DOCSLIB.ORG

Production(?) of Chalcogenide Glass Optics : Xiang-Hua ZHANG, Laurent

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Production(?) of Chalcogenide Glass Optics : Xiang-Hua ZHANG, Laurent Production(?) of chalcogenide glass optics : motivation, current status and future development Xiang-Hua ZHANG, Laurent CALVEZ Hongli MA and Jacques LUCAS Laboratory of glasses and ceramics, UMR CNRS “Sciences chimiques de Rennes”, Université de Rennes I, 35042 Rennes cedex, France Outline Background and motivations Current technique for chalcogenide glass fabrication Challenges and future trends for chalcogenide glass and lens fabrication Summary Thermal imaging was developed for defense application with more and more commercial applications Why infrared is interesting for driving assistance Visible camera Infrared camera Thermal Imaging – A growing market 350 Driver's vision enhancement 300 Maintenance 250 Process control Fire fighting 200 Surveillance 150 Other commercial applications Weapon guidance MillionsMillions US US dollars dollars 100 Civil and military ground applications 50 Other civil and military applications 0 2005 2006 2007 2008 2009 2010 2011 Year Great progress achieved in uncooled infrared detectors Constant need for cheaper, more efficient materials Thermal Imaging : how it works Based on the detection of the radiations emitted by hot bodies Visible range 3-5µm 8-12µm Atmospheric transmission ) -1 14 .m 10 -1 13 .sr 10 -2 6000K 10 12 11 (W.m 10 3000K 10 10 9 10 1000K 10 8 500K 10 7 10 6 300K 5 200K 10 10 4 100K 10 3 10 2 10 1 10 0 Monochromatic luminescence energyenergy luminescence luminescence Monochromatic Monochromatic 0,1 1 10 100 Wavelength (µm) • 2nd atmospheric window (MWIR) : 3-5 µm • 3rd atmospheric window (LWIR) : 8-12 µm Need for materials transparent in these windows Cost of Infrared detectors euros) Defense consumer Cost of detector + cooler ( ( coolercooler++ detectordetector of of CostCost Typical IR Optics Materials for thermal imaging optics Single Crystalline Germanium • Expensive • Single point diamond turning Polycrystalline Zinc Selenide (ZnSe) • Synthesized by CVD • Single point diamond turning Chalcogenide glasses - Definition S Se Te Ga Ge As Sb Chalcogenide glasses - Properties Silica Fluorides Sulfides Large Selenides transparency Tellurides in the Infrared Wavelength (µm) moldable Low dn/dT Bulk / Fibers Lenses Chalcogenide glass samples Chalcogenide glass synthesis Vacuum pump Sealing Liquid Nitrogen Starting raw elements quenching Industrial fabrication of chalcogenide glass Ge-As-Se Dr. A. Ray Hilton, Sr. Amorphous Materials, Inc. Garland, Texas Industrial fabrication of chalcogenide glass Ge-As-Se Dr. A. Ray Hilton, Sr. Amorphous Materials, Inc. Garland, Texas Casting of chalcogenide glass Dr. A. Ray Hilton, Sr. Amorphous Materials, Inc. Casting of chalcogenide glass Different steps of Chalcogenide glass production Maximum size : 200 mm Raw materials, sealed under vacuum Reaction et distillation Homogenisation, cooling and annealing Homogeneity control CCD Camera Glass to be controlled Homogeneity control Fabrication of optical lenses Grinding/polishing : spherical surfaces Single point diamond turning Molding Molding of chalcogenid glass lenses Examples of molded chalcogenide glass optics Challenges for chalcogenide glass molding Sumitomo patent In inert gas or in vacuum to avoid upper mold oxidation vapor pressure non negligible at Ts glass Necessity to prepare preform before molding lower mold Toshiba patented molding machine Amorphous Materials Inc molding machine Challenges and future trends for chalcogenide glass and lens fabrication Synthesis of chalcogenide glasses 100000 S As Se 10000 Important difference in Te Sb vapor pressures for the 1000 Ga different elements 100 Ge 10 Vapor Pressure Vapor (Pa) Pressure Closed systems 1 200 400 600 800 1000 1200 1400 1600 1800 2000 Temperature (°C) Highly sensitive to contamination by oxygen Controlled atmosphere Set-up for chalcogenide glass synthesis in argon Vapor pressure of As and Se Vapor pressure (Pa) (Pa) pressure pressure Vapor Vapor Temperature ( °C) Photos of good sample Example of glass obtained with sealed λ=3-5 µm silica tube Index reproducibility 3 glasses tested Index precision :2.10 -3 Index at 1.55 µm glasses Lower Upper difference Techniquesample cansample not be used for synthesizingA 2.8204 Germanium 2.8198 containing6. 