Transcript Week1-ppt - Information Services and Technology

Trivia Question
Which “Big Bang Theory” character is an Optical
Physicist?
(a) Sheldon Cooper
(b) Leonard Hofstadter
(c) Howard Wolowitz
d
c
b
a
e
(d) Raj Koothrappali
(e) Amy Farrah Fowler
The grand overview of Optics/Photonics
Historical Development: Ray Optics → Wave Optics → EM Optics →
Quantum Optics.
• We will cover only CLASSICAL Optics in this course.
• EM Optics is the most general for optical phenomena which can be explained
classically. This uses Maxwell’s Equations from Physics 121.
• Wave optics is a SCALAR approximation of EM Optics. (No vector properties of E Field)
• Ray Optics is an approximation in which wavelength short (Diffraction ignored).
Why are we not covering book in order?
• Material will be covered in the ‘logical’
historical progression of Ray then Wave then
EM optics. Text book chapters are not ordered
in this ‘logical’ progression.
• Ray optics requires ALOT less math.
• EM optics requires the most. So let’s start easy
and make things harder (math wise) as we go.
The Electromagnetic Spectrum Chpt. 3.6
The Electromagnetic Spectrum
• Optics and Photonics is an enabling technology and science
• It enables advances in many different disciplines of science,
engineering, etc.
Radio Waves
• Power Transmission
• Radio Broadcasts
Radio Astronomy
http://www.ovsa.njit.edu/
Microwaves
Microwaves
Microwave source (Magnetron) melted a
candy bar in Spencer’s pocket. The next
day, he put an egg near the microwave
source. It cooked and exploded…..
The rest is history
Microwaves
Microwaves – Big Bang Discovery
Cosmic background Radiation – Residual ‘Big Bang’ radiation from thermal
‘black body’ spectrum corresponding to radiation at T=2.7K
Terahertz (THz)
• Non-destructive Evaluation
• Security Screening
• Wireless Communications
Concealed Threats in Packaging
TRANSMISSION
Plastic knife and metal razor
blade identified through
packaging
Concealed Threats in Clothing
REFLECTION
Knife in shirt pocket
Unmodified Explosive
simulant
•
•
•
•
Terahertz Wireless Communication:
Motivation
Demand for wireless data increasing
Size of Wireless Cells Shrinking
How can you provide high-bandwidth wireless
services (streaming video, 4K broadcasts,
communications among cars)?
Why are ‘unlimited’ data smart phone options no
longer available?
Graphics courtesy of AT&T Labs
Futuristic view of THz Communications:
Actively steered THz beams form ultrahigh capacity link to moving users.
The THz frequency range in USA is
unassigned above 300GHz.
15
Demand for Wireless Services
constantly increasing
S. Cherry, “Edholm’s law of bandwidth,” IEEE Spectr. 41, 50 Jul. 2004.
• According to Edholm’s law of bandwidth, the demand for bandwidth in wireless
short-range communications has doubled every 18 months over the last 25 years.
Examples….
Feb 2011, Cisco Visual Networking Index: Global
Mobile Data Traffic Forecast Update 2010-2015
Large increase in data traffic for MOBILE
Devices
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Commercial THz Wireless Systems
(in Demonstration)
NTT, 2012 Beijing Olympics
But in USA, commercial systems >100GHz can not be
sold… So little commercial development relative to
Europe and Asia
Japanese Government and Industry
(NTT) have committed to THz HD
wireless broadcasts for 2020 Tokyo
Olympics
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Infrared – Thermal Imaging
Infrared – Thermal Imaging
Vegetation Mapping
“Red Edge”
http://speclab.cr.usgs.gov
My research group is adapting
‘multispectral imaging’ to crime
scene investigations and ‘drones’.
Visible - Oximeter
Visible - Oximeter
UV-Sun/ Crab Nebula – Skin Cancer
X-rays
X-ray
X-ray
Postulates of Ray Optics
• Light travels as Rays
• Medium characterized by refractive index n
n
c0
c
OPL  Lo n
n 1
t
Lo n
co
• For inhomogeneous medium, the time taken for light
to travel from A to B is proportional to optical path
length
B
OPL   n(r) ds
A
OPL   ni Li
i
• Fermat’s Principle – Light rays travel along the path to
minimize the transit time.
Other things appear blue
due to scattering…..
Three general classes of Scattering
Depending on Particle size
Consider a column of MANY scattering
Centers….
Primary
wave
New Wavefront
(Secondary
Wave)
In forward direction, scattered light
forms a wavefront in the same direction
Interference (Brief)
Etotal  E1  E2
Waves which are IN PHASE will add together. Waves
which are OUT of phase, when added together will cancel
each other
New Wavefront
Even if scattering centers
NOT in an organized row,
forward going scattered
light forms a new
wavefront which transmits
through medium
What about lateral (side) scattering?
Destructive
interference
For a particular spacing
between scattering centers,
the scattered waves will
DESTRUCTIVELY interfere
and cancel each other
Since there are MANY scattering
centers (eg. number of atoms in a
solid), we can ALWAYS add the
scattering centers in pairs which
individually destructively interfere.
xo 
qe Eo
1
1/2
me  2
2 2
2 2
o       
  
  tan  2
2
 o   
1
Eo eit
xo e
i (t  )
Reflection from a boundary
Reflection from a boundary
Reflection from a boundary
Reflection from a boundary
Reflection from a boundary
Rays and Wavefronts
Rays are perpendicular to wavefronts: wavefronts denote surfaces of CONSTANT
phase
Specular Reflection
(from flat surface)
All in one plane
Diffusion Reflection
(from rough surface)
NOT all in one plane
Stealth fighter designed to avoid Diffuse
Reflection from radar waves. Reflected
waves directed so that reflected light does
not retrace path back to be detected.
Huygen’s Principle
• Break up wavefront into individual points which
each acting as a point source.
• Allow each spherical wavefront to propagate
according to the local speed of light in the
medium.
• Combination of spheres defines new wavefront.
New wavefront is the line or curve of the crests/
troughs of the point sources of waves
• Direction of travel (ray) is perpendicular to
wavefront
Refraction
Pencil appears to
be Bent at surface
of water
Object is DEEPER in
water than it appears.
Hint: use this figure
to visualize Problem
4.25.
Light refracts because speed of light and radius of
Huygen’s circle is different in the two mediums
v1
v2
Example of Fermat’s Principle Mirages
Cold Air more dense so
air travels SLOWER
Hot Air less dense so air
travels FASTER
Total Internal Reflection