Solvent-casting of Chalcogenide Glasses and Their Applications in Mid-infrared Optics PDF Download

Author: Shanshan Song
Publisher:
ISBN:
Category :
Languages : en
Pages : 264

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Author: Valentina F. Kokorina
Publisher: CRC Press
ISBN: 9780849337857
Category : Technology & Engineering
Languages : en
Pages : 260

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This book explores oxygen-free chalcogenide glasses, the only commercial transparent vitreous materials used for long-wave infrared radiation. The chalcogenides have been the subject of study around the world for many years, and continue to be an important area of research and development in infrared optics. Written by a renowned glass specialist with extensive experience working with chalcogenide glasses, Glasses for Infrared Optics includes discussions of: Chalcogenide glasses - a unique class of vitreous substances Optical properties of chalcogenide glasses Elaboration of commercial glasses Technological basics for manufacturing optical chalcogenide glasses The material presented in Glasses for Infrared Optics is based on research performed at the Vavilov State Optical Institute in Russia. This is the first and only work that reviews every aspect of chalcogenide glasses. The scope of this comprehensive book is unique, and the major portion of this work has never been published before in English.

Author: A. Ray Hilton
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Lin Zhang
Publisher:
ISBN:
Category : Micromachining
Languages : en
Pages : 144

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Precision glass molding (PGM) is being considered as an alternative to traditional methods of manufacturing large-volume, high-quality and low-cost optical components. In this process, glass optics is fabricated by replicating optical features from precision molds to glass at elevated temperature. Chalcogenide glasses are emerging as alternative infrared materials for their wide range infrared transmission, high refractive index and low phonon energy. In addition, chalcogenide glasses can be readily molded into precision optics at elevated temperature, slightly above its glass transition temperature (Tg), which in general is much lower compared to oxide glasses. The primary goal of this research is to evaluate the thermoforming mechanism of chalcogenide glass around Tg and investigate its refractive index change and residual stresses in molded lens in and post PGM. Firstly, a constitutive model is introduced to precisely predict the material behavior in PGM by integrating subroutines into a commercial finite element method (FEM) software. This modeling approach utilizes the Williams-Landel-Ferry (WLF) equation and Tool-Narayanaswamy-Moynihan (TNM) model to describe (shear) stress relaxation and structural relaxation behaviors, respectively. It is predicted that `index drop’ occurred inside the molded prism due to rapid thermal cycling and the cooling rate above Tg can introduce large geometry deviations to the molded optical lens. Secondly, the refractive index variations inside molded lenses are further evaluated by measuring deviation angle through a prism & wavefront changes through molded lens using a Shack-Hartmann wavefront sensor (SHS), while the residual stresses trapped inside the molded lenses are obtained by using a birefringence method. Measured results of the molded infrared lenses combining numerical simulation provide an opportunity for optical manufacturers to achieve a better understanding of the mechanism and optical performance variation of chalcogenide glasses in and post PGM. Upon completion of the aforementioned research, two typical micro IR optics are designed, fabricated and tested, an infrared SHS and a large field-of-view (FOV) microlens array, as demonstrations. A novel fabrication method combining virtual spindle based high-speed single-point diamond milling and PGM process is adopted to fabricate infrared microlens array. The uniqueness of the virtual spindle based single-point diamond milling is that the surface features can be constructed sequentially by spacing the virtual spindle axis at an arbitrary position based on a combination of rotational and transitional motions of the machine tool. After the mold insert is machined, it is employed to replicate the optical profile onto chalcogenide glass. On the other hand, an infrared compound-eye system consisting of 3×3 channels for a FOV of 48°×48° is developed. The freeform microlens array on a flat surface is utilized to steer and focus the incident light from all three dimensions (3D) to a two-dimension (2D) infrared imager. Using raytracing, the profiles of the freeform microlenses of each channel are optimized to obtain the best imaging performance. To avoid crosstalk among adjacent channels, a micro aperture array fabricated by 3D printing is mounted between the microlens array and IR imager. The imaging tests of the infrared compound-eye imaging system show that the asymmetrical freeform lenslets are capable of steering and forming legible images within the design FOV. Compared to a conventional infrared camera, this novel microlens array can achieve a considerably larger FOV while maintaining low manufacturing cost without sacrificing image quality. Finally, two rapid heating processes are explored and demonstrated by using graphene-coated silicon as an effective and high-performance mold material for precision glass molding. One process is based on induction heating and the other one is based on mid-infrared radiation. Since the graphene coating is very thin (~45 nm), a high heating rate of 5~20 °C/s can be achieved. The contact surface of the Si mold and the polymer substrate can be heated above the Tg within 20 s and subsequently cooled down to room temperature within tens of seconds after molding. The feasibility of this process is validated by the fabrication of optical gratings, micropillar matrices, and microlens arrays on polymethylmethacrylate (PMMA) substrate with high precision. The uniformity and surface geometries of the replicated optical elements are evaluated using an optical profilometer. Compared with conventional bulk heating molding process, this novel rapid localized heating process could improve replication efficiency with better geometrical fidelity.