10 -4 glass B 2.8112 2.8120 - 8. 10 -4 C 2.8099 2.8104 - 5. 10 -4 Difference B-C 3. 10 -4 1.6. 10 -3 Continuous production line Umicore patent For IR optics New approach for chalcogenide glass production Mechanosynthesis using mechanical energy instead of thermal energy to induce chemical reaction Starting elements Mechanosynthesis Glass powder Milling jar Consolidation Milling balls • Melting in reusable silica chamber • Hot Uniaxial Pressing Bulk material • Spark Plasma Sintering Mechanosynthesis 80GeSe 2-20Ga 2Se 3 Evolution of powder coloration with milling duration 0h3h 5h 8h 10h 20h 40h 80h Progressive reaction between the elements and lowering of particle size Particle size distribution XRD Spectra 6 3000 10h 80h 5 3h 2500 40h 4 2000 20h 40h 10h 3 1500 8h 80h 2 1000 5h Frequency (%/µm) 1 units) counts(arb. 500 3h 0 Ge 0,1 1 10 100 1000 10 20 30 40 50 60 70 Particle size (µm) Angle (°2 θθθ) Mechanosynthesis • Synthesis of micrometric glass powder • Thermal properties close to that of glasses prepared in sealed silica ampoule To produce bulk glasses or optics Melting and casting Sintering Melting of the powders/casting experimental set-up Agitation system In closed silica chamber under Argon Argon argon atmosphere exit entrance The powders already possess the desired composition Rotating Helix Reduced risks of Furnace evaporation of selenium Glass Bulk glass/lenses fabrication by hot pressing Principle: sintering of the powder at a temperature above the glass transition temperature (Tg) but below the melting temperature (Tm) Hot Uniaxial Pressing (HUP) Spark Plasma Sintering (SPS) Pressure control Pressure control P P furnace Vacuum die chamber powder Power pistons powder supply protective plate P P Faster temperature ramps reached with SPS Conventional hot pressing needs stable glasses 80GeSe 2-20Ga 2Se 3 composition: ∆T<100 °C Materials obtained: • Inhomogeneous sintering (thermal profile of the press) • Uncontrolled crystallization • No optical transmission 1µm Crystallization due to prolonged stages at T>Tg Need to reduce sintering process duration => SPS Fast sintering of 80GeSe 2-20Ga 2Se 3 powder with SPS Experimental conditions Dr Synter 505 Syntex SPS machine • Under vacuum • Thermal treatment 2 min, 390°C 400 350 300 Densification > 99% 250 200 150 Temperature (°C) (°C) Temperature Temperature 100 50 0 0 2 4 6 8 10 Time (min) Sample surface area x 16 Total duration: 10 min (more than 2h for HUP) glass bulks sintered at different dwell temperatures (50 MPa, 2-min ) 250 °C 350 °C 390 °C G. Delaizir et al J. Am. Ceram. Soc., 95 [7] 2211–2217 (2012) Fast sintered 80GeSe 2-20Ga 2Se 3 glass discs Powder sintered 2 minutes at 390 °C (Tg+40 °C), 50MPa Thermal camera visible 8-12µm Densification > 99% Transparent bulk samples Ø = 8 mm, 20 mm et 36 mm Maximum diameter obtained using silica tubes = 9 mm Fast sintered 80GeSe 2-20Ga 2Se 3 Glass-Ceramics Sintering at 390 °C for longer durations 2 min 15 min 30 min 60 min 70 • Progressive controllable Glass prepared 0.3 60 in silica tube crystallization (crystals < 100 nm) 2 min and ground 50 0.2 15 min • Glass-ceramics transparent in the 40 0.1 infrared range 30 30 min Ge-O critical load (N). Transmission Transmission (%) 20 0• Important pollution by oxygen 0 20 40 60 80 100 120 140 10 60 min (transmission cut-off at 12 µm) Ceramisation time (hours) 0 0 2 4 6 8 10 12 14 16 18 20 Cooperation with LARMAUR Wavelength (µm) Summary Chalcogenide glasses are fabricated batch by batch in sealed silica tube Discontinued process Expensive single use silica ampoules Only for highly stable glasses Fabrication in controlled atmosphere Highly homogenous glasses Only for Ge-free glasses Mechano-synthesis + Spark plasma Sintering Possibility of continuous process Wide choice of glass composition Large size glass ceramic optics We need process revolution.
