Manuela Reben

Voids in mixed-cation silicate glasses: Studies by positron annihilation lifetime and Fourier transform infrared spectroscopies ☆

PALS in comparison with FTIR studies have been applied to investigate the structure of different oxide glasses. Three components of the positron lifetime τ (τ1 para- and τ3 ortho-positronium and τ2 intermediate lifetime component) and their intensities were obtained. The results of the calculation of mean values of positron lifetimes for the investigated glasses showed the existence of a long-living component on the positron annihilation lifetime spectra. From the Tao-Eldrup formula we can estimate the size of free volume. On the basis of the measurements we can conclude that the size and fraction of free volume reaches the biggest value for the fused silica glass. The degree of network polymerisation increases void size.

Changes of refractive index of tellurite glass

The paper presents the way that colour can serve solving the problem of calibration points indexing in a camera geometrical calibration process. We propose a technique in which indexes of calibration points in a black-and-white chessboard are represented as sets of colour regions in the neighbourhood of calibration points. We provide some general rules for designing a colour calibration chessboard and provide a method of calibration image analysis. We show that this approach leads to obtaining better results than in the case of widely used methods employing information about already indexed points to compute indexes. We also report constraints concerning the technique. Nowadays we are witnessing an increasing need for camera geometrical calibration systems. They are vital for such applications as 3D modelling, 3D reconstruction, assembly control systems, etc. Wherever possible, calibration objects placed in the scene are used in a camera geometrical calibration process. This approach significantly increases accuracy of calibration results and makes the calibration data extraction process easier and universal. There are many geometrical camera calibration techniques for a known calibration scene [1]. A great number of them use as an input calibration points which are localised and indexed in the scene. In this paper we propose the technique of calibration points indexing which uses a colour chessboard. The presented technique was developed by solving problems we encountered during experiments with our earlier methods of camera calibration scene analysis [2]-[3]. In particular, the proposed technique increases the number of indexed points points in case of local lack of calibration points detection. At the beginning of the paper we present a way of designing a chessboard pattern. Then we describe a calibration point indexing method, and finally we show experimental results. A black-and-white chessboard is widely used in order to obtain sub-pixel accuracy of calibration points localisation [1]. Calibration points are defined as corners of chessboard squares. Assuming the availability of rough localisation of these points, the points can be indexed. Noting that differences in distances between neighbouring points in calibration scene images differ slightly, one of the local searching methods can be employed (e.g. [2]). Methods of this type search for a calibration point to be indexed, using a window of a certain size. The position of the window is determined by a vector representing the distance between two previously indexed points in the same row or column. However, experiments show that this approach has its disadvantages, as described below. * E-mail: A.Nowakowski@ire.pw.edu.pl Firstly, there is a danger of omitting some points during indexing in case of local lack of calibration points detection in a neighbourhood (e.g. caused by the presence of non-homogeneous light in the calibration scene). A particularly unfavourable situation is when the local lack of detection effects in the appearance of separated regions of detected calibration points. It is worth saying that such situations are likely to happen for calibration points situated near image borders. Such points are very important for the analysis of optical nonlinearities, and a lack of them can significantly influence the accuracy of distortion modelling. Secondly, such methods may give wrong results in the case of optical distortion with strong nonlinearities when getting information about the neighbouring index is not an easy task. Beside this, the methods are very sensitive to a single false localisation of a calibration point. Such a single false localisation can even result in false indexing of a big set of calibration points. To avoid the above-mentioned problems, we propose using a black-and-white chessboard which contains the coded index of a calibration point in the form of colour squares situated in the nearest neighbourhood of each point. The index of a certain calibration point is determined by colours of four nearest neighbouring squares (Fig.1). An order of squares in such foursome is important. Because the size of a colour square is determined only by the possibility of correct colour detection, the size of a colour square can be smaller than the size of a black or white square. The larger size of a black or white square is determined by the requirements of the exact localisation step which follows the indexing of calibration points [3]. In this step, edge information is extracted from a blackand-white chessboard. This edge information needs larger Artur Nowakowski, Wladyslaw Skarbek Institute of Radioelectronics, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warszawa, A.Nowakowski@ire.pw.edu.pl Received February 10, 2009; accepted March 27, 2009; published March 31, 2009 http://www.photonics.pl/PLP

Influence of lanthanum on structural and magneto-optic properties of diamagnetic glasses of the TeO2–WO3–PbO system

This paper is focused on the design, fabrication and characterization of tellurite glass of composition TeO2–WO3–PbO in terms of La2O3 addition. The effect of La2O3 on the structure of the obtained glasses has been investigated by means of spectrophotometric and ellipsometric measurements in the UV-Vis-NIR spectral region and then relevant optical parameters have been calculated. The DC magnetic susceptibility study has been used to investigate the influence of lanthanum ion (La3+) on the structural and magnetic properties of the investigated glass system. Based on DTA, PALS and Raman studies, it can be stated that modification of the basic structural units with La3+ ions, namely the TeO4 trigonal bipyramid (tbp) and the TeO3 trigonal pyramid (tp), both having a lone pair of electrons occupying one of the equatorial positions, affect the magnetic properties of these glasses.

