Transcript Physics 123 “Majors” Section Unit 1

Announcements 11/19/12
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Prayer
Quick demo: diffraction from a hair
Lab 10 due tomorrow
Exam 3 starts Monday after break, goes through Saturday
Exam 3 review session: Monday after break, 4:30-6 pm,
this room
Final exam: in Testing Center, M-Th week of finals
Frank &
Ernest
From warmup
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Extra time on?
a. It would be nice to talk about the last parts of
Chapter 10, it was hard to understand his
explanation of the [wave]plates because it was a
lot at once.
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Other comments?
a. Is there any simple way to describe the quantum
mechanics of lasers??? I want to know how they
work.
From warmup
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Which of the following is NOT true of the 3D
“wave vector”?
a. Its magnitude is equal to 2π/λ.
b. For every point inside a plane wave, it
points the same direction.
c. For every point inside a spherical wave, it
points the same direction.
d. It tells us which way the wave is going.
e. In 1D it reduces to the wave number k.
Waves in 3-dimensions
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Plane waves
a. polarization
Wave vector
a. direction of wave
General Form
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E  E0pˆ cos k x x  k y y  k z z  t
Specific Example
E  E0
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Spherical waves
1
 xˆ + yˆ  cos  kz  t 
2
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Student-designed problem: Transverse Wave
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What direction do you want the wave to be
traveling in?
What direction do you want the wave to be
oscillating in?
What wavelength do you want the wave to have?
What do you want the wave’s amplitude to be?
What frequency (or velocity) do you want the wave
to have?
What do you want the overall phase of the wave to
be?
Clicker question
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How many lasers do you have in your
house/apartment?
a. 0
b. 1
c. 2
d. 3
e. 4+
From warmup
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Name one cool thing about lasers that you didn't know prior to this reading
assignment.
a.
Lasers can help cool down temperatures to less than one millionth of a
degree above absolute zero. (5 students)
b.
The number which shocked me the most was the specificity of
wavelength – that 99.99999999 percent of all light would be filtered
away. (4 students)
c.
It works by quantum mechanics. (3 students)
d.
they can be focused more than regular light which make them useful for
things like surgery or welding (2 students)
e.
I didn't know that some of the qualities of lasers cannot possibly be
mimicked by conventional light bulbs. -"higher order coherences“ ( 2
students)
f.
Lasers are coherent sources of light.
g.
Laboratory lasers produce light with wavelength variations of only 10^-6
nm
h.
They are extremely efficient in regards to energy use.
i.
they are used to read and write CD's
j.
It was really cool learning more how they are made…
k.
I watched Megamind on Friday, and wondered why Titan's laser eyes
were melting and burnign the city away. Now I know why and he must
have had powerful eyes.
Lasers
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What makes a laser
special?
a. Single wavelength
b. Intense
c. Collimated
d. Coherence (spatial,
temporal)
Actual laser spectrum
is over 100 narrower
than the width of the
red line
Laser spectrum
Blackbody spectrum
Image & list from Wikipedia
Lasers
Stimulated
Emission Emission
Absorption
Energy
(light)
(light,
electrical,
etc.)
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Principal components:
1.
2.
3.
4.
5.
Gain medium
Laser pumping energy
High reflector
Output coupler
Laser beam
light
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Green laser pointer
More Wikipedia
5. laser beam
3. high
reflector
1. gain medium
(Nd:YVO4 crystal)
2. laser pumping energy
(808 nm LED beam)
4. output
coupler
More Wikipedia
Circular Polarization
Remember these pictures?
Blue & green both represent
electric fields.
Ex out of phase with Ey.
Pictures from Wikipedia
Optical Retarders, aka “Wave plates”
Calcite crystal:
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Quartz, SiO2: no = 1.544, ne = 1.553
Calcite, CaCO3: no = 1.658, ne = 1.486
Pictures from Wikipedia
Optical Modulators
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Electro-optic modulator
Acousto-optic modulator
AOM
EOM
Field changes
vertical index of
refraction
www.newport.com
wikipedia