11_Feb 26_Lasers, colors

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Fluorescent lighting, effect on color perception, lasers fundamentals, reflection, refraction, total internal reflection

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11_Feb 26_Lasers, colors

  1. 1. Today: Colors, Lasers, Reflection Energy efficient “ Compact Fluorescent” lighting
  2. 2. Quiz 4
  3. 3. Which color star would be the hottest? <ul><li>Red </li></ul><ul><li>Yellow </li></ul><ul><li>Orange </li></ul><ul><li>Blue </li></ul><ul><li>White </li></ul>
  4. 4. Which color star would be the hottest? <ul><li>Red </li></ul><ul><li>Yellow </li></ul><ul><li>Orange </li></ul><ul><li>Blue </li></ul><ul><li>White </li></ul>
  5. 5. To get glowing red light, peak radiation would be in infrared region Visible range
  6. 6. Clicker Question—Lighting efficiency <ul><li>Which of the following is the most energy efficient way of light the home (in terms of portion of energy converted to visible light) </li></ul><ul><li>Incandescent lighting </li></ul><ul><li>Fluorescent lighting </li></ul><ul><li>Combustion lighting (flame) </li></ul>
  7. 7. Clicker Question—Lighting efficiency <ul><li>Which of the following is the most energy efficient way of light the home (in terms of portion of energy converted to visible light) </li></ul><ul><li>Incandescent lighting </li></ul><ul><li>Fluorescent lighting </li></ul><ul><li>Combustion lighting (flame) </li></ul>Or using natural sunlight is even better! (though you could argue about “efficiency”) We will have a homework question this week to lead you through an explanation of why this is true
  8. 8. Homework problem introduction <ul><li>Incandescent – Blackbody radiation Color is yellow (cooler than the sun) Most photons are infrared </li></ul><ul><li>Fluorescent – Electrons excite mercury, which emits UV photons. UV photons absorbed by phosphors, which fluoresce in visible </li></ul><ul><li>Incandescent “wastes” lots of photons in the IR. </li></ul>Visible range Images:wikipedia
  9. 9. Color perception is a very complicated mixture of physics and physiology <ul><li>Blackbody spectrum color simulation http://www.shodor.org/refdesk/Resources/Models/BlackbodyRadiation </li></ul><ul><li>Incandescent (Blackbody) radiation has smooth spectrum, similar to sun (but yellower) </li></ul><ul><li>Fluorescent lighting must try to synthesize white light by adding together various fluorescence spectra </li></ul>http://www.gelighting.com/na/business_lighting/education_resources/learn_about_light/distribution_curves.htm GE Interactive color booth http://www.gelighting.com/na/business_lighting/education_resources/learn_about_light/color_lamp.htm Think of the acoustic parallel and a “synthesizer” DEMOS
  10. 10. Brainstorming--Lasers <ul><li>Let’s think of lasers we know of, and what kinds of unique properties they have </li></ul><ul><li>Lasers: Laser to shoot missiles down; Lasik lasers; optical tweezers; CD/DVD/Blue-ray players; laser pointers; laser printers /copiers; frickin’ shark lasers; laser hair removal lasers; dog laser pointers; bar code scanners; laser tag; surgical lasers (excimer, etc.); metal machining lasers; engraving lasers; wood burning lasers; tatoo removal lasers; laser sights; diamond cutting? </li></ul><ul><li>Properties: spectral color (monochromatic); straight lines (more focused “collimated”); accuracy (easy to direct); accuracy (easy to focus to small spot); (coherency) </li></ul>
  11. 11. Lasers…important qualities <ul><li>Monochromatic – photons all have very close to the same frequency (color) Let’s check this out with diffraction gratings! </li></ul><ul><li>Collimated —low divergence angle (usually) </li></ul><ul><li>Coherent —all photons have the same phase (we won’t emphasize this for now) </li></ul><ul><li>Laser shares some properties with acoustical “pure tone” </li></ul>
  12. 12. How does a laser work? First: http://www.colorado.edu/physics/PhysicsInitiative/Physics2000/lasers/lasers2.html
  13. 14. How does a laser work? <ul><li>L ight A mplification by S timulated E mission of R adiation </li></ul><ul><li>Requires some source of energy Conservation of energy still applies! </li></ul><ul><li>Requires an atom with at least 3 energy states (Population inversion) </li></ul><ul><li>Requires a “resonant cavity” Very similar to the acoustic “flame tube” demo </li></ul>
  14. 15. Laser pointers <ul><li>Red laser pointer – simple diode laser, fairly cheap </li></ul><ul><li>Green laser pointer – complicated and expensive! </li></ul><ul><li>infrared diode laser “pumps” a second laser, which emits lower frequency infrared. TWO of these infrared photons combine to pump a green laser (frequency doubles). </li></ul>
  15. 16. Light emitting diodes (LEDs) and Laser Diodes <ul><li>LEDs convert electric current directly into photons (opposite of photovoltaic) </li></ul><ul><li>Make a resonant cavity, crank up the power and you have a “diode laser!” </li></ul><ul><li>Diode Lasers and LEDs are becoming very useful in the real world. E.g., laser pointers, CD players, traffic lights, etc. </li></ul>First: what are solar cells? http://www.youtube.com/watch?v=napVP6jAZxM&feature=related
  16. 17. Next we’ll start talking about reflection and refraction http://www.youtube.com/watch?v=_6LsXA_FJIE&feature=related A really fun introduction to the subject! The archer fish
  17. 18. Clicker Question—Reflection <ul><li>Which of the following diagrams most likely represents the reflection of a ray of visible light from a high quality silver mirror? (The mirror is convex) </li></ul>A B C
  18. 19. Clicker Question—Reflection <ul><li>Which of the following diagrams most likely represents the reflection of a ray of visible light from a high quality silver mirror? (The mirror is convex) </li></ul>A B C Reflection: Angle of reflection = angle of incidence
  19. 20. Clicker Question <ul><li>Which of the following diagrams best represents what happens when a red light wave encounters an air / diamond interface? </li></ul>A B C Air Diamond
  20. 21. Clicker Question -- Refraction <ul><li>Which of the following diagrams best represents what happens when a red light wave encounters an air / diamond interface? </li></ul>A B C Air Diamond Reflection: Angle of reflection = angle of incidence Refraction: Imagine the wave as a two wheeled cart encountering a boundary
  21. 22. Total internal reflection <ul><li>Imagine what happens when a ray of light is in a higher index of refraction material… </li></ul>Air glass “ Evanescent” Wave Total internal reflection Total internal reflection a key to fiber optics! -> demo
  22. 23. TIR enables a special surface microscopy technique Air glass “ Evanescent” Wave Excite fluorescence in cell with evanescent wave www.olympusamerica.com Red = TIRF Green = regular

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