Load more

Recommended publications
  • Glossary Physics (I-Introduction)
    1 Glossary Physics (I-introduction) - Efficiency: The percent of the work put into a machine that is converted into useful work output; = work done / energy used [-]. = eta In machines: The work output of any machine cannot exceed the work input (<=100%); in an ideal machine, where no energy is transformed into heat: work(input) = work(output), =100%. Energy: The property of a system that enables it to do work. Conservation o. E.: Energy cannot be created or destroyed; it may be transformed from one form into another, but the total amount of energy never changes. Equilibrium: The state of an object when not acted upon by a net force or net torque; an object in equilibrium may be at rest or moving at uniform velocity - not accelerating. Mechanical E.: The state of an object or system of objects for which any impressed forces cancels to zero and no acceleration occurs. Dynamic E.: Object is moving without experiencing acceleration. Static E.: Object is at rest.F Force: The influence that can cause an object to be accelerated or retarded; is always in the direction of the net force, hence a vector quantity; the four elementary forces are: Electromagnetic F.: Is an attraction or repulsion G, gravit. const.6.672E-11[Nm2/kg2] between electric charges: d, distance [m] 2 2 2 2 F = 1/(40) (q1q2/d ) [(CC/m )(Nm /C )] = [N] m,M, mass [kg] Gravitational F.: Is a mutual attraction between all masses: q, charge [As] [C] 2 2 2 2 F = GmM/d [Nm /kg kg 1/m ] = [N] 0, dielectric constant Strong F.: (nuclear force) Acts within the nuclei of atoms: 8.854E-12 [C2/Nm2] [F/m] 2 2 2 2 2 F = 1/(40) (e /d ) [(CC/m )(Nm /C )] = [N] , 3.14 [-] Weak F.: Manifests itself in special reactions among elementary e, 1.60210 E-19 [As] [C] particles, such as the reaction that occur in radioactive decay.
    [Show full text]
  • Molecular Materials for Nonlinear Optics
    RICHARD S. POTEMBER, ROBERT C. HOFFMAN, KAREN A. STETYICK, ROBERT A. MURPHY, and KENNETH R. SPECK MOLECULAR MATERIALS FOR NONLINEAR OPTICS An overview of our recent advances in the investigation of molecular materials for nonlinear optical applications is presented. Applications of these materials include optically bistable devices, optical limiters, and harmonic generators. INTRODUCTION of potentially important optical qualities and capabilities Organic molecular materials are a class of materials such as optical bistability, optical threshold switching, in which the organic molecules retain their geometry and photoconductivity, harmonic generation, optical para­ physical properties when crystallization takes place. metric oscillation, and electro-optic modulation. A sam­ Changes occur in the physical properties of individual ple of various applications for several optical materials molecules during crystallization, but they are small com­ is shown in Table 1. pared with those that occur in ionic or metallic solids. The optical effects so far observed in many organic The energies binding the individual molecules together materials result from the interaction of light with bulk in organic solids are also relatively small, making organic materials such as solutions, single crystals, polycrystal­ molecular solids mere aggregations of molecules held to­ line fIlms, and amorphous compositions. In these materi­ gether by weak intermolecular (van der Waals) forces . als, each molecule in the solid responds identically, so The crystalline structure of most organic molecular solids that the response of the bulk material is the sum of the is more complex than that of most metals or inorganic responses of the individual molecules. That effect sug­ solids; 1 the asymmetry of most organic molecules makes gests that it may be possible to store and process optical the intermolecular forces highly anisotropic.
