11_Feb 26_Lasers, colors
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11_Feb 26_Lasers, colors

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

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

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  • 1. Today: Colors, Lasers, Reflection Energy efficient “ Compact Fluorescent” lighting
  • 2. Quiz 4
  • 3. Which color star would be the hottest?
    • Red
    • Yellow
    • Orange
    • Blue
    • White
  • 4. Which color star would be the hottest?
    • Red
    • Yellow
    • Orange
    • Blue
    • White
  • 5. To get glowing red light, peak radiation would be in infrared region Visible range
  • 6. Clicker Question—Lighting efficiency
    • Which of the following is the most energy efficient way of light the home (in terms of portion of energy converted to visible light)
    • Incandescent lighting
    • Fluorescent lighting
    • Combustion lighting (flame)
  • 7. Clicker Question—Lighting efficiency
    • Which of the following is the most energy efficient way of light the home (in terms of portion of energy converted to visible light)
    • Incandescent lighting
    • Fluorescent lighting
    • Combustion lighting (flame)
    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. Homework problem introduction
    • Incandescent – Blackbody radiation Color is yellow (cooler than the sun) Most photons are infrared
    • Fluorescent – Electrons excite mercury, which emits UV photons. UV photons absorbed by phosphors, which fluoresce in visible
    • Incandescent “wastes” lots of photons in the IR.
    Visible range Images:wikipedia
  • 9. Color perception is a very complicated mixture of physics and physiology
    • Blackbody spectrum color simulation http://www.shodor.org/refdesk/Resources/Models/BlackbodyRadiation
    • Incandescent (Blackbody) radiation has smooth spectrum, similar to sun (but yellower)
    • Fluorescent lighting must try to synthesize white light by adding together various fluorescence spectra
    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. Brainstorming--Lasers
    • Let’s think of lasers we know of, and what kinds of unique properties they have
    • 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?
    • Properties: spectral color (monochromatic); straight lines (more focused “collimated”); accuracy (easy to direct); accuracy (easy to focus to small spot); (coherency)
  • 11. Lasers…important qualities
    • Monochromatic – photons all have very close to the same frequency (color) Let’s check this out with diffraction gratings!
    • Collimated —low divergence angle (usually)
    • Coherent —all photons have the same phase (we won’t emphasize this for now)
    • Laser shares some properties with acoustical “pure tone”
  • 12. How does a laser work? First: http://www.colorado.edu/physics/PhysicsInitiative/Physics2000/lasers/lasers2.html
  • 13.  
  • 14. How does a laser work?
    • L ight A mplification by S timulated E mission of R adiation
    • Requires some source of energy Conservation of energy still applies!
    • Requires an atom with at least 3 energy states (Population inversion)
    • Requires a “resonant cavity” Very similar to the acoustic “flame tube” demo
  • 15. Laser pointers
    • Red laser pointer – simple diode laser, fairly cheap
    • Green laser pointer – complicated and expensive!
    • 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).
  • 16. Light emitting diodes (LEDs) and Laser Diodes
    • LEDs convert electric current directly into photons (opposite of photovoltaic)
    • Make a resonant cavity, crank up the power and you have a “diode laser!”
    • Diode Lasers and LEDs are becoming very useful in the real world. E.g., laser pointers, CD players, traffic lights, etc.
    First: what are solar cells? http://www.youtube.com/watch?v=napVP6jAZxM&feature=related
  • 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
  • 18. Clicker Question—Reflection
    • 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)
    A B C
  • 19. Clicker Question—Reflection
    • 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)
    A B C Reflection: Angle of reflection = angle of incidence
  • 20. Clicker Question
    • Which of the following diagrams best represents what happens when a red light wave encounters an air / diamond interface?
    A B C Air Diamond
  • 21. Clicker Question -- Refraction
    • Which of the following diagrams best represents what happens when a red light wave encounters an air / diamond interface?
    A B C Air Diamond Reflection: Angle of reflection = angle of incidence Refraction: Imagine the wave as a two wheeled cart encountering a boundary
  • 22. Total internal reflection
    • Imagine what happens when a ray of light is in a higher index of refraction material…
    Air glass “ Evanescent” Wave Total internal reflection Total internal reflection a key to fiber optics! -> demo
  • 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