Raman Scattering in Three-Dimensional Photonic Crystals

The optical properties of three-dimensional photonic crystals associated with the form of reflection spectra from their surface (appearance of a forbidden gap in the energy spectrum) and with the specific features of Raman scattering are analyzed. Idealized models of the energy band structure of photonic crystals are studied. Expressions for the group velocity of photons with energy close to the forbidden gap are derived. Experimental results on the Raman scattering in photonic crystals based on artificial opal as well as in fused silica are discussed. Bands due to quantum-size effects (presence of nanoclusters in fused silica and nanoglobules forming the lattice of globular photonic crystals) were manifested in the spectra of inelastic light scattering. It is proposed to use photonic crystals for the creation of sensitive sensors of organic and inorganic substances using modern Raman techniques.     

Stimulated Raman scattering in three-dimensional photonic crystals

The results of experimental studies of stimulated Raman scattering of light (SRS) excited in three-dimensional photonic crystals — synthetic opal matrices infiltrated with Raman active media are presented. It is shown that the SRS threshold in such structures decreases with respect to the SRS threshold in Raman active bulk materials. The influence of the photonic-band structure of the active materials used on the SRS properties is estimated.     

Nonlinear-optical properties of photonic crystals

The results of the experimental study of nonlinear-optical effects in photonic crystals, i.e., synthetic opal matrices and nanocomposites (matrices with voids filled with different nonlinear liquids) are presented. The following nonlinear-optical effects were observed under experimental conditions: the photonic flame effect (PFE), stimulated globular scattering (SGS), and stimulated Raman scattering (SRS). The dependence of these effects on the excitation conditions, nanocomposite refractive index contrast, and sample temperature was studied. PFE lines were detected in the Stokes spectral region. SGS spectra at the temperature of liquid nitrogen were studied.     

Thermally stimulated luminescence origin in LiF crystals irradiated in a reactor at different temperatures

Thermally stimulated luminescence as well as optical absorption and emission spectra have been studied in LiF crystals irradiated in a reactor at different temperatures. It was shown that aggregate colour centres give rise to thermally stimulated luminescence peaks registered below 450°C. Peak at 470°C is observed only in crystals that have been irradiated at standard temperature of the reactor experimental channels. The peak is caused by interaction of dislocations and F centres.     

Ionic conductivity of sodium beta″-alumina

Measurements of the electrical conductivity of Na ß″-alumina show that the low-temperature activation energies are 0.3337 ± 0.0055 eV for MgO stabilized crystals grown at 1700°C, 0.275 ± 0.015 eV for crystals with the same starting composition position grown at 1650°C, and 0.1716 ± 0.0093 eV for crystals stabilized with ZnO and grown at 1700°C. The conductivities of almost all crystals at 500°C were found to be 1.3 ± 0.6 Ω^?1 cm^?1. In addition to the growth conditions, the presence of a dc electric field, the type of electrode material, the type of conducting ion, and the concentration of stabilizing ion are important in determining the electrical conductivity. These factors are believed to affect the nature of the ordering of vacancies in the ß″-aluminas, leading to variations in the activation energy.     

Indirect band gap investigation of orthorhombic single crystals of sulfur

Single crystals of pure and selenium doped orthorhombic sulfur crystal were prepared from carbon disulphide solution. They were investigated at two temperatures (6°C and 85°C) in an optical absorption apparatus. The optical absorption increased with temperature and it was found to be higher for Se doped crystals within the same range of temperatures. The indirect allowed band gap transitions and assisting phonons were observed. Their values were found to shift toward lower energy with increasing temperatures. They are also lower for doped samples. At 6°C, the indirect allowed band gaps are 2.61 eV and 2.56 eV for pure and selenium-doped crystals, respectively. At 85°C, they are 2.44 eV and 2.40 eV for pure and doped crystals, respectively. The phonons associated with the optical transitions could be attributed to the stretching band of S₈ rings.     

On the formation of lamellae during annealing of extended chain crystals of radiation-polymerized trioxane

The structure changes of radiation-polymerized trioxane taking place during annealing have been studied by means of electron microscopy, X-ray small- and wide-angle scattering, and differential thermal analysis. The original fibrillar crystals, supposedly consisting of extended chains, change into lamellar crystals due to annealing at temperatures between 150° and 190°C. Lamella formation can be connected with the appearance of a long period of about 200A which is not observed in the unannealed sample.

During annealing within the same temperature range the X-ray reflections due to the twin structure of the original polytrioxane disappear, whereas the orientation of the fraction with its c-axis parallel to the c-axis of the parent trioxane remains unaltered.