    [Show full text]
  • The American Ceramic Society 25Th International Congress On
    The American Ceramic Society 25th International Congress on Glass (ICG 2019) ABSTRACT BOOK June 9–14, 2019 Boston, Massachusetts USA Introduction This volume contains abstracts for over 900 presentations during the 2019 Conference on International Commission on Glass Meeting (ICG 2019) in Boston, Massachusetts. The abstracts are reproduced as submitted by authors, a format that provides for longer, more detailed descriptions of papers. The American Ceramic Society accepts no responsibility for the content or quality of the abstract content. Abstracts are arranged by day, then by symposium and session title. An Author Index appears at the back of this book. The Meeting Guide contains locations of sessions with times, titles and authors of papers, but not presentation abstracts. How to Use the Abstract Book Refer to the Table of Contents to determine page numbers on which specific session abstracts begin. At the beginning of each session are headings that list session title, location and session chair. Starting times for presentations and paper numbers precede each paper title. The Author Index lists each author and the page number on which their abstract can be found. Copyright © 2019 The American Ceramic Society (www.ceramics.org). All rights reserved. MEETING REGULATIONS The American Ceramic Society is a nonprofit scientific organization that facilitates whether in print, electronic or other media, including The American Ceramic Society’s the exchange of knowledge meetings and publication of papers for future reference. website. By participating in the conference, you grant The American Ceramic Society The Society owns and retains full right to control its publications and its meetings.
    [Show full text]
  • 25 Geometric Optics
    CHAPTER 25 | GEOMETRIC OPTICS 887 25 GEOMETRIC OPTICS Figure 25.1 Image seen as a result of reflection of light on a plane smooth surface. (credit: NASA Goddard Photo and Video, via Flickr) Learning Objectives 25.1. The Ray Aspect of Light • List the ways by which light travels from a source to another location. 25.2. The Law of Reflection • Explain reflection of light from polished and rough surfaces. 25.3. The Law of Refraction • Determine the index of refraction, given the speed of light in a medium. 25.4. Total Internal Reflection • Explain the phenomenon of total internal reflection. • Describe the workings and uses of fiber optics. • Analyze the reason for the sparkle of diamonds. 25.5. Dispersion: The Rainbow and Prisms • Explain the phenomenon of dispersion and discuss its advantages and disadvantages. 25.6. Image Formation by Lenses • List the rules for ray tracking for thin lenses. • Illustrate the formation of images using the technique of ray tracking. • Determine power of a lens given the focal length. 25.7. Image Formation by Mirrors • Illustrate image formation in a flat mirror. • Explain with ray diagrams the formation of an image using spherical mirrors. • Determine focal length and magnification given radius of curvature, distance of object and image. Introduction to Geometric Optics Geometric Optics Light from this page or screen is formed into an image by the lens of your eye, much as the lens of the camera that made this photograph. Mirrors, like lenses, can also form images that in turn are captured by your eye. 888 CHAPTER 25 | GEOMETRIC OPTICS Our lives are filled with light.
    [Show full text]
  • Antireflective Coatings
    materials Review Antireflective Coatings: Conventional Stacking Layers and Ultrathin Plasmonic Metasurfaces, A Mini-Review Mehdi Keshavarz Hedayati 1,* and Mady Elbahri 1,2,3,* 1 Nanochemistry and Nanoengineering, Institute for Materials Science, Faculty of Engineering, Christian-Albrechts-Universität zu Kiel, Kiel 24143, Germany 2 Nanochemistry and Nanoengineering, Helmholtz-Zentrum Geesthacht, Geesthacht 21502, Germany 3 Nanochemistry and Nanoengineering, School of Chemical Technology, Aalto University, Kemistintie 1, Aalto 00076, Finland * Correspondence: [email protected] (M.K.H.); mady.elbahri@aalto.fi (M.E.); Tel.: +49-431-880-6148 (M.K.H.); +49-431-880-6230 (M.E.) Academic Editor: Lioz Etgar Received: 2 May 2016; Accepted: 15 June 2016; Published: 21 June 2016 Abstract: Reduction of unwanted light reflection from a surface of a substance is very essential for improvement of the performance of optical and photonic devices. Antireflective coatings (ARCs) made of single or stacking layers of dielectrics, nano/microstructures or a mixture of both are the conventional design geometry for suppression of reflection. Recent progress in theoretical nanophotonics and nanofabrication has enabled more flexibility in design and fabrication of miniaturized coatings which has in turn advanced the field of ARCs considerably. In particular, the emergence of plasmonic and metasurfaces allows for the realization of broadband and angular-insensitive ARC coatings at an order of magnitude thinner than the operational wavelengths. In this review, a short overview of the development of ARCs, with particular attention paid to the state-of-the-art plasmonic- and metasurface-based antireflective surfaces, is presented. Keywords: antireflective coating; plasmonic metasurface; absorbing antireflective coating; antireflection 1.
