General Properties of Light
Light as a wave
• Speed
• Wave properties:
wavelength, frequency, period,
speed, amplitude, intensity
• Electromagnetic wave
EM Spectrum
4 x 10-11
4 x 10-7
3 x 104
Long waves
102
104
4 x 10-3
3 x 10-4
3
Radio waves
106
108
4 x 101
3 x 10-8
Infrared
1010
1012
4 x 105
1014
Ultraviolet
1016
Visible Light
Energy (eV)
3 x 10-12
X-rays
1018
Wavelength (m)
Gamma rays
1020
1022
Frequency (Hz)
• Diffraction – the bending of
waves at an aperture or obstacle
Double-slit pattern of water/sound
waves
• Interference – double-slit, speckle

Optic axis
Ipeak=4Io
screen
y

D

d
Path difference = d sin 
Iaverage=2Io
• Polarization
Light as a particle
•
•
•
•
Photon
Energy packet
Photoelectric effect
Double slit- revisited
photocathode
anode
A
*
*
*
Double Slit Experiment with Electrons
Detections come in lumps = quanta
Intensity exhibits interference
Reducing intensity of the
light, so that only one
electron arrives at the slits
at a time
Questions?
Why do no electrons (or photons)
ever arrive at some locations?
Clearly
Ptot ( x)  P1 ( x)  P2 ( x)
How can we get interference when
only 1 particle at a time is going
through the slits? What does that
particle interfere with?
Suppose we actually check which slit
each particle went through and know
with certainty – what happens then?
How can this be?
Resolution comes from QED with
Feynman
Electron diffraction
How is light produced?
• Chemical energy - fire
• Electrical energy - lightning
• Nuclear energy - stars
– Incandescent
– Electric discharge – continuous vs discrete
spectrum
– Fluorescence
Special Properties of Laser Light
•
•
•
•
•
Monochromatic
Intense
Pencil beam – collimated
Coherent
Can be cw or pulsed
Prototype Laser
•
•
•
•
•
•
Energy levels
Absorption, spontaneous emission
Stimulated emission
Population inversion
Metastable state
Pump – optical, electron excitation, atomatom collisions, chemical
• Resonant cavity – gain, cavity modes,
beam
Types of Lasers
• 3-level vs 4-level
• Ruby, first, a 3-level
pulsed laser
• He-Ne, gas, 4-level
• Argon ion, gas
• CO2 – molecular gas laser
• Neodymium – solid-state
Diode laser
Dye – liquid laser
Laser Applications
• Communications
• Coding information, fiber optics
• Medical uses
• Materials processing
• Science
Laser Tweezers
Pout
Pin
Pin
Pout
Pright
Pleft
Pnet
• Holography