Influence of fluorine on thermal properties of lead oxyfluoride glass

Oxyfluoride glasses are the basic materials for obtaining transparent glass–ceramic (TGC) which can be used in a wide range of optoelectronics devices such as: amplifiers, up-conversion, telescopes, laser sources. Oxyfluoride TGC is obtained by the control heat treatment of the parent glass due to low phonon nanocrystalline phases. The oxyfluoride glasses from the sodium–lead–silica system were the object of investigation. The influence of fluoride content on the thermal properties of glasses was analyzed. Thermal characteristics of glasses like the transition temperature Tg, the temperature for the crystallization onset Tx, and the maximum crystallization temperature Tc, thermal stability parameter were determined by DTA/DSC method. The linear expansion coefficients of oxyfluoride glasses as a function of temperature were measured using a thermo-mechanical analyzer (TMA 7 Perkin-Elmer). The effect of crystallization on the thermal expansion coefficient and softening temperature Ts was found.

Spectroscopic properties of the Pr3+ ion in TeO2-WO3-PbO-La2O3 and TeO2-WO3-PbO-Lu2O3 glasses

The goal of this work was to investigate the spectroscopic properties of Pr3+ ions, embedded in two different tellurite glass matrices, TeO2-WO3-PbO-La2O3 and TeO2-WO3-PbO-Lu2O3. The absorption and fluorescence spectra have been recorded and analyzed in terms of the Judd-Ofelt theory along with the luminescence decay of the 3P0 and 1D2 levels of the Pr3+ ion. The spectroscopic studies were completed with ellipsometric measurements providing the dispersion relation of the refractive index of the investigated glasses.

Spectroscopic properties of rare earth ions in tellurite glass

The paper presents the way that colour can serve solving the problem of calibration points indexing in a camera geometrical calibration process. We propose a technique in which indexes of calibration points in a black-and-white chessboard are represented as sets of colour regions in the neighbourhood of calibration points. We provide some general rules for designing a colour calibration chessboard and provide a method of calibration image analysis. We show that this approach leads to obtaining better results than in the case of widely used methods employing information about already indexed points to compute indexes. We also report constraints concerning the technique. Nowadays we are witnessing an increasing need for camera geometrical calibration systems. They are vital for such applications as 3D modelling, 3D reconstruction, assembly control systems, etc. Wherever possible, calibration objects placed in the scene are used in a camera geometrical calibration process. This approach significantly increases accuracy of calibration results and makes the calibration data extraction process easier and universal. There are many geometrical camera calibration techniques for a known calibration scene [1]. A great number of them use as an input calibration points which are localised and indexed in the scene. In this paper we propose the technique of calibration points indexing which uses a colour chessboard. The presented technique was developed by solving problems we encountered during experiments with our earlier methods of camera calibration scene analysis [2]-[3]. In particular, the proposed technique increases the number of indexed points points in case of local lack of calibration points detection. At the beginning of the paper we present a way of designing a chessboard pattern. Then we describe a calibration point indexing method, and finally we show experimental results. A black-and-white chessboard is widely used in order to obtain sub-pixel accuracy of calibration points localisation [1]. Calibration points are defined as corners of chessboard squares. Assuming the availability of rough localisation of these points, the points can be indexed. Noting that differences in distances between neighbouring points in calibration scene images differ slightly, one of the local searching methods can be employed (e.g. [2]). Methods of this type search for a calibration point to be indexed, using a window of a certain size. The position of the window is determined by a vector representing the distance between two previously indexed points in the same row or column. However, experiments show that this approach has its disadvantages, as described below. * E-mail: A.Nowakowski@ire.pw.edu.pl Firstly, there is a danger of omitting some points during indexing in case of local lack of calibration points detection in a neighbourhood (e.g. caused by the presence of non-homogeneous light in the calibration scene). A particularly unfavourable situation is when the local lack of detection effects in the appearance of separated regions of detected calibration points. It is worth saying that such situations are likely to happen for calibration points situated near image borders. Such points are very important for the analysis of optical nonlinearities, and a lack of them can significantly influence the accuracy of distortion modelling. Secondly, such methods may give wrong results in the case of optical distortion with strong nonlinearities when getting information about the neighbouring index is not an easy task. Beside this, the methods are very sensitive to a single false localisation of a calibration point. Such a single false localisation can even result in false indexing of a big set of calibration points. To avoid the above-mentioned problems, we propose using a black-and-white chessboard which contains the coded index of a calibration point in the form of colour squares situated in the nearest neighbourhood of each point. The index of a certain calibration point is determined by colours of four nearest neighbouring squares (Fig.1). An order of squares in such foursome is important. Because the size of a colour square is determined only by the possibility of correct colour detection, the size of a colour square can be smaller than the size of a black or white square. The larger size of a black or white square is determined by the requirements of the exact localisation step which follows the indexing of calibration points [3]. In this step, edge information is extracted from a blackand-white chessboard. This edge information needs larger Artur Nowakowski, Wladyslaw Skarbek Institute of Radioelectronics, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warszawa, A.Nowakowski@ire.pw.edu.pl Received February 10, 2009; accepted March 27, 2009; published March 31, 2009 http://www.photonics.pl/PLP