    [Show full text]
  • Fiber Optics Standard Dictionary
    FIBER OPTICS STANDARD DICTIONARY THIRD EDITION JOIN US ON THE INTERNET WWW: http://www.thomson.com EMAIL: [email protected] thomson.com is the on-line portal for the products, services and resources available from International Thomson Publishing (ITP). This Internet kiosk gives users immediate access to more than 34 ITP publishers and over 20,000 products. Through thomson.com Internet users can search catalogs, examine subject-specific resource centers and subscribe to electronic discussion lists. You can purchase ITP products from your local bookseller, or directly through thomson.com. Visit Chapman & Hall's Internet Resource Center for information on our new publications, links to useful sites on the World Wide Web and an opportunity to join our e-mail mailing list. Point your browser to: bttp:/Iwww.cbapball.com or http://www.thomson.com/chaphaWelecteng.html for Electrical Engineering A service of I ® JI FIBER OPTICS STANDARD DICTIONARY THIRD EDITION MARTIN H. WEIK SPRINGER-SCIENCE+BUSINESS MEDIA, B.v. JOIN US ON THE INTERNET WWW: http://www.thomson.com EMAIL: [email protected] thomson.com is the on-line portal for the products, services and resources available from International Thomson Publishing (ITP). This Internet kiosk gives users immediate access to more than 34 ITP publishers and over 20,000 products. Through thomson.com Internet users can search catalogs, examine subject­ specific resource centers and subscribe to electronic discussion lists. You can purchase ITP products from your local bookseller, or directly through thomson.com. Cover Design: Said Sayrafiezadeh, Emdash Inc. Copyright © 1997 Springer Science+Business Media Dordrecht Originally published by Chapman & Hali in 1997 Softcover reprint ofthe hardcover 3rd edition 1997 Ali rights reserved.
    [Show full text]
  • Fiber Optic Communications
    FIBER OPTIC COMMUNICATIONS EE4367 Telecom. Switching & Transmission Prof. Murat Torlak Optical Fibers Fiber optics (optical fibers) are long, thin strands of very pure glass about the size of a human hair. They are arranged in bundles called optical cables and used to transmit signals over long distances. EE4367 Telecom. Switching & Transmission Prof. Murat Torlak Fiber Optic Data Transmission Systems Fiber optic data transmission systems send information over fiber by turning electronic signals into light. Light refers to more than the portion of the electromagnetic spectrum that is near to what is visible to the human eye. The electromagnetic spectrum is composed of visible and near -infrared light like that transmitted by fiber, and all other wavelengths used to transmit signals such as AM and FM radio and television. The electromagnetic spectrum. Only a very small part of it is perceived by the human eye as light. EE4367 Telecom. Switching & Transmission Prof. Murat Torlak Fiber Optics Transmission Low Attenuation Very High Bandwidth (THz) Small Size and Low Weight No Electromagnetic Interference Low Security Risk Elements of Optical Transmission Electrical-to-optical Transducers Optical Media Optical-to-electrical Transducers Digital Signal Processing, repeaters and clock recovery. EE4367 Telecom. Switching & Transmission Prof. Murat Torlak Types of Optical Fiber Multi Mode : (a) Step-index – Core and Cladding material has uniform but different refractive index. (b) Graded Index – Core material has variable index as a function of the radial distance from the center. Single Mode – The core diameter is almost equal to the wave length of the emitted light so that it propagates along a single path.
