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Chapter 19 Optical Properties Group Four Part One : Colorful scenes from the opening ceremony of Beijing Olympic Games. Concepts Basic concepts Properties Applications Part Two : Question: What is the earliest mirror made of? Part Two : Question: Why could bronze reflect light? Concepts Basic concepts Properties Optical properties of metals Applications Part Three : Experiment Manmade Rainbow Concepts Basic concepts Properties Optical properties of metals Optical properties of nonmetals Applications Part Four : News: Head knocked on glass door. Who is to be blamed? ※ Mr Yang himself? ※ The hotel? ※ The glass door? Question:: Why glasses are transparent? Concepts Basic concepts Properties Optical properties of metals Optical properties of nonmetals Applications Part Five : Let’s take a break and see a video. Question: What is she holding? Concepts Basic concepts Properties Applications Optical properties of metals Laser Optical properties of nonmetals Part Six : Example: Widespread use of optical fiber. Concepts Basic concepts Properties Applications Optical properties of metals Laser Optical properties of nonmetals Optical fiber Summary: Concepts Basic concepts Properties Applications Optical properties of metals luminescence photoconducti vity Laser Optical properties of nonmetals Optical fiber Repoter: Luo tian huan Why could she see herself in the Bronze Mirror ? Optical Properties of Metals Procedure Basic nature The electron energy band schemes for metals Properties Light absorption and reflection for metals Performance For visible light, Metals are opaque → Perceived colors Application Stimulation for metals to launch X-rays as the invisible radiation Network Optimization Expert Team The electron energy band schemes for metals • • solids at 0 K. (a)The electron band structure found in metals such as copper, in which there are available electron states above and adjacent to filled states, in the same band. (b) The electron band structure of metals such as magnesium(Mg), wherein there is an overlap of filled and empty outer bands. Light Absorption for Metals 2011-12-2 Light Reflection for Metals 2011-12-2 Metals are opaque The reflectivity :0.90 ~0.95; Small fraction dissipated as heat. Total absorption is within a very thin outer layer, less than 0.1 μm Perceived Colors Determined by the wavelength distribution of the radiation that is reflected and not absorbed. 2011-12-2 Copper Aluminum 2011-12-2 Gold Silver The X-ray Rainbows 2011-12-2 The stimulation of X-ray Professor Li • When the moving electrons flow in high velocity striking the anode materials such as Chromium(Cr);Iron(Fe);Cobalt(Co);Nickel(Ni);Copper(Cu) and so forth, X-rays will be radiated which is in high frequencies. 2011-12-2 Medical Examination 2011-12-2 Metal Defect Detection 2011-12-2 Scientific or technical literature Science 12 February 1971: Vol. 171 no. 3971 pp. 567-571 DOI: 10.1126/science.171.3971.567 Named:Alteration of Lunar Optical Properties: Age and Composition Effects Science journal Named:Muscles Made from Metal Ray H. Baughman Science 11 April 2003: 268-269. [DOI:10.1126/science.1082270] IEEE JOURNALS Named:The optical properties of metals Ehrenreich, Henry; Harvard University Volume: 2 , Issue: 3 Digital Object Identifier: 10.1109/MSPEC.1965.5531773 Publication Year: 1965 , Page(s): 162 - 170 2011-12-2 Thank you ! Optical properties ------- non-metals Reporter mkk 1 Optical properties of non-metals incident light non-metals transmitted light reflected light absorbed light Classification: I = T + R + A 2 Part one Transmitted light: Refraction Definition : Light that is transmitted into the interior of transparent materials experiences a decrease in velocity, and, as a result, is bent at the interface; this phenomenon is termed refraction. Index of refraction phenomena: n= c / v The experiment We have seen 3 Principle : electronic polarization Part one Result 1 : --Light is slower in a material --Light can be "bent" Result 2 : Intensity of transmitted light decreases with distance traveled (thick pieces less transparent!) 4 Reflection Part two Definition : When light radiation passes from one medium into another having a different index of refraction, some of the light is scattered at the interface between the two media even if both are transparent. Principle: electron transitions The principle is similar to the reflection in the metals. 5 Part two Do you know why optical instruments are always coated with very thin layers of materials such as magnesium fluoride (MgF2 ) at the reflecting surface ? 