Jan Cisowski

Optical properties of new aliphatic–aromatic co-polyimides

Abstract Optical transmission of a series of aliphatic–aromatic co-polyimides have been investigated in the range 200–3000 nm. The short wavelength edge of transmission depends on the ratios of diamines (aliphatic to aromatic) and on the type of aliphatic diamine. To obtain the optical parameters the approach proposed by Tauc for amorphous semiconductors has been used, because of the similarity of the absorption edges. The values of pseudogaps were found from 1.01 to above 4 eV, while the Urbach energy changed in the range 75–800 meV. All determined parameters have been found to be related to the influence of the polymer chain structure.

Magnetic susceptibility and luminescence of α-ZnAl2S4 tiospinel doped with chromium

The magnetic susceptibility as well as the optical excitation and luminescence spectra of three samples of α-ZnAl2S4 tiospinel doped with Cr at various concentrations have been measured in the temperature range 77–300 K. The susceptibility has allowed us to estimate the concentration of Cr in the samples studied as lying in the range 0.01–0.06 at.%. Crystal-field theory, including spin–orbit coupling and the trigonal crystal field of the D3d site has been used to fit the optical data. The best-fit parameters of the tiospinel crystal are B20=4800, B40=32500, B43=−28500, F(2)=58800, F(4)=40500 and ξD=300 cm−1. The computational procedure used gives excellent agreement between the experimental and calculated energy levels of the Cr3+ ion in the α-ZnAl2S4 matrix.

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.

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

Randomness of the magnetic ion distribution in dilute magnetic semiconductor epilayers grown by molecular beam epitaxy

Abstract We have applied our extended generalized pair approximation to dilute magnetic semiconductor epilayers grown by molecular beam epitaxy and in this paper we have compared our calculations of the heavy-hole exciton Zeeman splitting with those we measured on Zn1−xMnxSe and those measured by other authors on Cd1−xMnxTe epilayers. It appears that there can be found experimental results, including ours, which exhibit a systematic tendency to lie well below the corresponding theoretical curves based on random distribution. We can clearly attribute this reduced paramagnetic behavior to a non-random distribution of the magnetic ions and we present a way to determine the degree of non-random distribution.

Some aspects of classical and quantum transport in thin films of cadmium arsenide

Abstract We investigated the classical transport properties (the Hall effect and the Hall mobility) and the quantum transport (the Shubnikov-de Haas (SdH) effect) in thin crystalline and amorphous films of Cd3As2. The measurements were performed in high magnetic fields (up to 35 T) at 4.2 K. We found from the SdH effect that the crystalline films are slightly anisotropic, indicating that the investigated structures have a texture, whereas the amorphous films appear to be completely isotropic. Comparison of the Hall data with the SdH data showed some discrepancies between the electron concentrations and mobilities determined by the two methods. The experimental results obtained are discussed on the basis of existing theoretical models for electronic transport in semiconducting thin films.

Characterization of paramagnetic materials by low-temperature magnetization

Abstract A new method of analysis of low-temperature magnetization is presented for materials containing small amounts of randomly distributed magnetic ions. It is shown that, in the case of noninteracting ions, the magnetic field H eq , corresponding to the intercept of extrapolated linear parts of low- and high-field magnetization, does not depend on the magnetic entities concentration x and provides basic information on their magnetic moment, allowing, in turn, for a precise determination of x . It is also shown that, when the magnetic ions start to interact between themselves, H eq shifts towards higher fields and is closely related to the parameter T 0 entering into the modified Brillouin function. The usefulness of the presented method is illustrated by the analysis of results obtained for a number of dilute magnetic semiconductors containing small amounts of transition metal ions.

Influence of temperature on the optical absorption edge in amorphous Zn–P thin films

The effect of temperature (in the range 8 to 300 K) on the fundamental absorption edge of amorphous Zn 32 P 68 thin films have been determined from transmission and reflectivity measurements. Both the Tauc gap, E G , and the Urbach energy, E U , describing the absorption edge, have been shown to follow the Einstein expression for the total energy of a solid. Below 150 K, these two parameters are almost independent of temperature, while in the range 150 to 300 K, they change approximately linearly, but in opposite directions (E G decreases from 1.43 to 1.28 eV, while E U increases from 109 to 145 meV). The coordinates of the temperature independent Urbach focus and a linear dependence between the Tauc gap and the Urbach edge have been found. The observed changes of the optical gap and Urbach energy are discussed and compared with the structural study of the amorphous Zn-P films.

Temperature dependence of the optical absorption edge in amorphous Cd-As and Zn-P thin films

Abstract Temperature dependencies of the optical absorption edge in the amorphous Cd 29 As 71 and Zn 32 P 68 films have been obtained from transmission measurements in the 5–300 K temperature range. The absorption edges for these films were found to follow the Tauc power law with the optical pseudogap E G significant increase with decreasing temperature. A nearly linear dependence of E G on temperature was found in the range from 100 K to about 300 K, while below 100 K the energy gap is almost independent of temperature. For the Cd 29 As 71 film E G was found to be equal to 0.76 eV at 5 K and 0.63 eV at 300 K, while for Zn 32 P 68 film, the energy gap changes from 1.46 to 1.27 eV in the same temperature range. In contrast to E G , the Urbach energy decreases rather slightly with decreasing temperature. The observed change of the optical gap may be attributed to an increase of the mobility gap due to contraction of interatomic distances with decreasing temperature.