solition-like pulses in the nonlinear mode are shown. A decrease in the normal standard deviation of fluctuations is attained for both modes. B. I. Stepanov Institute of Physics of the Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 450–457, July–August, 1997.     

Calculation of the characteristics of a two-mode laser with weakly coulped anisotropic cavities

On the basis of the method of self-consistent waves in lasers with weakly coupled anisotropic cavities we obtained analytical expressions for the spectrum of radiation frequencies and threshold gain coefficients of orthogonally polarized waves in the active part of a coupled cavity for an arbitrary set of anisotropic and other optical elements in its passive part. Belarusian State Polytechnic Academy, 65, F. Skorina Ave., Minsk, 220027, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 262–265, March–April, 1999.     

Induced quasicrystallinity of solutions of organic compounds

Using the method of optical probing, we investigated the effect exerted by the concentration of the substance and the temperature of the solution on the spectral behavior of the difference in the refractive indices of ordinary and extraordinary waves Δn=n_o−n_e of excited solutions of Rhodamine 6G and 3,6-tetramethyldiaminophthalimide in glycerin. We established that laser-excitation-induced quasicrystallinity of the indicated solutions in probing in the fluorescence band, which is characterized by the magnitude of the difference between the refractive indices Δn, increases with increase in the concentration of the substance. This increase in the crystallinity of the system with increase in the concentration of the substance (the activator) is possible up to the instant of the appearance of intermolecular interaction of the molecules. To whom correspondence should be addressed. Reported at the Second International Scientific and Technical Conference on Quantum Electronics, Minsk, November 23–25, 1998. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 672–674, September–October, 1999.     

Special features of the EPR spectroscopy of a system of centers with different relaxation times

We found that the interaction of paramagnetic centers that have different relaxation times differs fundamentally from the interaction of centers having close relaxation times. Simulation showed that in this case there is an anomalous redistribution of the spectral-line intensity from the center to the wings with a virtually preserved distance between extremal points (super-Lorentzian shape of the line), which leads to underestimation of the total intensity recorded. The results obtained make it possible to explain a number of aspects of the radiospectroscopy of carbon materials of practical importance such as the nature of the generally accepted maximum on the curve for the dependence of the total intensity of an EPR signal on the temperature of the heat treatment of organic compounds and the degree of metamorphism of natural coals, the specific features of the effect of oxygen molecules and paramagnetic ions of metals on the EPR spectra of carbon materials, etc. Belarusian State University, 4, F. Skorina Ave., Minsk, 220080 Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 224–229, March–April, 1998.     

Control of the shape and duration of a laser pulse in the case of nonlinear total internal reflection

A nonlinear device based on nonlinear total internal reflection is suggested which provides a more than ten-fold shortening of the laser pulse and smooth variation of the pulse duration due to double reflection from the interface between transparent and absorbing media. Results are presented for the shape and duration of the pulse components that have been reflected and transmitted by the interface. B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., 220072, Minsk, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 325–328, May–June, 1997.     

Photoelectric properties ofp-CuInSe2 thin films obtained by pulsed laser vaporization

Using the method of phase-sensitive detection, we investigated the photoconductivity spectra of polycrystalline p-CuInSe₂ films obtained in vacuum by the method of pulsed laser vaporization of initial single crystals. We show that, in contrast to single crystals, films are characterized by monopolar photoconductivity in the extrinsic and intrinsic regions of optical absorption and by a linear mechanism of recombination of nonequilibrium charge carriers at the intensities of illumination 0–100 mW/cm² in the temperature range 80–300 K. Institute of the Solid-State and Semiconductor Physics, National Academy of Sciences of Belarus, 17, P. Brovka St., Minsk 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii. Vol. 66, No. 1, pp. 138–141, January–February, 1999.     

Applicability of approximate methods of calculation of the frequency-contrast characteristics of aerosol layers within the wavelength range of 0.4–14 μm

The spectral dependences of the optical characteristics governing radiation transfer in scattering media are analyzed within the wavelength range of 0.4–14 μm for three types of aerosols. The wavelength ranges where approximate methods of calculation of frequency-contrast characteristics are applicable are established; the corresponding limitting masses of aerosol particles in a layer per unit of surface area are determined for which approximate methods provide acceptable accuracy. B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 70 F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 419–425 May–June, 1998.     

Influence of isovalent substitutions on absorption spectra of orthoferrities

The role of impurity ions in formation of the optical properties of rare-earth orthoferrites is investigated. Optical spectra of the substituted against unsubstituted orthoferrites are presented. The influence of different isovalent substitutions on the optical absorption of orthoferrites that are promising for magnetooptics is studied. Institute of Solid-State and Semiconductor Physics of the Academy of Sciences of Belarus, 17, P. Brovka St., Minsk, 220072, Belarus. Translated from zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 642–645, September–October, 1997.     