6 Part two The reflectivity R (反射率) index of refraction of air is 1 The higher the index of refraction of the solid, the greater is the reflectivity. 7 Part three Nonmetals :Selected absorption Condition : Absorption by electron transition occurs if Hν > Egap 8 Part three A photon energy (in visible light) 1.8eV red) ( < hν < ( 3.1eV purple) • If Egap < 1.8eV, full absorption; color is black (Si, GaAs) • If Egap > 3.1eV, no absorption; colorless (diamond) • If Egap in between, partial absorption; material has a color. Xu xiao mei 9 Thank you ! 10 Optical Fiber Communication 光纤通信 Jason (钱晨) Prof. Charles Kao Father of Optical Fiber Communication Win The Nobel Prize in Physics 2009 “For groundbreaking achievements concerning the transmission of light in fibers for optical communication.” Optical Fiber Technology A Revolution Optical Fiber Technology Optical Fibers V.S. Copper Wires Speed of Transmission Information Density Transmission Distance Error Rate Electromagnetic Interference Optical Fiber Communication System Optical Fiber——Heart of The System Guide Light Pulses Avoid Power Loss Avoid Pulse Distortion Fiber Components Core Let the signal pass through. Cladding Let the light rays travel within the core. Coating Protect core and cladding from damage. Two Optical Fiber Designs Step-index Optical Fiber Design Graded-index Optical Fiber Design Summary Optical Fiber Technology ——Improve speed of transmission, information density, transmission distance. Optical Fiber ——Heart of The Communication System. Fiber Components ——Core, Cladding, Coating. Two Optical Fiber Designs ——Step-index, Graded-index. One Application of optical phenomena——The magic laser Jin Wong What’s your feeling after watching the video? • Excited? • Amazed? • Surprised? What laser is? How can we get the laser? • ——Let’s search the answer. LASER Light Amplification by Stimulated Emission of Radiation Stimulated Emission Light Amplification (受激发射) (光放大) The process of Stimulated Emission E1 E3 (10-8sec) pro Key ce ss E2 (10-3 sec) (accumulation) Light Amplification The properties of laser monochromatic directional coherent (单色的) (定向的) (相干的) Star Wars in the real world! Laser Weapons Powerful! Laser Processing How can laser benefit our major? Laser heat treatment (激 Laser welding 光热处理) diamond(激光焊 接金刚石) Thank you for listening! Our performance is going on~~ Optical properties Color Translucency Opacity By Xuxiaomei RAPIDESIGN 1.The mechanism of color The mechanism of color Materials appear colored as a consequence of specific wavelength ranges of light that are selectively absorbed(选择性吸收). 3.1eV 1.8eV 2.4eV absorbed Transmitted (透射) Reemitted (重发射) The fraction of the visible light having energies greater than Eg is selectively absorbed by valence band–conduction band electron transitions(跃迁). absorbed CdS,Eg=2.4eV transmitted reemitted Sapphire (单晶氧化铝) Ruby (sapphire added 0.5 ~2% of chromium oxide) 2.Specific impurities can change the color 3.Application of color Glaze(上釉) is a thin shiny coating, or the act of applying the coating; it is used for decorating or protecting materials. WINTER Optic materials Template Transparency (透明) Translucency (半透明) single‐crystal fully dense polycrystal Opacity (不透明) polycrystal contain porosity (气孔) 02 Pore(气孔) Grain boundary Grain boundary A transmitted light beam is deflected(偏离) in direction and lead to scattering(散射). Hope you enjoy it! THANK YOU RAPIDESIGN Chapter 19 Optical Properties BASIC CONCEPTS ——Xu Hong Contents Electromagnetic Radiation Light Interaction With Solids Electronic Polarization Electron Transitions Contents Electromagnetic Radiation Light Interaction With Solids Electronic Polarization Electron Transitions Electromagnetic Radiation Wavelike Spectrum Classical View s Quantized energy Photon Quantum-mechanical Views wave Perpendicular Identical spectrum C=λν λ increase ν decrease photon What is a photon? The unit of light A kind of particle A group or packet of energy Light interactions with solids •Incident light is either reflected, absorbed, or transmitted: Io=IT+IA+IR Light interactions with solids •Optical classification of materials: Electronic polarization Phenomenon: Causes: •rapidly fluctuating electric field •interaction between electric field and electron cloud Consequences: •Some of the radiation energy may be absorbed •Light waves are retarded in velocity as they pass through the medium Electron transitions Two states: ground state and excited state Two processes: •Absorption •Emission Specific ΔE’s: ΔE =hν Contents Electromagnetic Radiation Light Interaction With Solids Electronic Polarization Electron Transitions Thank you !