Jerry Joseph Wilmink

1
Light and Lasers

• Jerry Joseph Wilmink
• M.S. (Ph.D. Candidate)
• Scientist-in-the-Classroom Program
• Rose Park Middle School
• Monday, February 12, 2006- 445-700 PM
• Vanderbilt University, Nashville, TN 37235

2
Think, Pair, Share- YELLOW SHEET

• Read/think about each question for 30 seconds
• Pair up with person next to you and discuss for
  30 seconds
• Share with the class

3
Pre-Questionnaire

• Light is referred to as _______________ radiation
  which behaves both like a ____________ and a
  ____________.

4
Pre-Questionnaire

• The __________ or ___________of visible light is
  perceived by humans as the color of the light.

5
Pre-Questionnaire

• A typical human eye will respond to wavelengths
  ranging from _______ to ________ nm

6
Pre-Questionnaire

• When light hits objects what 4 things can happen
  to it
• _______________
• _______________
• _______________
• _______________

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Light Humble Beginnings..

• Genesis
• 1 First God made heaven earth
• 2 The earth was without form and void, and
  darkness was upon the face of the deep and the
  Spirit of God was moving over the face of the
  waters.
• 3 And God said, "Let there be light" and there
  was light.
• 4 And God saw that the light was good and God
  separated the light from the darkness.
• 5 God called the light Day, and the darkness he
  called Night.

8
Light Humble Beginnings..

• Columbus Discovers America in 1492
• Abstract by Bartolome de las Casas in the 1530s.
  Las Casas was an historian and Columbus's
  biographer who had access to the original journal
  of the voyage. We join Columbus's account as his
  expedition approaches the islands of the Bahamas.
  Throughout the account, Columbus refers to
  himself in the third person as the "Admiral"
• Date Thursday October 11, 1492
• After the Admiral (Columbus) had spoken he saw
  the light once or twice, and it was like a wax
  candle rising and failing. It seemed to few to be
  an indication of land but the Admiral made
  certain that land was close. When they said the
  Salve, (Salve Regina) which all the sailors were
  accustomed to sing in their way, the Admiral
  asked and admonished the men to keep a good
  look-out on the forecastle, and to watch well for
  land and to him who should first cry out that he
  saw land, he would give a silk doublet, besides
  the other rewards promised by the Sovereigns,
  which were 10,000 maravedis to him who should
  first saw it. At two hours after midnight the
  land was sighted at a distance of two leagues.

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Poem about Light Hope

• J.R. Miller
• Brave Admiral, say but one good word
• What shall we do when hope is gone?
• The words leapt like a leaping sword
• Sail on! Sail on! Sail on! And on!
• The, pale and worn, he kept his deck
• And peered through the darkness. Ah! That night
• Of all dark nights! And then a speck----
• A light! A light! A Light ! A light!
• It grew, a starlit flag unfurled!
• It grew to be Times burst of dawn
• He gained a world he gave that world
• Its grandest lesson On! Sail on!

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Outline

• Introduction to Light
• Sources
• Definition
• Examples of EM
• Properties of Light
• Wave Speed, Refraction, Specular Reflection
• Optics
• Particle Diffuse Refl, Scattering Absorption
• Lamps vs. Laser Light
• Lasers in the Hospital
• How lasers work?

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1a) Light Sources
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1b) Light Definition Make up your mind? Wave or
particle

• Light is electromagnetic radiation with any
  wavelength and is defined by having elementary
  particle called photons
• Wave-particle duality
• 1. Wave properties
• 2. Particle/photon properties
• 3 basic dimensions
• Intensity (or amplitude)? brightness
• Frequency (or wavelength)? color of light
• Polarization (or angle of vibration)

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1c)Examples of EM Radiation
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2a) Properties of Visible Light

• Wavelength (?) size in nm
• Frequency (f) waves/second ltHzgt
• Light photons have energy (quanta)
• Planks constant (h) 6.63 10-34 ltJ x sgt
• Energy h f
• F c/ ?, E hc/ ?

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2b) Speed of Light SLOW DOWN!!!
Earth

• Speed of light in vacuum
• 300,000,000 meters/second
• Speed of light in dense materials
• Reduced index of refraction (n)

3.84 x108 m
n x v c
Vacuum (n1) v c
Water (n1.33) v c/1.33
Moon
Glass (n1.46) v c/1.46
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3a) Optics light interacting with matter
1. Incoming Light
2. Reflection/unscattered (specular, mirror-like)
F light F material Electrons accept E vibrate
3. Transmitted
4. Refraction/Scattering (diffuse)
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3a) Reflection specular

• Definition
• Change in direction of WAVE front at interface
  between two dissimilar media so the wave front
  returns into the medium from which it originated
• Types of Reflection
• Specular (mirror-like)
• Diffuse (retain only energy)

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3b) Total Internal Reflection

• Defn
• light strikes a medium boundary at a steep angle
• If the refractive index is lower on the other
  side of the boundary no light can pass through,
  so effectively all of the light is reflected.
• The critical angle is the angle of incidence
  above which the total internal reflection occurs.

