卷 121, 编号 1 (2016)

The laser-induced breakdown spectroscopy (LIBS) and surface morphology of Titanium (Ti) plasma as a function of laser irradiance have been investigated under ambient environment of argon at fixed pressure of 50 Torr. Ablation was performed by employing Q-switched Nd:YAG laser pulses (λ ≈ 1064 nm, τ ≈ 10 ns, repetition rate ≈ 10 Hz). Ti targets were exposed to various laser intensities ranging from 6 to 50 GW/cm². LIBS analysis has been employed for the investigation of plasma parameters. Scanning Electron Microscope (SEM) analysis was employed for investigation of surface morphology. Ablation depth was measured by optical microscopy technique. It was observed that both plasma parameters, i.e., excitation temperature and electron density have been significantly influenced by laser irradiance. It is observed that with increasing laser irradiance up to 13 GW/cm², the electron temperature decreases whereas number density significantly increases and attains its maxima. Afterwards by increasing irradiance electron temperature increases, attains its maxima and a decrease in electron number density is observed at irradiance of 19 GW/cm². Further increase in irradiance causes saturation with insignificant changes in both electron temperature and electron number density. This saturation in both excitation temperature and electron number density is explainable on the basis of self-sustaining regime. SEM micrographs reveal the ripple and coneformation at the boundaries of ablated region of Ti. The height of cones as well as the ablation depth is maximum at irradiance of 13 GW/cm² whereas electron number density is also maximum. The maximum electron number density is considered to be responsible for maximum ablation as well as mass removal. A strong correlation between plasma parameters and surface morphology is established.

We show that the contour of an absorption band of a thin layer of a liquid or a film of a solid compound deposited onto a substrate can be strongly distorted as a result of the reflection from the specimen surface or the interface with the substrate if the refractive index of the compound under study changes sharply in the range of the absorption band. We consider the theory of this phenomenon and ways of taking it into account in studies of the absorption spectra of films, liquids, and adsorbed molecules.

The polarized Raman spectra of SrB₄O₇ (SBO) single crystals are studied in detail in the temperature range of 300–1273 K. The TO, LO, and IO phonon lines of A₁, A₂, B₁, and B₂ symmetries of rhombic SBO at 300 K are identified. The behavior of the Raman spectra of SBO crystals is studied upon heating up to their melting. The relation of Raman spectra with the structure of boron–oxygen fragments, as well as the transformation of spectra in the process of melting of SBO crystals, is discussed.

From the concentration dependence of the widths and intensities of Raman lines and from the patterns of photoinduced light scattering, it is found that the mechanism of incorporation of Zn²⁺ cations into the LiNbO₃ crystal structure changes with increasing concentration of zinc in the melt, which leads to an abrupt anisotropic expansion of oxygen octahedra along the polar axis. In this case, the number of kinks in the concentration dependence of linewidths (5) considerably exceeds the number of concentration threshold (2) known from the literature. It is shown that B³⁺ ions almost do not enter the cationic sublattice of the LiNbO₃ crystal but changes the melt structure, so that the LiNbO₃:B crystal is characterized by a high structural and optical homogeneity and a low photorefractive effect.

Optical and electrical properties of cyanoethyl ether of polyvinyl alcohol with filling of barium titanate BaTiO₃ modified by shungite carbon nanoparticles are studied. It is found that the modification affects the diffuse reflectance spectra and dispersion characteristics of the impedance components due to a change in the nature of interfacial interactions in the system. The values of the forbidden band width for various modifier and filler concentrations are determined.

We have investigated the laser-excited photoluminescence spectra of powder and aqueous solution threonine. The spectral ranges of the photoluminescence and its intensity maxima have been determined. We have measured the spectral dependence of the molar extinction coefficient of an aqueous solution of threonine. Using quantum-chemical methods, we have calculated the electron absorption spectrum, the dipole moment, and the distributions of charges on individual atoms of the threonine molecule. The calculated electron absorption spectrum has been compared with experiment.

LEDs with the advantage of high luminous efficacy and long life time show the potential of replacing traditional luminaire. Most commercial white LED light sources use blue or ultraviolet chip coated with emitting phosphor, but the sensitivity and instability of such phosphors has become a big issue. The typical RGB-LED by using individual chips has the problem of spatial separation and insufficient spectral overlap which leads to low CRI. This study suggests a novel and high-efficiency design of fiber optical optocoupler to synthesize four colors emitted by separate LEDs to provide the ideal light sources by adjusting the individual LEDs separately. By choosing different colored light to be synthesized, this optocoupler can be used as light sources which can be highly controlled to offer the best lighting conditions. Compared with other widely used commercial LED sources, this new design of light sources can be used in special experiments which require multi-spectral light.

The frequency–time correlation of inhomogeneous broadening on different transitions in a threelevel resonant medium in the presence of external spatially nonuniform electric fields is considered. It is shown that, under a certain relationship between the magnitudes of gradients of external nonuniform electric fields acting at different moments of time, it is possible to control the magnitude of the frequency–time correlation on different frequency transitions. An increase in the frequency–time correlation coefficient with certain strengths of external spatially nonuniform electric fields leads to the recovery of the phase memory of the system and an increase in the stimulated photon echo intensity.

