C. Madhukar Reddy

Spectroscopic and laser properties of Sm3+ ions doped lithium fluoroborate glasses for efficient visible lasers

The Sm(3+)-doped lead barium zinc lithium fluoroborate (LBZLFB) glasses of composition 20PbO + 5BaO + 5ZnO + 10LiF + (60-x) B(2)O(3) + xSm(2)O(3), (where x=0.1, 0.5, 1.0, 1.5 and 2.0 mol%) have been prepared by conventional melt quenching technique and their structural and spectroscopic behavior were studied and reported. The amorphous nature of these glass samples was confirmed with XRD studies. The FT-IR and FT-Raman spectra reveal that, the glasses contain BO(3), BO(4), non-bridging oxygen and strong OH bonds. The bonding parameters and the oscillator strengths were determined from the absorption spectra. These parameters have been used to obtain the Judd-Ofelt intensity parameters. Using these intensity parameters various radiative and laser properties were predicted. The values of J-O intensity parameters suggested an increase in the degree of symmetry of the local ligand field at Sm(3+) sites. The decay rates for the (4)G(5/2) level of Sm(3+) ions have been measured and are found to be single exponential at lower concentrations (<1.0 mol%) and turn into non-exponential at higher concentrations (≥1.0 mol%), due to energy transfer through cross-relaxation. From the emission characteristic parameters of (4)G(5/2) level, it is concluded that the LBZLFB glasses could be useful for photonic devices like visible lasers, fluorescent display devices and optical amplifiers, operated in the visible region.

Crystal growth and characterization of γ-glycine grown from potassium fluoride for photonic applications.

Single crystals of γ-glycine, an organic nonlinear optical material have been synthesized in the presence of potassium fluoride (KF) by slow evaporation technique at ambient temperature. The size of the grown crystal is up to the dimension of 12 mm×10 mm×8 mm. The γ-phase was confirmed by single crystal X-ray diffraction, powder XRD and the FTIR analysis. Optical absorption spectrum reveals that the grown crystal has good optical transparency in the entire visible region with an energy band gap of 5.09 eV, which is an essential requirement for a nonlinear optical crystal. Thermal stability of the grown γ-glycine crystal was determined using the thermo gravimetric and differential thermal analyses. The NLO activity of γ-glycine was confirmed by the Kurtz powder technique using Nd:YAG laser and the grown crystal exhibits high relative conversion efficiency when compared to potassium dihydrogen phosphate (KDP).

NIR fluorescence studies of Neodymium ions doped sodium fluoroborate glasses for 1.06μm laser applications.

The concentration dependent luminescence properties of Nd(3+) ions doped lead calcium zinc sodium fluoroborate (LCZSFB) glasses were prepared via a melt quenching technique and reported through optical absorption, NIR luminescence and lifetime measurements. The optical transition properties of Nd(3+) ions have been analyzed using Judd-Ofelt theory. The present glasses have high stimulated emission cross - sections, entail that they have high potential laser applications. The decay curves of all the glasses show single exponential behavior. The discrepancy between the experimental and calculated lifetimes of emitting level was ascribed to energy transfer through cross-relaxation. The estimated values of radiative and saturation intensity of (4)F3/2→(4)I11/2 transition indicates the favorable lasing action at 1.06μm.

Green fluorescence of terbium ions in lithium fluoroborate glasses for fibre lasers and display devices

In this paper, for the first time, the visible fluorescence properties, resonance energy transfer mechanism responsible for non-radiative decay rates of 5D4 → 7F5 transition and also quenching of fluorescence intensity of the 5D3 → 7F5 transition of various concentrations of Tb3+ ions in LBZLFB glasses are reported. Optical absorption, fluorescence spectra and quantum efficiencies are measured and analysed. Green fluorescence related to 5D4 → 7F5 (548 nm) transition is registered under excitation of 378 nm of Tb3+ ions. Based on excitation and fluorescence measurements, several spectroscopic parameters for Tb3+ ions are examined as a function of concentration by Judd–Ofelt theory to judge the suitability of studied glasses for display devices and fibre lasers.

Optical absorption and photoluminescence studies of Dy3+: LCZSFB glasses

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

Spectroscopic and laser properties of Sm 3+ ions doped lithium fluoroborate glasses

The present work reports the effect of concentration on photoluminescence properties of Sm³⁺ ions doped lithium fluoroborate (LFB) glasses by using the absorption, emission and decay measurements. The Judd-Ofelt theory has been used to evaluate the three Judd-Ofelt intensity parameters and calculated oscillator strengths. LFBSm glasses exhibit intense reddish-orange emission when excited with 405 nm wavelength. Concentration quenching has been noticed beyond 1.0 mol% of Sm³⁺ ion concentration. The decay curves of ⁴G_5/2 level exhibited single exponential at lower concentrations and turn to non-exponential at higher concentrations. The evaluated radiative properties suggest that the ⁴G_5/2→⁶H_7/2 (602 nm) transition is responsible for reddish - orange luminescence which might be used in the development of visible lasers for photonic applications.