Author: Pedro B. Macedo
Publisher:
ISBN:
Category :
Languages : en
Pages : 10

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The research had as a primary goal the understanding of the basic chemical structure of glasses and their melts. Summarized is the research leading to the understanding of ionic migration in liquids and glasses, development of a chalcogenide glass ceramic for infrared windows, and use of laser light scattering to study composition fluctuations in liquids and glasses. (Author).

Author: Koto White
Publisher:
ISBN:
Category :
Languages : en
Pages : 78

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This report summarizes the literature search on glass-forming regions of chalcogenide compositional systems. Brief discussions on physical, chemical and structural properties are also included. This study was conducted to select and evaluate the chalcogenide glasses which are suitable for use in graded optical filter applications. Continuous variations of optical properties may be achieved by continuously varying the compositions of multicomponent glasses. The usefulness of this approach is severely limited in some multi-component glasses because of their tendency for phase separation and crystallization, which lead to inhomogeneous microstructures.

Author: Alvin W. Mao
Publisher:
ISBN: 9781339824819
Category :
Languages : en
Pages :

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Chalcogenide glasses exhibit unique optical properties such as infrared transparency owing to the low-phonon energies, optical non-linearity, and photo-induced effects that have important consequences for a wide range of technological applications. However, to fully utilize these properties, it is necessary to better understand the atomic-scale structure and structure-property relationships in this important class of materials. Of particular interest in this regard are glasses in the stoichiometric system Na2Se/BaSe--Ga2Se3--GeSe2 as they are isoelectronic with the well-studied, oxide glasses of the type M2O(M'O)--Al2O3SiO2 (M = alkali, M' = alkaline earth). This dissertation investigates the structure of stoichiometric Na2Se/BaSe--Ga2Se3--GeSe2 and off-stoichiometric BaSe--Ga2Se3--GeSe2±Se glasses using a combination of Fourier-transform Raman and solid state nuclear magnetic resonance (NMR) spectroscopies. The spectroscopic data is then compared to composition-dependent trends in physical properties such as density, optical band gap, glass transition temperature, and melt fragility to develop predictive structural models of the short- and intermediate-range order in the glass network. These models significantly improve our current understanding of the effects of modifier addition on the structure and properties of chalcogenide glasses, and thus enable a more efficient engineering of these highly functional materials for applications as solid electrolytes in batteries or as optical components in infrared photonics. In general, the underlying stoichiometric Ga2Se3--GeSe2 network consists primarily of corner-sharing (Ga/Ge)Se4 tetrahedra, where the coordination numbers of Ga, Ge, and Se are 4, 4, and 2, respectively. Some edge-sharing exists, but this configuration is relatively unstable and its concentration tends to decrease with any deviation from the GeSe2 composition. Due to the tetrahedral coordination of Ga, the initial addition of Se-deficient Ga2Se3 to GeSe2 results in the preferential formation of Ge-Ge bonds, which are distributed such that the clustering of ethane-like (Se3)Ge-Ge(Se3) units is avoided to the maximum extent. This behavior is entirely consistent with the continuously-alloyed structural scenario of chalcogenide glasses. However, for contents of Ga2Se3 greater than about 25--30 mol%, the avoidance of Ga-Ga and mixed Ga-Ge bonds results in the appearance of three-coordinated Se as an alternate mechanism to accommodate the Se deficiency. The addition of either Na2Se or BaSe to Ga2Se3--GeSe2 glasses introduces an ionic bonding character to an otherwise largely covalently bonded network. As a result, the structure responds by adopting characteristics of the