trivia question which “big bang theory” character is an optical physicist? (a) sheldon cooper...

Trivia Question

Which “Big Bang Theory” character is an Optical Physicist?(a) Sheldon Cooper(b) Leonard Hofstadter(c) Howard Wolowitz(d) Raj Koothrappali(e) Amy Farrah Fowler

d c a e b

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

http://www.ovsa.njit.edu/

Radio Astronomy

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 DiscoveryCosmic 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

Plastic knife and metal razor blade identified through packaging

TRANSMISSION

Concealed Threats in Clothing

Knife in shirt pocket Explosive simulant

REFLECTION

Unmodified

Terahertz Wireless Communication: Motivation

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Outline:• Demand for wireless data increasing• Size of Wireless Cells Shrinking• Examples of THz systems• NSF Expeditions Application : 100Gb/s Data Centers

Futuristic view of THz Communications: Actively steered THz beams form ultra-

high capacity link to moving users.

Graphics courtesy of AT&T Labs

The THz frequency range in USA is unassigned above 300GHz.

Demand for Wireless Services constantly increasing

16

• 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.

S. Cherry, “Edholm’s law of bandwidth,” IEEE Spectr. 41, 50 Jul. 2004.

Examples….

Feb 2011, Cisco Visual Networking Index: Global Mobile Data Traffic Forecast Update 2010-2015

Large increase in data traffic for MOBILE Devices

Commercial THz Wireless Systems (in Demonstration)

17

But in USA, commercial systems >100GHz can not be sold… So little commercial development relative to Europe and Asia

NTT, 2012 Beijing Olympics

Japanese Government and Industry (NTT) have committed to THz HD wireless broadcasts for 2016 Tokyo Olympics

Infrared – Thermal Imaging

Infrared – Thermal Imaging

http://speclab.cr.usgs.gov

Vegetation Mapping

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

• For inhomogeneous medium, the time taken for light to travel from A to B is proportional to optical path length

• Fermat’s Principle – Light rays travel along the path to minimize the transit time.

0cnc

1n oOPL L n o

o

L nt

c

(r) dsB

A

OPL n

i ii

OPL n L

Other things appear blue due to scattering…..

Three general classes of Scattering Depending on Particle size

Interference (Brief)

1 2totalE E E Waves which are IN PHASE will add together. Waves which are OUT of phase, when added together will cancel each other

Consider a column of MANY scatteringCenters….

New Wavefront

In forward direction, scattered light forms a wavefront in the same direction

(Secondary Wave)

Primary wave

New WavefrontEven 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?

For a particular spacing between scattering centers, the scattered waves will DESTRUCTIVELY interfere and cancel each other

Destructive interference

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.

1/222 2 2 2

1e oo

eo

q Ex

m

12 2

tano

i toE e

( )i tox e

Reflection from a boundary

Reflection from a boundary

Reflection from a boundary

Reflection from a boundary

Reflection from a boundary

Rays and WavefrontsRays are perpendicular to wavefronts: wavefronts denote surfaces of CONSTANT phase

Specular Reflection (from flat surface) Diffusion Reflection

(from rough surface)

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

RefractionPencil 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

1v

2v

Example of Fermat’s Principle - Mirages

Hot Air less dense so air travels FASTER

Cold Air more dense so air travels SLOWER

Total Internal Reflection