    [Show full text]
  • Technical Glasses
    Technical Glasses Physical and Technical Properties 2 SCHOTT is an international technology group with 130 years of ex­ perience in the areas of specialty glasses and materials and advanced technologies. With our high­quality products and intelligent solutions, we contribute to our customers’ success and make SCHOTT part of everyone’s life. For 130 years, SCHOTT has been shaping the future of glass technol­ ogy. The Otto Schott Research Center in Mainz is one of the world’s leading glass research institutions. With our development center in Duryea, Pennsylvania (USA), and technical support centers in Asia, North America and Europe, we are present in close proximity to our customers around the globe. 3 Foreword Apart from its application in optics, glass as a technical ma­ SCHOTT Technical Glasses offers pertinent information in terial has exerted a formative influence on the development concise form. It contains general information for the deter­ of important technological fields such as chemistry, pharma­ mination and evaluation of important glass properties and ceutics, automotive, optics, optoelectronics and information also informs about specific chemical and physical character­ technology. Traditional areas of technical application for istics and possible applications of the commercial technical glass, such as laboratory apparatuses, flat panel displays and glasses produced by SCHOTT. With this brochure, we hope light sources with their various requirements on chemical­ to assist scientists, engineers, and designers in making the physical properties, have led to the development of a great appropriate choice and make optimum use of SCHOTT variety of special glass types. Through new fields of appli­ products. cation, particularly in optoelectronics, this variety of glass types and their modes of application have been continually Users should keep in mind that the curves or sets of curves enhanced, and new forming processes have been devel­ shown in the diagrams are not based on precision measure­ oped.
    [Show full text]
  • COATING TRACES Coating
    Backgrounder COATING TRACES Coating HIGH REFLECTION COATING TRACES ND:YAG/ND:YLF ..........................................................................................................T-26 TUNABLE LASER MIRRORS .........................................................................................T-28 Coating Traces MISCELLANEOUS MIRRORS ........................................................................................T-30 ANTI-REFLECTION COATING TRACES ANTI-REFLECTIVE OVERVIEW ....................................................................................T-31 0 DEGREE ANGLE OF INCIDENCE ............................................................................T-33 Material Properties 45 DEGREE ANGLE OF INCIDENCE ..........................................................................T-36 CUBES AND POLARIZING COMPONENTS TRACES .........................................................T-38 Optical Specifications cvilaseroptics.com T-25 HIGH REFLECTION COATING TRACES: Y1-Y4, HM AT 0 DEGREE INCIDENCE Optical Coatings and Materials Traces Y1 - 1064nm - 0 DEGREES Y2 - 532nm - 0 DEGREES Y3 - 355nm - 0 DEGREES Y4 - 266nm - 0 DEGREES HM - 1064/532nm - 0 DEGREES P-POL: UNP: - - - - - S-POL: 0°: - - - - - - T-26 cvilaseroptics.com Backgrounder Coating HIGH REFLECTION COATING TRACES: Y1-Y4, HM, YH, AT 45 DEGREE INCIDENCE Y1 - 1064nm - 45 DEGREES Y2 - 532nm - 45 DEGREES Coating Traces Material Properties Y3 - 355nm - 45 DEGREES Y4 - 266nm - 45 DEGREES Optical Specifications HM - 1064/532nm - 45 DEGREES YH - 1064/633nm - 45 DEGREES
    [Show full text]
  • Antireflection Coatings for High Power Fiber Laser Optics Authors: Gherorghe Honciuc, Emiliano Ioffe, Jurgen Kolbe, Ophir Optics Group, MKS Instruments Inc
    Antireflection Coatings for High Power Fiber Laser Optics Authors: Gherorghe Honciuc, Emiliano Ioffe, Jurgen Kolbe, Ophir Optics Group, MKS Instruments Inc. INTRODUCTION Finally, a long service life of the optics is important for the High-power kilowatt-level fiber lasers (wavelength in spec- user in order to minimize downtime of the laser machine. tral range 1.0 – 1.1µm) are used in important applications This can be achieved only if absorption of the AR coatings in macro material processing, particularly for cutting and is very low. welding metal sheets. In these applications, optics (lenses, In this paper, we review the materials, coating technolo- protective windows) are needed to work properly at corre- gies and measurement techniques used at Ophir Optics spondingly high laser power and power density levels. For for high-performance low absorption fiber laser optics these optics, absorption losses are of crucial importance: manufacturing. absorption of laser radiation leads to increased tempera- ture and a correspondingly higher refractive index of the RAW MATERIAL optics. This changes the properties of the transmitted la- There are two material categories regarding the ser beam and can therefore impair the performance of the absorption of fused silica: manufacturing process. In addition, temperature increase • (a) Fused silica with absorption greater than 1 ppm/cm, can cause internal mechanical stress and eventually dam- e. g. Corning 7980 age the optics. To avoid this, optics with lowest possible • (b) Fused silica with absorption less than 1 ppm/cm, [1] absorption losses must be used. e. g. Suprasil 3001 . The most common raw material for these optics is fused Due to the high cost of material of category (b), it should silica which is available with sufficiently low absorption.