19
3b) TIR in Optical Fibers
20
3b) Biomedical Applications
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3c) Index of Refraction Velocity

• Definition
• light enters a medium keeps the same frequency
  changes it wavelength
• E hf hc/wavelength ? f c/wavelength
• Remember n c/v, High n low v
• Snells Law
• Equation n1 sin (?1) n2 sin (?2)
• Football field example

22
3c) Example of Refraction

• Refraction of light waves in water
• Explanation
• Dark rectangle actual position pencil
• Light rectangle apparent position pencil
• X looks like at Y
• Change in direction of a wave due to a change in
  its speed

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3d) Absorption
Beer-Lambert Law
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4) Tissue Absorption
NdYAG
ErYAG
Argon
CO2
HoYAG
100000
105
10-4
10000
10-3
1000
100
10-2
10-1
10
optical penetration Depth d mm
Blood
Absorption coefficient ma mm-1
1
100
Water
0.1
101
Melanin
0.01
102
0.001
103
0.0001
104
0.1
1
2
3
10
Wavelength mm
25
3d) Scattering

• Definition
• Process where light or moving particles are
  forced to deviate from a straight trajectory by
  one or more localized non-uniformities in the
  medium through which it passes
• 2 General Types Reflections
• diffuse reflections
• unscattered reflections, specular (mirror-like)
• 3 Types of Scattering
• Rayleigh- sky blue, ? dependent, blue light
  scattered 4x more red
• Mie- white appearance of clouds
• Non-selective-

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3d) Todays Scattering Example
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4) LASER Section

• Light
• Amplification by
• Stimulated
• Emission
• Radiation

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4) History of Lasers
1917 Einstein, Stimulated emission possible 1928
Ladenburg, Experimental proof of stimulated
emission Kopfermann 1953 Weber Invention of
MASER Gordon Prokorov 1960 Maiman Invention of
Ruby laser 1961 Yavan HeNe-Laser 1961
Goldman First medical laser application 1962
Hall Semiconductor laser (Gallium arsenide) 1964
Patell CO2 Laser
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4) The Laser Inventors
Dr. T H Maiman with the first ruby laser
Arthur L Schawlow, 1981 Nobel Prize for Laser
Spectroscopy
... when the first lasers were operated, I and
other scientists close to the research were
surprised at how easy it turned out to be. We had
assumed that, since lasers had never been made,
it must be very difficult. But once you knew how,
it was not at all difficult. Mostly what had been
lacking were ideas and concepts.

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How are LAMPS different from LASER LIGHT?
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LAMP
LASER
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4) How Lasers Work?
1. Atom smallest form of an element -Nucleus
Electron Cloud
2. Heat electron up - Via heat, electricity,-Ex.
Toaster turns red
3. Laser-Atom Connection - LASER Light
amplification by stimulated emission of
radiation - Emitted photon ? specific wavelength
Emission of a Light Photon
Color Wavelength
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What are lasers used for?

• CD/DVD players
• Laser printers
• Entertainment Purposes
• Laser pointers
• Checkout line at supermarket
• Factory- to cut metal and glass
• Hang pictures
• Accurate alignment

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Lasers at Vanderbilt Hospital

• History
• Clinical Diagnostic Applications
• Ophthalmology
• Dermatology
• Cosmetic Surgery
• Urology
• Neuroscience

Versatile tool?
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4) Why do Lasers Rule in Medicine
UV ? 260 nm
VIS ? 556 nm
IR ? 2.94µm

• Tissue components
• Biomolecules
• Chrom color
• Chromophores absorb light
• Lasers use 1 wavelength
• Target specific chromophores

IR ? 6.45µm
DNA
Hemoglobin
Water
Protein
Anderson Science 1983, Vogel Chem Rev 2003
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Wavelength
NdYAG
ErYAG
Argon
CO2
HoYAG
100000
105
10-4
10000
10-3
1000
100
10-2
10-1
10
optical penetration Depth d mm
Blood
Absorption coefficient ma mm-1
1
100
Water
0.1
101
Melanin
0.01
102
0.001
103
0.0001
104
0.1
1
2
3
10
Wavelength mm
37
Research Application? Use light 2 ways.
Luciferase
Firefly
Heat Shock Protein