Theoretical analysis of the spatial, noise, and energy characteristics of an amplifier has been performed in the mode of spectral and time selection using subnanosecond stimulated Raman Scattering gain of weak echo signals in crystalline active media that are known for high (up to 10^–1 cm/MW) gain coefficients. The possibility to reach high gain values has been demonstrated for weak signals from objects at acceptable angular sizes of the field of vision of an amplifier. To provide a signal-to-noise ratio that exceeds unity over the entire field of vision, the number of photons at the input to an amplifier that is required has to exceed the number of its resolution elements. Accurate determination of the possibilities of recording of weak echo signals and quality of images of targets that are obtained using amplifiers under stimulated Raman Scattering requires additional special experiments.

We study the specific features of the perturbation dynamics of a wave packet in a Gires–Tournois interferometer. We obtain a dispersion relationship that relates the perturbation parameters to the parameters of the structure and pump wave, the analytical expressions for the gain increment of a harmonic perturbation and other important characteristics that determine the dynamics of the modulation instability of the reflected wave. Based on numerical simulation, we plot the dependences of the dispersion and nonlinearity parameters and the gain increment on the spacing between the interferometer mirrors, the angle of incidence of the radiation onto the mirrors, and the radiation intensity.

Indicatrices of the light scattering on homogeneous nanoparticles with radii of r₀ = 50, 75, and 100 nm and on double-layer nanoparticles with core radii of r₀ = 40, 65, and 90 nm and a shell thickness of Δ_r = 10 nm are calculated numerically for light wavelengths of λ = 300, 560, and 1000 nm. Metals Ti, Ni, and Zn and their oxides, TiO₂, NiO, and ZnO, were used as materials for homogeneous nanoparticles. The same metals and their oxides were used, respectively, as materials for the core and the shell of the double-layer nanoparticles. It is shown that, in comparison with the pure metal or pure oxide dielectric nanoparticles, the presence of the oxide shell on the titanium and nickel cores leads to a significant decrease in the backscattering for λ = 300 nm.

The results of a theoretical study of the transformation properties of thin dynamic χ⁽²⁾ holograms for all frequency mixing versions are generalized, and a general pattern of transformations of reconstructed images (recorded and read at different frequencies) is developed. The principles of ray geometric construction of reconstructed images are determined. The theory of thin dynamic χ⁽²⁾ holograms is extended to the range of third-order aberrations.

We investigate the kinetics of photodarkening and recording of holographic diffraction gratings in amorphous As₄S₃Se₃ thin-film structures doped with tin (Sn) in concentrations of 0–10 at %. It is established that an increase in the Sn concentration leads to a decrease in the photodarkening rate and degree. The photodarkening kinetics is approximated by a stretched exponential function. It is found that an increase in the Sn concentration leads to a decrease in the transmission (photodarkening) variation in the investigated As₄S₃Se₃–Sn films. It is determined that, in the recording of holographic diffraction gratings at a Sn concentration of 3–8 at %, the As₄S₃Se₃–Sn films exhibit the maximum sensitivity and diffraction efficiency of the recorded gratings. It is shown that the dependence of diffraction efficiency on the As₄S₃Se₃ film thickness has the maximum at a film thickness of 4 µm.

On the basis of analyzing the cosine light field with determined analytic expression and the pseudo-inverse method, the object is illuminated by a presetting light field with a determined discrete Fourier transform measurement matrix, and the object image is reconstructed by the pseudo-inverse method. The analytic expression of the algorithm of computational ghost imaging based on discrete Fourier transform measurement matrix is deduced theoretically, and compared with the algorithm of compressive computational ghost imaging based on random measurement matrix. The reconstruction process and the reconstruction error are analyzed. On this basis, the simulation is done to verify the theoretical analysis. When the sampling measurement number is similar to the number of object pixel, the rank of discrete Fourier transform matrix is the same as the one of the random measurement matrix, the PSNR of the reconstruction image of FGI algorithm and PGI algorithm are similar, the reconstruction error of the traditional CGI algorithm is lower than that of reconstruction image based on FGI algorithm and PGI algorithm. As the decreasing of the number of sampling measurement, the PSNR of reconstruction image based on FGI algorithm decreases slowly, and the PSNR of reconstruction image based on PGI algorithm and CGI algorithm decreases sharply. The reconstruction time of FGI algorithm is lower than that of other algorithms and is not affected by the number of sampling measurement. The FGI algorithm can effectively filter out the random white noise through a low-pass filter and realize the reconstruction denoising which has a higher denoising capability than that of the CGI algorithm. The FGI algorithm can improve the reconstruction accuracy and the reconstruction speed of computational ghost imaging.

An algorithm is developed and computer simulation of wind sensing by means of micropulse coherent Doppler lidars (CDLs) in the atmospheric boundary layer is conducted for low values of the signalto- noise (SNR) ratio. The accuracy of lidar wind measurements is studied numerically for parameters of micropulse Stream Line CDLs. Optimal parameters of the measurements and processing data obtained at low SNR, which allow reconstructing vertical profiles of the wind velocity vector with required accuracy within an entire atmospheric boundary layer, are determined.