charge-compensated structural scenario of oxide glasses. In the stoichiometric Na2Se/BaSe--Ga2Se3--GeSe2 glasses, the ratio of Na2Se/BaSe:Ga2Se3 = 1 serves as a chemical threshold, where the network consists predominantly of corner-sharing (Ga/Ge)Se4 tetrahedra, and the charge on the Na(Ba) cations is balanced by the GaSe4− tetrahedra. For glasses with Na2Se/BaSe:Ga2Se3 1, the addition of Se-deficient Ga2Se3 induces the formation of Ge-Ge bonds. However, for glasses with Na2Se/BaSe:Ga2Se3 1, the addition of Na2Se/BaSe results in the formation of non-bridging Se atoms, which break up the connectivity of the glassy network. The major difference between the modifying elements Na and Ba is that the high field strength of the Ba cation induces a higher degree of chemical disorder in the glass network. This conclusion is evidenced by the presence of some Ge-Ge bonds in BaSe--Ga2Se3--GeSe2 glasses even at the chemical threshold composition of BaSe:Ga2Se3 = 1. The structural duality of the Na2Se/BaSe--Ga2Se3--GeSe2 system is best observed in the off-stoichiometric BaSe--Ga2Se3--GeSe2±Se glasses. Here, the removal of Se from a stoichiometric glass with BaSe:Ga2Se3 > 1 results in Ge-Ge bonds, while its addition in excess of stoichiometry forms Se-Se bonds. Although such behavior is consistent with the continuously-alloyed structural model, it should be contrasted with the response of the network to the removal or addition of BaSe. In the latter case especially, the network responds with the formation of non-bridging Se atoms, which is reminiscent of the charge-compensated structural scenario. The aforementioned structural conclusions are supported by trends in physical properties. Of all the properties measured, the glass transition temperature Tg responds most predictably to changes in glass structure in the sense that the removal of heteropolar (Ga/Ge)-Se bonds from the glassy network consistently results in a decrease in Tg. Indeed, Tg is observed to be maximized around chemical threshold compositions that are expected to have a fully-connected network of (Ga/Ge)Se4 tetrahedra. The formation of homopolar Ge-Ge bonds causes Tg to drop by ~40-80 °C, while the formation of Se-Se and/or non-bridging Se causes Tg to decrease by at least 120 °C. Trends in density reflect both the packing efficiency of the structural units within the glassy network as well as the masses of the constituent elements, and are generally observed to increase or decrease monotonically. As a result, an increase in density is associated with: 1) the removal of inefficiently packed structural units such as edge-sharing tetrahedra, 2) the formation of efficiently packed units such as three-coordinated Se atoms, 3) the removal of lighter elements like Na, and 4) the addition of heavier elements like Ba. Optical band gap is related to the bonding character within the glassy network, and tends to decrease as the bonding character becomes increasingly metallic. Therefore, a decrease in optical band gap is observed with the formation of homopolar Ge-Ge bonds when Ga2Se3 is added to GeSe2. However, the stoichiometric BaSe--Ga2Se3--GeSe2 glasses show an anomaly in this regard because optical band gap decreases with the addition of BaSe, and consequently the removal of Ge-Ge bonds. This observation was ascribed instead to the formation of Ba-Se bonds, which are associated with a lower bandgap compared to the (Ga/Ge)-Se bonds that they replace. Finally, there is no straightforward structural explanation for trends in fragility, because it is related to the number of structural configurations dynamically available to the supercooled liquid. In the binary Ga2Se3--GeSe2 glasses, the fragility tends to increase with the formation of homopolar Ge-Ge bonds, which is consistent with other chalcogenide systems in which fragility increases with the removal of heteropolar bonds within corner-sharing tetrahedra and pyramids. In the stoichiometric BaSe--Ga2Se3--GeSe2 glasses on the other hand, a shift in trend near the compositions where BaSe:Ga2Se3 = 1 coincides with a structural shift between the formation of Ge-Ge bonds and Se-Se/non-bridging Se.