Optical properties of thin anisotropic films of polyethyleneterephthalate in the spectral range of 700–760 cm−1

Using transmission coefficients of anisotropic polyethyleneterphthalate films measured in the range of 700–760 cm⁻¹ the optical functions n(v) and χ(v) are calculated in the film plane and perpendicular to its surface. Its shown that the asymmetric broadenings and shift of the maximum of the absorption band at 727 cm⁻¹ in the case of oblique incidence of p-polarized radiation are due to the influence of optical anisotropy and dispersion. A. A. Kuleshov Mogilev State University, 1, Kosmonavtov Str., Mogilev, 212022, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol 66, No. 3, p. 409–412, May–June, 1999.     

Spectra of the action of photoinduced NH(ND)-rearrangement of cyanosubstituted isobacteriochlorin

Based on the measured spectra of the action of the process of cis-trans-NH(ND)-isomerization of 5-cyano-2,2,8,8,12,13,17, 18-octamethylisobacteriochlorin (H₂-COMiBCh) and its deuteroderivative (D₂-COMiBCh) in polycrystalline matrices of n-octane and r hexale at 4.2 K, it is established that the character of embedding of COMiBCh in the matrices of n-alkanes has a substantial effect on the barrier of dark rearrangement and the rate of photoinduced NH(ND)-rearrangement, while deuteration of the center of a molecule shifts the dynamic equilibrium toward a trans-form in photoexcitation. To whom correspondence should be addressed. Reported at the VIIIth International Conference on Spectroscopy of Porphyrins and Their Analogs, Minsk, September 22–26, 1998. Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70, F. Skorina, Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 4, pp. 555–559, July–August, 1999     

Absorption and fluorescence of 9,10-diiodoanthracene in undegassed solutions

A procedure for producing 9,10-diiodoanthracene that is an alternative to the known procedure is described. The spectra of absorption and fluorescence in hexane, carbon tetrachloride, and polymethylmethacrylate are measured at 22°C. The quantum yield of undegassed liquid solutions in hexane and carbon tetrachloride in excitation at the maximum of the 0←0 band is practically the same and is equal to 0.018. In excitation in shorter-wave vibrational bands, it is different for different solvents and decreases noticeably as the frequency of the exciting light increases. The decrease in the yields is explained by the existence of a fast nonradiative process from hot (Franck-Condon) vibrational S₁-states capable of competing with vibrational relaxation. A possible scenario of this approach is discussed. Institute of Molecular Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 2, pp. 197–200, March–April, 1999.     

Transformation of radiation-induced defects responsible for theF-band of absorption in NaF crystals subjected to irradiation with light and annealing

It has been found that the F-band of optical absorption which is observed in ψ-irradiated NaF crystals consists of three overlapping bands. The band at 345 nm of width 40 nm is independent of the impurity composition of the crystals; it disappears upon exposure to radiation at 345 nm and appears again upon annealing at 460±15 K for 15 min. This band is correlatable in intensity with the superfine structure of an EPR spectrum. The width (65–110 nm) and the spectral position (355–375 nm) of the second band depend on the impurity composition of the crystal. The band of width 90–110 nm at 320–325 nm disappears upon annealing and appears after exposure to light simultaneously with the disappearance of an EPR signal. It is established that the band at 345 nm is caused by quasimolecules based on fluorine atoms, that at 355–375 nm is triggered by F-centers with a different impurity composition near the haloid vacancy, and the band at 320–325 nm owes its appearance to F-centers in a negatively charged state (F′). Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70 F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 849–853, November–December, 1999.     

Effect of sweeping the “instantaneous” lasing frequency on the amplitude-detuning characteristic of a CO2 laser with loss modulation

The influence of changes in the refractive indices of the active medium and the loss modulator on the amplitude-detuning characteristic of a CO₂ laser was theoretically investigated. It is shown that at a comparatively great magnitude of sweeping the “instantaneous” lasing frequency, the magnitude of the laser response increases not only in negative detunings, but also over a wide range of positive detunings. The use of the procedure of changing the magnitude and sign of detuning as well as the range of sweeping and the frequency of modulation makes it possible to realize various periodic and chaotic regimes of lasing, i.e., to exercise control over the time and energy parameters of pulses over a very wide range. B. I. Stepanov Institute of Physics of the Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 318–324, May–June, 1997.