11_Feb 26_Lasers, colors

Today: Colors, Lasers, Reflection

Energy efficient “Compact Fluorescent” lighting

Quiz 4

Which color star would be the hottest?

A) RedB) YellowC) OrangeD) BlueE) White

Which color star would be the hottest?

A) RedB) YellowC) OrangeD) BlueE) White

To get glowing red light, peak radiation would be in infrared region

Visible range

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)

A. Incandescent lightingB. Fluorescent lightingC. Combustion lighting (flame)

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)

A. Incandescent lightingB. Fluorescent lightingC. 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

Homework problem introduction

1. Incandescent – Blackbody radiationColor is yellow (cooler than the sun)Most photons are infrared

2. Fluorescent – Electrons excite mercury, which emits UV photons.UV photons absorbed by phosphors, which fluoresce in visible

3. Incandescent “wastes” lots of photons in the IR.

Visible range

Images:wikipedia

Color perception is a very complicated mixture of physics and physiology

Blackbody spectrum color simulationhttp://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 boothhttp://www.gelighting.com/na/business_lighting/education_resources/learn_about_light/color_lamp.htm

Think of the acoustic parallel and a “synthesizer”

DEMOS

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)

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”

How does a laser work? First:http://www.colorado.edu/physics/PhysicsInitiative/Physics2000/lasers/lasers2.html

How does a laser work?

Light Amplification by Stimulated Emission of Radiation

1. Requires some source of energyConservation of energy still applies!

2. Requires an atom with at least 3 energy states(Population inversion)

3. Requires a “resonant cavity”Very similar to the acoustic “flame tube” demo

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).

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

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

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

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

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

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 incidenceRefraction: Imagine the wave as a two wheeled

cart encountering a boundary

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

TIR enables a special surface microscopy technique

Air

glass

“Evanescent” WaveExcite fluorescence in cell with evanescent wave

www.olympusamerica.comRed = TIRFGreen = regular