1. 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

2. 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).

3. 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.

4. The Electromagnetic Spectrum Chpt. 3.6

5. The Electromagnetic Spectrum
Optics and Photonics is an enabling technology and science
It enables advances in many different disciplines of science, engineering, etc.

6. Radio Waves
Power Transmission
Radio Broadcasts

7. Radio Astronomy

8. Microwaves

9. 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

10. Microwaves

11. Microwaves – Big Bang Discovery
Cosmic background Radiation – Residual ‘Big Bang’ radiation from thermal ‘black body’ spectrum corresponding to radiation at T=2.7K

12. Terahertz (THz) Non-destructive Evaluation Security Screening
Wireless Communications

13. Concealed Threats in Packaging
TRANSMISSION
Plastic knife and metal razor blade identified through packaging

14. Concealed Threats in Clothing
REFLECTION
Knife in shirt pocket
Unmodified
Explosive simulant

15. Terahertz Wireless Communication: Motivation
Outline:
Demand for wireless data increasing
Size of Wireless Cells Shrinking
Examples of THz systems
NSF Expeditions Application : 100Gb/s Data Centers
Graphics courtesy of AT&T Labs
Futuristic view of THz Communications: Actively steered THz beams form ultra-high capacity link to moving users.
The THz frequency range in USA is unassigned above 300GHz.

16. Demand for Wireless Services constantly increasing
S. Cherry, “Edholm’s law of bandwidth,” IEEE Spectr. 41, 50 Jul
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
Large increase in data traffic for MOBILE Devices

17. Commercial THz Wireless Systems (in Demonstration)
Japanese Government and Industry (NTT) have committed to THz HD wireless broadcasts for 2016 Tokyo Olympics
NTT, 2012 Beijing Olympics
But in USA, commercial systems >100GHz can not be sold… So little commercial development relative to Europe and Asia

18. Infrared – Thermal Imaging

19. Infrared – Thermal Imaging

20. Vegetation Mapping

22. Visible - Oximeter

23. Visible - Oximeter

24. UV-Sun/ Crab Nebula – Skin Cancer

25. X-rays

26. X-ray

27. X-ray

28. 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.

29. Other things appear blue due to scattering…..

30. Three general classes of Scattering Depending on Particle size

31. Interference (Brief)
Waves which are IN PHASE will add together. Waves which are OUT of phase, when added together will cancel each other

32. Consider a column of MANY scattering
Centers….
Primary wave
(Secondary Wave)
In forward direction, scattered light forms a wavefront in the same direction

33. Even if scattering centers NOT in an organized row, forward going scattered light forms a new wavefront which transmits through medium

34. 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.

37. Reflection from a boundary

38. Reflection from a boundary

39. Reflection from a boundary

40. Reflection from a boundary

41. Reflection from a boundary

42. Rays and Wavefronts
Rays are perpendicular to wavefronts: wavefronts denote surfaces of CONSTANT phase

43. 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.

44. 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

45. 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.

46. Light refracts because speed of light and radius of Huygen’s circle is different in the two mediums

47. Example of Fermat’s Principle - Mirages
Cold Air more dense so air travels SLOWER
Hot Air less dense so air travels FASTER

48. Total Internal Reflection