Author: Derrick Charles Kaseman
Publisher:
ISBN: 9781369343144
Category :
Languages : en
Pages :

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Chalcogenide glasses constitute an important class of materials that are sulfides, selenides or tellurides of group IV and/or V elements, namely Ge, As, P and Si with minor concentrations of other elements such as Ga, Sb, In. Because of their infrared transparency that can be tuned by changing chemistry and can be actively altered by exposure to band gap irradiation, chalcogenide glasses find use in passive and active optical devices for applications in the areas of photonics, remote sensing and memory technology. Therefore, it is important to establish predictive models of structure-property relationships for these materials for optimization of their physical properties for various applications. Structural elucidation of chalcogenide glasses is experimentally challenging and in order to make predictive structural models, structural units at both short and intermediate -range length scales must be identified and quantified. Nuclear Magnetic Resonance (NMR) spectroscopy is an element-specific structural probe that is uniquely suited for this task, but resolution and sensitivity issues have severely limited the applications of such techniques in the past. The recent development of multi-dimensional solid-state NMR techniques, such as Phase Adjusted Spinning Sidebands (PASS) and Magic Angle Turning (MAT) can potentially alleviate such issues. In this study novel two-dimensional, high-resolution 77Se and 125Te MATPASS NMR spectroscopic techniques are utilized to elucidate quantitatively the compositional evolution of the short- and intermediate- range atomic structure in three binary chalcogenide glass-forming systems, namely: Ge[subscript x]Se[subscript100-x], As[subscript x]Se[subscript 100-x], and As[subscript x]Te[subscript 100-x]. The spectroscopic results provide unambiguous site speciation and quantification for short- and intermediate-range structural motifs present in these glasses. In turn, for all systems, robust structural models and the corresponding structure-property relationships are successfully established as a function of composition. The results indicate that the physical properties are intimately tied to the topology and chemical order present in each system. Finally, a dynamic version of the two-dimensional 31P PASS NMR spectroscopy is used to study the molecular motion in a supercooled chalcogenide liquid of composition P5Se3. The results clearly display the presence of isotropic rotational reorientation of the constituent molecules at timescales significantly decoupled from that of the structural relaxation near and above T[subscript g]. This behavior is atypical of conventional molecular glasses in organic systems in which rotational and translational dynamics remain coupled near T[subscript g]. When taken together with previous reports on the dynamics of other globular inorganic molecules, the results support the existence of a “plastic glass” phase where the molecules perform rapid rotation without significant translation.

Author: Ting Wang
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Germanium-Arsenic-Selenium chalcogenide glasses are considered as good candidates for photonic applications due to their excellent transparency in the infrared range and high optical nonlinearities. A deep understanding of composition-structure-property relationship in Ge-As-Se ternary system is thus becoming increasingly important, which can serve as a guideline for materials selection. In this work, the structure and various physical properties of GexAsySe100-x-y bulk glasses have been systematically investigated. Raman spectra and EXAFS measurements reveal that chemically ordered network model can be applied to Selenium-rich glasses, but fails to explain bonding characterization of Selenium-poor compositions. Atomic arrangements are more sensitive to the changes in chemical compositions. A tight association between the fragility and the deviation from stoichiometry has been found in the Ge-As-Se system by differential scanning calorimetry. It is shown that chemical compositions with the lowest values of fragility index are far less likely to incur structural relaxation. Those strong glasses are normally chosen as ideal materials for fabrication of stable photonic devices. The variation of density and elastic modulus as a function of mean coordination number both show two transition thresholds, which correlate with floppy-to-rigid phase transition and 2D-to-3D structure transition respectively. The results provide clear evidence that some physical properties of Ge-As-Se chalcogenide glasses are significantly determined by their mean coordination numbers, but could be further tuned by the chemical compositions. The detailed optical investigation shows that the generalized Miller's rule is a simple but effective approach to estimate the nonlinearities of a broad variety of chalcogenide glasses. Nonlinear properties of these materials exhibit strong dependence upon their optical bandgap in the near infrared. It seems that the highest nonlinearity at telecommunications wavelengths is predictable in chalcogenide glasses.

Author:
Publisher:
ISBN:
Category : Artificial intelligence
Languages : en
Pages : 336

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