The melting point of the lamellar crystals obtained by annealing is 186°-187°C and, therefore, considerably higher than the melting point (175°C) of crystals grown during cooling of a polytrioxane melt. The equilibrium melting point of an undisturbed extended-chain poly-oxymethylene single crystal must be still higher and may even approach 200°C.

On the basis of the electron-microscopical observations and the X-ray results, it is supposed that the process of lamella formation takes place continuously by reorganization of the whole structure including the already grown lamellae. The rate of this process is the faster the higher the annealing temperature. Some possible mechanisms are discussed but the final reasons for the observed structure changes are not known.     

Spectral and energy characteristics of stimulated globular light scattering

The experimental results on the study of energy and spectral characteristics of stimulated globular scattering (SGS) excited in synthetic opal matrices and nanocomposites on their basis are presented. It is shown that the spectral shift of the first Stokes component (SGS) with respect to the exciting laser line is controlled by the diameter of globules forming the samples under study.     

Brillouin light scattering in LiKSO4 between 20 and 80°C

Elastic constants of LiKSO₄ crystals have been measured at room temperature and over the temperature range 20–80°C by Brillouin scattering. No anomaly has been found near 60°C, in disagreement with the results of a previous Brillouin study which suggested a new phase transition.     

Stimulated Raman scattering of light in artificial opal filled by water

We investigate stimulated scattering of light in globular photonic crystals infiltrated by water. Excitation of stimulated scattering of light is realized using powerful ultrashort (70 ps) laser pulses with an energy of 35 mJ and a frequency repetition of 15 Hz. We use the second-harmonic generation (532 nm) of the master oscillator and amplifier with a wavelength of 1064 nm. The photonic crystals under study are artificial opals filled by water or ethanol. We characterize the sample structures employing an electronic microscope along with the fiber-optics reflectance-spectroscopy technique. Photonic crystals have a stop band near the spectral positions of the exciting line (532 nm) and the first satellite of stimulated Raman scattering of light in water (649 nm). We observe a substantial reduction of the threshold of stimulated Raman scattering of light in water-infiltrated artificial-opal matrices in comparison with that of pure water. Such a reduction is explained as the result of a sharp increase in the photonic density of states near the stop-band edges of investigated photonic crystals. The reduction in the threshold of stimulated Raman scattering of light in water-infiltrated artificial-opal matrices opens up the opportunity to observe stimulated Raman scattering in numerous water media, including water solutions, biological and medical samples, heavy waters, and others.     

Electrical conductivity and thermally stimulated current in the paraelectric phase of (NH4)2SO4

Anomalous variations of d.c. electrical conductivity with temperature are observed in ammonium sulphate single crystals, suggesting a possible phase transition at 150°C. Measurements of thermally stimulated current also support these results. The mechanism of electrical conduction is explained on the basis of studies made on doped and quenched crystals.     

Multifrequency stimulated Raman scattering of light in liquid nitrogen infiltrated into 3D photonic crystals

Spectral characteristics of stimulated Raman scattering at least in synthetic opal matrices infiltrated with liquid nitrogen upon excitation by nanosecond laser pulses are studied. The effect of the stop band position on the generation efficiency of anti-Stokes components of stimulated Raman scattering up to the third order is demonstrated. The excitation threshold of stimulated Raman scattering in liquid nitrogen infiltrated into opals is significantly lower in comparison with the generation in bulk samples.     

Investigation of gallium arsenide single crystals with various crystallographic orientations, after implantation of silicon ions and pulsed photon annealing

The results of experimental investigations of gallium arsenide single crystals with the orientations (100), (311)A, (211)A, (111)A, and (221)A are presented. The crystals were doped with silicon ions on the Iolla-3M setup (ion energy 75 keV, ion beam density 1 μA/cm², implantation dose 1.2×10³ cm⁻²) at room temperature and annealed on the Impul’s-5 setup at 950°C. Raman scattering and low-temperature photoluminescence methods established that the highest electrical activity of the implanted silicon under identical implantation and annealing conditions obtains for (100) and (311)A gallium arsenide. In the process n-type layers are produced. Zh. Tekh. Fiz. 69, 78–82 (May 1999) Deceased.     

Stimulated Raman scattering in light and heavy water under picosecond laser excitation

The spectra of stimulated Raman scattering in ordinary and heavy water under excitation by second harmonic of a picosecond Nd:YAG laser were compared. It was shown that when stimulated Raman scattering is excited in water in cavities of a photonic crystal (synthetic opal matrix constructed of silica nanoglobules) or a photonic glass in the form of close-packed monodimensional millimeter-size amorphous-quartz balls, the efficiency of stimulated Raman scattering increases significantly compared to a uniform liquid medium.     

