A simple theoretical approach based on Kramers-Krönig relations predicts well the dispersion and birefringence of BaLaGa_{3}O_{7} and SrLaGa_{3}O_{7}. In the whole transparency region the birefringence of both compounds is too low to offset dispersion in the process of a second harmonic generation, thus the crystals cannot be made phase matchable. Birefringence of BaLaGa_{3}O_{7} and SrLaGa_{3}O_{7} is stable with respect to the temperature region of 300-550 K. The refractive indices increase linearly at a rate of 2 × 10^{-5} K^{-1} with increasing temperature.
In the paper, some experimental and theoretical results concerning optical bistability in cholesteric liquid crystals are presented. A strong primary laser beam interacted nonlinearly with the material and influenced a second (probe) beam in such a way that its transmitted part exhibited a bistable dependence on the intensity of the first beam. It was observed that such a character may be attributed to the intensity of the outgoing probe wave. The obtained results reflect the symmetry of the sample and are interpreted as second order nonlinearity effects.
The Taguchi approach was applied to optimize optical properties of Dy-Y doped α-SiAlON ceramics produced by spark plasma sintering technique. L'16 experimental design was formed according to orthogonal array. Four different levels were used for each parameter (sintering temperature, holding time, pressure and heating rate). After sintering, the densities of the SiAlON ceramics were measured by the Archimedes method in distilled water. The infrared transmittance behavior was investigated in a wave number range of between 4000 and 1000 cm¯¹ using the Fourier transform infrared. The microstructure characterizations of the samples were carried out using scanning electron microscopy. Optimal sintering conditions were determined by calculated standard analysis. "Higher-is-better" approach was followed to calculate standard analysis. The influences of the sintering parameters on the optical properties and densification of Dy-Y doped α-SiAlON have been analyzed using analysis of variance. It has been concluded that the sintering temperature had greater influence on the density and transparency of Dy-Y doped α-SiAlON ceramics than holding time, pressure and heating rate. Rising sintering temperature to 1850 from 1650°C, at 20 kN pressure with 90 s holding time and 50°C/min heating rate improved the infrared transmittance 49.32% for 0.3 mm sample thickness but higher sintering temperature than 1850°C decreased the transparency of the products.
Cu and Fe doped cadmium sulfide nanoparticles with controllable and relatively narrow size distribution were prepared using a facile and efficient wet chemical route by mixing the reactants in water solvent. It was found that the mixture pH plays an active role in the growth procedure of nanoparticles. Diverse physical properties of the prepared nanoparticles were investigated using UV-vis absorption, photoluminescence spectroscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The average particle size of samples was estimated to be about 5 nm by using transmission electron microscopy measurement. The pH optimization study implies that pH ≈7 would yield an enhancement in photoluminescence intensity. There are two bands in photoluminescence spectra which related to deep and shallow traps.
In the present work we explored the possibility of obtaining Y_2O_3:Eu^{3+} μm-size particles by an ultrasonic spray pyrolysis method. As-prepared sample constitutes of spherical, hollow particles with an average size of 1 to 2 μm. Pure, well crystalline, cubic Y_2O_3 is formed after additional thermal treatment at 800°C for 2 h. A detailed optical investigation has been done with photoluminescence measurements in the energy and time domains. Experimental intensity parameters, transition rates and quantum efficiency of the ^{5}D_0 emission are evaluated on the basis of Judd-Ofelt theory.
This paper describes the all-fiber dual-wavelength thulium ytterbium co-doped fiber laser by using a newly developed octagonal shaped double-clad thulium-ytterbium co-doped fiber as gain medium in conjunction with spatial filtering effect. The thulium ytterbium co-doped fiber laser operates at wavelengths of 1990.64 nm and 1998.92 nm with a signal to noise ratio of more than 34 dB as the 980 nm multimode pump power is increased above a threshold value of 1.5 W. The slope efficiency of the dual-wavelength laser is measured to be around 26.16%, which is comparable with the conventional thulium laser pumped by 800 nm single mode pump.
We apply transformation optics to structures in which the electromagnetic field is confined by highly conducting coatings. The possibility of changing the field propagation direction without perturbation is demonstrated on the example of a waveguide bend. Using this approach it is also possible to reshape a confined structure in order to meet certain external requirements and to redistribute a field in order to obtain desired field distribution. The structure implementation implies replacing a part of given confined structure with a metamaterial designed using the technique of transformation optics. Simplification of structure realization based on using reduced set of material parameters is examined. Our theoretical considerations are confirmed by full wave finite element simulations of a waveguide bend.