    [Show full text]
  • Crystallization Kinetics of Chalcogenide Glasses
    2 Crystallization Kinetics of Chalcogenide Glasses Abhay Kumar Singh Department of Physics, Banaras Hindu University, Varanasi, India 1. Introduction 1.1 Background of chalcogenides Chalcogenide glasses are disordered non crystalline materials which have pronounced tendency their atoms to link together to form link chain. Chalcogenide glasses can be obtained by mixing the chalcogen elements, viz, S, Se and Te with elements of the periodic table such as Ga, In, Si, Ge, Sn, As, Sb and Bi, Ag, Cd, Zn etc. In these glasses, short-range inter-atomic forces are predominantly covalent: strong in magnitude and highly directional, whereas weak van der Waals' forces contribute significantly to the medium-range order. The atomic bonding structure is, in general more rigid than that of organic polymers and more flexible than that of oxide glasses. Accordingly, the glass-transition temperatures and elastic properties lay in between those of these materials. Some metallic element containing chalcogenide glasses behave as (super) ionic conductors. These glasses also behave as semiconductors or, more strictly, they are a kind of amorphous semi-conductors with band gap energies of 1±3eV (Fritzsche, 1971). Commonly, chalcogenide glasses have much lower mechanical strength and thermal stability as compared to existing oxide glasses, but they have higher thermal expansion, refractive index, larger range of infrared transparency and higher order of optical non-linearity. It is difficult to define with accuracy when mankind first fabricated its own glass but sources demonstrate that it discovered 10,000 years back in time. It is also difficult to point in time, when the field of chalcogenide glasses started.
    [Show full text]
  • Chapter 19/ Optical Properties
    Chapter 19 /Optical Properties The four notched and transpar- ent rods shown in this photograph demonstrate the phenomenon of photoelasticity. When elastically deformed, the optical properties (e.g., index of refraction) of a photoelastic specimen become anisotropic. Using a special optical system and polarized light, the stress distribution within the speci- men may be deduced from inter- ference fringes that are produced. These fringes within the four photoelastic specimens shown in the photograph indicate how the stress concentration and distribu- tion change with notch geometry for an axial tensile stress. (Photo- graph courtesy of Measurements Group, Inc., Raleigh, North Carolina.) Why Study the Optical Properties of Materials? When materials are exposed to electromagnetic radia- materials, we note that the performance of optical tion, it is sometimes important to be able to predict fibers is increased by introducing a gradual variation and alter their responses. This is possible when we are of the index of refraction (i.e., a graded index) at the familiar with their optical properties, and understand outer surface of the fiber. This is accomplished by the mechanisms responsible for their optical behaviors. the addition of specific impurities in controlled For example, in Section 19.14 on optical fiber concentrations. 766 Learning Objectives After careful study of this chapter you should be able to do the following: 1. Compute the energy of a photon given its fre- 5. Describe the mechanism of photon absorption quency and the value of Planck’s constant. for (a) high-purity insulators and semiconduc- 2. Briefly describe electronic polarization that re- tors, and (b) insulators and semiconductors that sults from electromagnetic radiation-atomic in- contain electrically active defects.
    [Show full text]