Diffusion von Protonen (Tritonen) in Eiskristallen

The diffusion coefficient of tritons in ice crystals has been measured at different temperatures between 0°C and ?35°C. The applied method excludes any surface diffusion. The absolute value of the diffusion coefficient at ?7°C was determined as 2·10^?11 cm²/sec (±10%) and the activation energy as 13,5 kcal/mole (±8%). The activation energy of proton (triton)-diffusion is therefore consistent with the activation energy found for the dielectric and mechanical relaxation of protons in ice. The importance of this consistency relative to the diffusion mechanism is discussed.     

Diffusion of iron in lithium niobate: a secondary ion mass spectrometry study

Iron-doped X-cut lithium niobate crystals were prepared by means of thermal diffusion from thin film varying in a systematic way the process parameters such as temperature and diffusion duration. Secondary Ion Mass Spectrometry was exploited to characterize the iron in-depth profiles. The evolution of the composition of the Fe thin film in the range between 600°C and 800°C was studied, and the diffusion coefficient at different temperatures in the range between 900°C and 1050°C and the activation energy of the diffusion process were estimated.     

碳对α的非卢瑟福背散射截面研究

报道了散射角为１７０°±１．５°，α粒子能量在５－９．０ＭｅＶ之间，ｃ的背散射截面的实验测量值；用Ｒ矩阵理论，通过与实验数据拟合，分析、给出了一套能级参数，并计算了能量范围在２－９．０ＭｅＶ，ｃ的背散射截面；讨论了对背散射分析感兴趣的窄而孤立的强共振峰４２５０±１０ＫｅＶ随靶厚、角度的变化关系以及截面变化缓慢的平坦区３．６－４．２０ＭｅＶ，６．４２５－６．７００ＭｅＶ能区的截面值与背散射角度的关系。 关键词：     

Hydrogen accumulation and distribution during the saturation of a VT1-0 titanium alloy by an electrolytic method and from a gas atmosphere

The accumulation, distribution, and thermally stimulated release of hydrogen in a VT1-0 titanium alloy during electrolytic saturation and gas-phase saturation are studied. After electrolytic saturation, a 0.4-μm-thick surface layer consisting of δ hydrides with a binding energy of 108 kJ/mol forms in the alloy. The hydride dissociation after electrolytic saturation in heating occurs in the temperature range 320–370°C. After saturation from a gas atmosphere, δ hydrides with a binding energy of 102 kJ/mol form throughout the alloy volume. The dissociation of the hydrides formed during gas-phase saturation in heating occurs in the temperature range 520–530°C. A further increase in the temperature is accompanied by the transformation of titanium from the α into the β modification. At 690–720°C, the phase transformation is completed, and another hydrogen desorption peak appears in a thermally stimulated hydrogen desorption spectrum.     

Structural evolution,growth mechanism and photoluminescence properties of CuWO4 nanocrystals

Copper tungstate (CuWO₄) crystals were synthesized by the sonochemistry (SC) method, and then, heat treated in a conventional furnace at different temperatures for 1 h. The structural evolution, growth mechanism and photoluminescence (PL) properties of these crystals were thoroughly investigated. X-ray diffraction patterns, micro-Raman spectra and Fourier transformed infrared spectra indicated that crystals heat treated and 100 °C and 200 °C have water molecules in their lattice (copper tungstate dihydrate (CuWO₄·2H₂O) with monoclinic structure), when the crystals are calcinated at 300 °C have the presence of two phase (CuWO₄·2H₂O and CuWO₄), while the others heat treated at 400 °C and 500 °C have a single CuWO₄ triclinic structure. Field emission scanning electron microscopy revealed a change in the morphological features of these crystals with the increase of the heat treatment temperature. Transmission electron microscopy (TEM), high resolution-TEM images and selected area electron diffraction were employed to examine the shape, size and structure of these crystals. Ultraviolet–Visible spectra evidenced a decrease of band gap values with the increase of the temperature, which were correlated with the reduction of intermediary energy levels within the band gap. The intense photoluminescence (PL) emission was detected for the sample heat treat at 300 °C for 1 h, which have a mixture of CuWO₄·2H₂O and CuWO₄ phases. Therefore, there is a synergic effect between the intermediary energy levels arising from these two phases during the electronic transitions responsible for PL emissions.