Tellurite glasses for optical fibre fabrication

Technology of tellurite glasses from the TeO2-WO3-PbO-La2O3 has been investigated. The effect of lanthanum oxide content on tendency to the crystallization of glassy matrix has been studied. Differential thermal analysis DTA/DSC, XRD measurement have been considered in term of lanthanum oxide influence. The refractive indices (n) for series of glass compositions with various La2O3 contents compared with glass without La2O3 addition has been measured. From obtain results it has been stated that the refractive index slightly increases with the addition of the lanthanum oxides in all glass of compositions. Double crucible drawing technique was applied to drown tellurite optical fibre with high numerical aperture (0.8).

Thermal study of the influence of chemical composition on CRT glass crystallization

The influence of alumina oxide on the crystallization of silica–strontium–barium glass from cathode ray tube (CRT) was studied by means of thermal analysis. Thermal characteristics of glasses such as the transition temperature Tg, the crystallization temperature Tc and thermal stability parameter were determined by DTA/DSC method. The crystallization ability of the obtained glasses was also determined independently by the gradient furnace technique. The crystalline phase was determined by the X-ray diffractometry. The microstructure of the samples was studied by SEM technique. The linear expansion coefficients of glasses as a function of temperature were measured. Analysis of the local atomic interactions in the structure of glasses was used to explain the course of the crystallization. The effect of Al2O3 content on the CRT glass composition was studied by FTIR and solid-state 19F MAS–NMR spectroscopy.

Photoluminescent properties of rare-earth ions in TeO2-WO3-PbO-La2O3 glasses

The tellurite-tungstate glasses containing small amounts of rare-earth ions have been studied experimentally at 77 and 293 K using spectroscopic methods. The photoluminescence (PL) studies reveal the emission of efficient green-yellow light from Tb³⁺ ions and red light from Eu³⁺ ions. The Judd-Ofelt intensity parameters have been derived for Nd³⁺ and Er³⁺ ions from the absorption spectra and they have used to calculate the radiative lifetimes and branching ratios. The quantum efficiency η = 0.95 of the ⁴F_3/2 level of Nd³⁺ ion is higher than the typical value of other tellurite-based glasses. For Er³⁺ ions, PL originating from the ⁴S_3/2,⁴I_11/2 and ⁴I_13/2 levels has been observed and the luminescence decay of the first two levels has been found to be governed by radiative transitions and multiphonon relaxation involving the highest energy of Te-O vibrations.

Influence of chemcial composition on properties of tellurite glass Yb3+ doped

The goal of this work was to investigate the influence of ZnO on physico-chemical properties of tellurite glasses of the TeO2-ZnO-PbO-La2O3 system, including those doped with Yb3+. The effect of glass crystallization on the thermal stability and crystallizing phases formed upon the heat treatment were investigated by DTA/DSC/, XRD and microscopic methods. The spectral dependence of ellipsometric angles of the tellurite glass samples, have been studied. The influence of ZnO and Yb3+ ion, onto changes of refractive index of tellurite glass (without RE admixture) were examined. The optical measurements were conducted on Woollam M2000 spectroscopic ellipsometer, in spectral range of 190-1700 nm. Based on obtained results it can be concluded, that admixtures of ZnO have the most considerable influence on thermal stability tellurite glasses raise.