1. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 1 Bruce Mayer, PE Engineering-45: Materials of Engineering Bruce Mayer, PE Licensed Electrical & Mechanical Engineer BMayer@ChabotCollege.edu Engineering 45 Optical Properties

2. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 2 Bruce Mayer, PE Engineering-45: Materials of Engineering Learning Goals – Optical Props  Learn How Light and Solid Materials Interact  Why materials have characteristic colors  Why some materials transparent and others not  Optical applications: Luminescence Photoconductivity Solar Cell Optical Fiber Communications

3. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 3 Bruce Mayer, PE Engineering-45: Materials of Engineering Properties of Solid Materials  Mechanical: Characteristics of materials displayed when forces are applied to them.  Physical: Characteristics of materials that relate to the interaction of materials with various forms of energy.  Chemical: Material characteristics that relate to the structure of a material.  Dimensional: Size, shape, and finish

4. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 4 Bruce Mayer, PE Engineering-45: Materials of Engineering Material Properties Chemical Physical Mechanical Dimensional Composition Melting Point Tensile propertiesStandard Shapes Microstructure Thermal Toughness Standard Sizes Phases Magnetic DuctilitySurface Texture Grain Size Electrical FatigueStability Corrosion Optical HardnessMfg. Tolerances Crystallinity Acoustic Creep Molecular Weight Gravimetric Compression Flammability

5. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 5 Bruce Mayer, PE Engineering-45: Materials of Engineering ElectroMagnetic Radiation  Energy associated with Light, Radio Signals, X-rays and Others is Transmitted as ElectroMagnetic (EM) Radiation (EMR)  Electromagnetic radiation Transmits energy in the form of a Sinusoidal wave Which Contains ELECTRICAL & MAGNETIC Field-Components  The EM waves Travel in Tandem, and are perpendicular to Each Other The Direction Of Propagation

6. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 6 Bruce Mayer, PE Engineering-45: Materials of Engineering The EM Spectrum  EM Waves Cover a Wide Range of WAVELENGTHS,, and FREQUENCIES, : miles→femtometers  “Light” is generally divided into Three Segments UltraViolet: 0.001→0.35 µm –NOT Visible, High in Energy Visible: 0.35→0.7 µm –A VERY Small Slice of the EM spectrum InfraRed: 0.7-1000 µm –Not Visible; carries “sensible” energy (heat)

7. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 7 Bruce Mayer, PE Engineering-45: Materials of Engineering EM Radiation Quantified  All EM Waves Travel at the Speed of Light, c  c is a Universal Constant with a value of 300 Mm/s (186 000 miles/sec)  c is related to the Electric & Magnetic Universal Constants Where (Recalling From Previous Lectures) –  0  ELECTRIC Permittivity of Free Space (a vacuum) –µ 0  MAGNETIC Permeability of Free Space (a vacuum)

8. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 8 Bruce Mayer, PE Engineering-45: Materials of Engineering EM Radiation Quantified  The Wavelength and Frequency of EM waves are related thru c Where –  WaveLength in meters per cycle –  Frequency in Hertz (cycles/sec)  EM radiation has a Wave↔Particle Duality  The Energy, E, of a Light Particle Where h  Planck’s Constant (6.63x10 -34 J-s)  h is the PHOTON Energy

9. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 9 Bruce Mayer, PE Engineering-45: Materials of Engineering EM-Solid Interaction  Consider EM Radiation with Intensity I 0 (in W/m 2 ) Impinging on a Solid  The EM-Solid interaction Alters the incident Beam by 3 possible Phenomena The EM Beam can be –Reflected –Absorbed –Transmitted

10. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 10 Bruce Mayer, PE Engineering-45: Materials of Engineering EM-Solid Interaction cont  Mathematically  An Energy Balance on the Solid: E-in = E-reflected + E-absorbed + E-transmitted Where all the I K are Intensities in W/sq-m  Now Divide E-Balance Eqn by I 0

11. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 11 Bruce Mayer, PE Engineering-45: Materials of Engineering EM-Solid Interaction cont.2 Transparent → –T >> A+R –Light Not Scattered Translucent→ –T > A+R –Light Scattered Where: –R  REFLECTANCE (I R /I 0 ) –A  ABSORBANCE (I A /I 0 ) –T  TRANSMITTANCE (I T /I 0 )  Using R, A, T, Classify EM-Solid Behavior Opaque → T = 0

12. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 12 Bruce Mayer, PE Engineering-45: Materials of Engineering Metals – Optical Absorption  Metals Interact with Light Thru QUANTIZED Photon Absorption by Electrons Energy of electron Incident photon filled states unfilled states  E = h required I o of Energy h  Metals have Very Closely Spaced e- Energy Levels Thus Almost ALL incident Photons are ABSORBED within about 100 nm of the surface

13. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 13 Bruce Mayer, PE Engineering-45: Materials of Engineering Metals – Optical Reflection  The Absorbed Energy is ReEmitted by e- “falling” back to Lower Energy states  Since Metals have Very Closely Spaced e- Energy Levels The Light is emitted at many ’s re-emitted photon from material surface Energy of electron filled states unfilled states  E IRIR “conducting” electron Thus Outgoing Light Looks About the Same as Incoming Light → High Reflectance

14. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 14 Bruce Mayer, PE Engineering-45: Materials of Engineering Light Absorbtion/Reflection  Amount of NON-Reflected Light Absorbed by a Matl  For normally incident light passing into a solid having an index of refraction n:  = absorption coefficient, cm -1 = sample thickness, cm = NonReflected incident light intensity = transmitted light intensity

15. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 15 Bruce Mayer, PE Engineering-45: Materials of Engineering Metals - Colors  Metals also ABSORB Some Photons Dissipated as heat  Metals that Absorb few, or in broad-spectrum, reflect “WHITE” Light and Appear Silvery  Some Metals absorb Preferentially, and the Reflected Light is Colored due the absence of the Absorbed light e.g., Cu Absorbs in the Violet-Blue; leaving Reflected light rich in Orange-Red Cu Bar Sn-Plated Cu Bar

16. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 16 Bruce Mayer, PE Engineering-45: Materials of Engineering Total Transmission  Combining External and Internal Reflection, along with Beer’s Absorbtion Yields the TOTAL Transmission Eqn

17. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 17 Bruce Mayer, PE Engineering-45: Materials of Engineering Total-T Example  For the Situation at Right Determine the thickness, d 77, that will produce a total Transmittance of 77%  From Tab 21.1 Find Pyrex n s = 1.47  Next find R using Eqn (21.13) Pyrex 23 mm

18. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 18 Bruce Mayer, PE Engineering-45: Materials of Engineering Total-T Example  Recall total Transmission Eq  Now Solve for β Pyrex 23 mm

19. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 19 Bruce Mayer, PE Engineering-45: Materials of Engineering Total-T Example  Thus  Solving Total-T Eqn for the length  Then d 77 Pyrex 23 mm

20. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 20 Bruce Mayer, PE Engineering-45: Materials of Engineering NonMetals – Selective Absorb.  In The Case of Materials with “Forbidden” Gaps in the Band Structure, Absorption Occurs only if h >E gap  For These Materials there is Very little ReEmission The Material Color Depends on the Width of the BandGap incident photon energy h Energy of electron filled states unfilled states E gap I o blue light: h  3.3 ev red light: h  1.8 ev

21. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 21 Bruce Mayer, PE Engineering-45: Materials of Engineering Color Cases – BandGap Matls  E gap < 1.8 eV ALL Visible Light Absorbed; Solid Appears Gray or Black in Color –e.g., Si with E gap = 1.1 eV  E gap > 3.3 eV NO Visible Light Absorbed; Solid Appears Clear and Transmissive –e.g., Diamond E gap = 5.45 eV, SiO 2 E gap = 8-9 eV  1.8 eV < E gap < 3.3 eV Some Light is absorbed and Material has a color

22. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 22 Bruce Mayer, PE Engineering-45: Materials of Engineering NonMetal Colors  Color determined by sum of frequencies transmitted light re-emitted light from electron transitions  e.g., Cadmium Sulfide (CdS) E gap = 2.4eV Absorbs higher energy visible light (blue, violet),  CdS Red/yellow/orange is transmitted and gives it this color

23. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 23 Bruce Mayer, PE Engineering-45: Materials of Engineering NonMetal Colors cont.  Ex: Ruby = Sapphire (Al 2 O 3 ) + 0.5-2 at% Cr 2 O 3 Sapphire is colorless (i.e., E gap > 3.1eV)  adding Cr 2 O 3 alters the band gap blue light is absorbed yellow/green is absorbed red is transmitted  Result: Ruby is deep Red in color

24. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 24 Bruce Mayer, PE Engineering-45: Materials of Engineering Wavelength vs. Band Gap  Example: What is the maximum wavelength absorbed by Ge?  Find Ge BandGap: E g = 0.67 eV Thus Need E photon = hc/λ max ≥ E g  Use the Photon Energy Eqn:

25. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 25 Bruce Mayer, PE Engineering-45: Materials of Engineering Light Refraction  When Light Encounters a Matter-Containing Environment, it SLOWS DOWN Due to Interaction with Electrons + no transmitted light transmitted light + electron cloud distorts  Define the INDEX of REFRACTION, n

26. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 26 Bruce Mayer, PE Engineering-45: Materials of Engineering Light Refraction cont  The slowing of light in a Non-Vacuum Medium Results in Refraction, or Bending of the light Path  Light Refracts per Snell’s Law :

27. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 27 Bruce Mayer, PE Engineering-45: Materials of Engineering Refraction Physics  Recall  Thus n  Now the relations for v and c Where ε & µ are respectively the Permittivity & Permeability of the Material  Now Recall  Most Matls are NOT magnetic → µ r  1 So  e.g. Germanium n = 3.97 → n 2 = 15.76  r = 16.0 (very close)

28. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 28 Bruce Mayer, PE Engineering-45: Materials of Engineering Application  Luminescence  Based on EM Induced e − excitation, and then Relaxation with Broad-Spectrum h Emission  e.g. fluorescent lamps emitted light h 1 + h 2 +... Energy of electron filled states unfilled states E gap Re-emission Occurs Incident Radiation h 0 Electron Excitation Energy of electron filled states unfilled states E gap UV radiation coating e.g.;  -alumina, doped w/ Europium “white” light glass

29. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 29 Bruce Mayer, PE Engineering-45: Materials of Engineering Application  PhotoConduction  h Absorption by NO-Junction SemiConductors results in the Elevation of an e- to the Conduction Band Where it Can Carry an E-Field Driven Current  e.g. Cadmium Sulfide semi conductor: Energy of electron filled states unfilled states E gap + - A. No incident radiation: little current flow Incident radiation Energy of electron filled states unfilled states E gap Conducting e- + - B. Incident radiation: Increased current flow

30. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 30 Bruce Mayer, PE Engineering-45: Materials of Engineering Application  Si Solar Cell  Recall The PN Junction  Operation for Si Cell: An incident PHOTON produces HOLE-ELECTRON pair. Typically 0.5-0.7 V potential –Theoretical Max = 1.1 V (E gap ). Current INCREASES with INCREASED Light INTENSITY –Need to Minimize Reflectance n-type Si p-type Si p-n junction B-dopedSi B hole P Si conduction electron P-dopedSi n p + E -

31. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 31 Bruce Mayer, PE Engineering-45: Materials of Engineering Application – Heat Mirror  Natural SunLight is Very Pleasant However, In Sunny Climes Windows that Admit Visible Light ALSO transmit InfraRed EM radiation that Heats the Building; increasing AirConditioning costs  Soln → “Heat” Mirror Window

32. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 32 Bruce Mayer, PE Engineering-45: Materials of Engineering Application – Heat Mirror cont  A Perfect Heat Mirror Would Transmit 100% of EM radiation (light) in the visible 350-700 nm Wavelength range Reflect 100% of EMR over 700 nm  Heat Mirror Windows are Constructed from thin-film coated “window glass”  HM Film Stack → dielectric / metal / dielectric (D/M/D) e.g., 300Å TiO 2 / 130Å Ag / 300Å TiO 2 http://www.cerac.com/pubs/cmn/cmn6_4.htm

33. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 33 Bruce Mayer, PE Engineering-45: Materials of Engineering All Done for Today The Solar Spectrum

34. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 34 Bruce Mayer, PE Engineering-45: Materials of Engineering WhiteBoard Work  Derive Eqns 21.18 –Thick, Strongly Absorbing Medium of thickness d 21.19 –Weakly Absorbing (transparent) medium with Reflection, R, and thickness d

35. BMayer@ChabotCollege.edu ENGR-45_Lec-13_Optical_Properties.ppt 35 Bruce Mayer, PE Engineering-45: Materials of Engineering Heat Mirror Hot Miror (Heat Reflecting) What - These "hot mirror" filters transmit the visible spectrum and reflect the infrared. At any specified angle of incidence, the average transmission is more than 93% from 425 to 675 nm. The average reflectance of our standard Hot Mirror is more than 95% from 750 to 1150 nm. Extended Hot Mirror: The average reflectance is more than 90% from 750 to 1600 nm. Long IR Hot Mirror The average reflectance is more than 90% from 1700 to 3000 nm Cold Mirror (Heat Transmitting) These "cold mirror" filters reflect the visible spectrum and transmit heat (infrared). At any specified angle of incidence, average reflectance is more that 95% from 450 to 675 nm. Transmission is more than 85% from 800 to 1200 nm.