Fullerenes, nanotubes, quantum dots are considered as effective sensitizers to modify both the optical, nonlinear optical features, dynamic and polarization characteristics, as well as mechanical and spectral properties of the organic and inorganic materials. The correlation between photorefractivity and photoconductivity was supported and the relation between charge carrier mobility of pure conjugated structures and nanoobjects-doped ones has been revealed. An increase of transmission of nanostructured polarization films was observed. An extension of the nanocomposites applications area is considered.
The paper concentrates on the optical fibre sensors of electric current intensity. The specially elaborated glasses with high values of refractive indices were investigated in the prepared testing stand. The glasses have possessed the refractive index values n in the range 1.6 ≤ n ≤ 2.2. For the glasses the values of the Verdet constants for two waveguides: λ_1 = 635 nm and λ_2 = 1550 nm were determined. The obtained results showed that the elaborated on the base of new glasses optical fibres are much more sensitive on the action of magnetic field than the silica fibres.
In the article the cooperative energy transfer in GeO₂-GaO-BaO glass system doped with Yb^{3+}/Tb^{3+} under 980 nm laser diode excitation was investigated. The influence of Tb^{3+} concentration on the luminescent properties was determined. Measured strong luminescence at 489, 543, 586, 621 corresponds to ⁵D₄ → ⁷F_{J} (J = 6, 4, 3) transitions and luminescence at 381, 415, 435 nm results from ⁵D₃, ⁵G₆ → ⁷F_{J} (J = 6, 5, 4) transitions. Mechanism and energy diagram involved in observed emission were discussed. The highest upconversion emission intensity was obtained in the germanate glass doped with 0.7Yb₂O₃/0.7Tb₂O₃.
We theoretically investigate the feasibility of nonreciprocal light propagation by using the unique features of quasiperiodic one-dimensional photonic crystals. The intrinsic spatial asymmetry of the Fibonacci sequence leads to strong non-reciprocal electric field distribution, so the nonlinear transmission becomes sensitive to the propagation direction. In this work we emphasise on bistability and all optical switching where the switching threshold for one propagation direction is lower than that for the other. In addition we demonstrate that this structure exhibits high transmission due to the existence of high transmission resonances in its linear transmission spectrum, and these features allow creating an all-optical diode.
In this article there are presented the developments on the crystal growth by the Czochralski method of fluoride laser materials at the Center for Lasers and Applications from Institute of Nuclear and Energy Research, IPEN, Brazil. A brief report of the Czochralski furnace preparation for fluorides growth regarding to its construction materials, influence of the heating assemblies in the thermal profiles and the benefits of using a suitable atmosphere is provided. Moreover, to demonstrate the importance of this technique to the advances on laser systems over the last years there are described the specific growth conditions established to obtain fluoride crystals with suitable properties for practical application as laser hosts. LiREF_4 (RE = rare earth) scheelite crystals have been studied to compare LiYF_4 (YLF) with its isomorphs, including solid solutions of the type-LiY_{1-x}Ln_{x}F_4 (Ln = Gd or Lu) and LiGd_{1-x}Lu_{x}F_4, relating to their optical quality, spectroscopic and laser properties. Some results regarding the development of new laser hosts of these materials doped with Nd, Er, Pr and co-doped Yb, Nd and Tm are also presented. The growth particularities of transition metals doped fluoride crystals such as BaLiF_3:TM (TM = Ni and Co) and LiSrAlF_6:Cr are also reported.
In this work we examined the possibility of fabricating the metamaterial in a relatively simple way. Our idea was to use the three-component mixture of ingredients, where one of them is responsible for the negative permeability μ(ω) of hypothetical metamaterial, while the other two cause the negative value of effective permittivity ε(ω). In our previous work, we considered Hg_{1-x}Cd_xTe semiconductor compound as one of the ingredients of mixture. As fabrication of the Hg_{1-x}Cd_xTe is related to using mercury which is very poisoning, we tried to exclude this material. In the work we proved by numerical simulations the possibility of substituting mercury cadmium telluride by Pb_{1-x}Sn_xTe. We have shown by computer simulations that by the proper fitting of the parameters, e.g. the radius of nanoparticles, their magnetic moments, the relative concentration of ingredients, etc., it is possible to obtain the metamaterial with negative refraction index in a relatively broad range of temperatures and magnetic fields. The last seems to be very promising in terms of practical applications of metamaterials.
The authors of the presented paper deal with investigations concerning applications of the optical fiber sensor of the magnetic field in electric DC engines with permanent magnets. The aim of the sensor is to measure the state of magnetization of permanent magnets (basing on the measurements of magnetic field induction). The knowledge of the state of magnetization helps to decide whether permanent magnets need to be additionally magnetized in order to prevent damages of the whole engine. This can be done automatically, even when the engine is running. For the purpose the Faraday magnetooptic effect is used. The presented investigations concern an optical fiber sensor of the magnetic field provided with a glass rod characterized a high value of the Verdet constant as the sensing element. Thanks to the application of optical fibers the connection of the sensor head with the whole measuring system is constructed of insulating material without using of electrical connections.
The paper deals with the optical fibre current sensor based on new optical fibre made of glass with a high value of refractive index. This kind of glass was developed to meet the requirements of these optical fibres. The aim of investigations was to develop a new optical fibre with adequate magneto-optical properties and a relatively weak linear birefringence resulting from the process of its production. These features are of essential importance for optical fibre current sensors. The results of investigations concerning such optical fibres have been presented, displaying satisfactory magneto-optical properties, as well as only low linear birefringence induced by stresses arising in the course of their manufacturing.
Optical fibers may be applied in the technique of measuring electric current, particularly as so-called optical current transducers. They are small in size, cheap, light and safe. Their sensitivity, however, connected with the Faraday effect, is rather poor, and they are also susceptible to considerable disturbances (deformations of the fibers). Their sensitivity can be increased by lengthening the path of effect, but this involves also an increase of noise and greater fluctuations of the measured signal due to changes of internal stresses induced by external factors. These negative phenomena can be reduced by applying fibers less sensitive to deformations. The author supposes that photonic crystal fiber with a glass core may display such properties. Orifices in the cladding can to some extent prevent the propagation of deformations from outside the core, and thus decrease the birefringence of the fiber induced by elastooptic effects. The paper presents preliminary measurements of typical photonic crystal fiber exposed to mechanical vibrations.
In the article effect of temperature on the cooperative energy transfer in germanate glass co-doped with $Yb^{3+}/Tb^{3+}$ under 976 nm laser diode pumping was investigated. The optimization of $Tb^{3+}$ concentration on the upconversion luminescence was determined. Strong luminescence at 489, 543, 586, 621 nm corresponding to $^{5}D_{4} → ^{7}F_{J}$ (J = 6,4,3) transitions and luminescence at 381, 415, 435 nm resulting from $^{5}D_{3}, ^{5}G_6 → ^{7}F_{J}$ (J=6,5,4) transitions were presented. The highest upconversion emission intensity was obtained in glass co-doped with $0.7Yb_{2}O_{3}/0.7Tb_{2}O_{3}$ (mol%). The effect of temperature on the luminescent properties of germanate glass in the range of 5-250°C indicates the presence of competing phenomena: an increase in the effective absorption cross-section of $Yb^{3+}$ ions donor as a function of temperature and migration of energy between pairs of ions $Yb^{3+}-Yb^{3+}$ and of multiphonon excitation levels $^{7}F_{J}$.
The goal of this work was to investigate the spectroscopic properties of Pr^{3+} ions (of a comparable concentration of the order of 0.2 mol/dm^3) embedded in the tellurite glass matrix, i.e. TeO_2-WO_3-PbO modified with lanthanum and lutetium oxides. The difference is that the last components of both glasses provide ions which are optically inactive within the 4f shell, since this shell is completely empty for La^{3+} ion and completely filled for Lu^{3+} ion. The absorption and fluorescence spectra of Pr^{3+} doped in tellurite glass has been recorded and analyzed in terms of the Judd-Ofelt theory. The studies of the glasses comprised ellipsometric, spectrophotometric and photoluminescence measurements. The ellipsometric studies yield the refraction index dispersion which appears to be quite similar for all the studied glasses. From the spectrophotometric measurements, the absorption spectra have been obtained which, for Pr^{3+}-doped samples, have been analyzed in terms of the Judd-Ofelt theory. Finally, the photoluminescence studies demonstrate a clear visible emission from ^3P_0 level to lower-lying states of Pr^{3+} ion.
Temporal and spatial distribution of temperature field was studied in operating acousto-optic devices on base of large-size paratellurite crystals. The study was carried out in real time by means of thermal imaging technique. Dynamics of heat release in a hot deflector and a hot tunable filter was examined at different frequencies and driving electric power levels applied to piezoelectric transducers. The study was also based on measurements of standing wave ratio and analysis of the Smith charts.
The paper presents investigations concerning the analysis of photonic structures with grating couplers. In the paper basic theoretically information on photonic structures with grating couplers is presented. The results of numerical investigations on photonic structures with grating couplers are discussed, too. Investigations show an essential influence of the geometrical parameters of grating couplers on the effectiveness of the input and output of optic power into and out of this photonic structure. In the paper the selected results of experimental realizations of photonic structures with grating couplers based on zinc oxide ZnO are presented.
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