Optics and Photonics

1. Optics and Photonics Dr. Kevin Hewitt Office: Dunn 240, 494-2315 Lab: Dunn B31, 494-2679 Kevin.Hewitt@Dal.ca Friday Sept. 6, 2002

2. Course Information • Optics is light at work • Textbook: Optics (4th edition), Eugene Hecht, $152.39 • Reference: Introduction to Optics, F. & L. Pedrotti, • Description: Two areas will be covered: • Geometrical optics:  < dimension of aperture/object • Wave (i.e. physical) optics: > dimension of aperture/object • Selected topics: • What are your areas of interest? • Lasers, holography, fiber optic communication, functions of the eye… • Pre-requisites: PHYC 2010/2510 and MATH 2002

3. Course Information • Grading: • Problem sets 20% • Midterm 20% • Oral Presentation 20% • Final exam 40% • Problem sets: • 1 per week • Hand-out/Hand-in every Wednesday (begin Sept. 11)

4. Class Schedule

5. Class Schedule

6. Key Dates

7. Optics Nature of Light (Hecht 3.6)

8. Nature of Light • Particle • Isaac Newton (1642-1727) • Optics • Wave • Huygens (1629-1695) • Treatise on Light (1678) • Wave-Particle Duality • De Broglie (1924)

9. Young, Fraunhofer and Fresnel(1800s) • Light as waves! • Interference • Thomas Young’s (1773-1829) double slit experiment • see http://members.tripod.com/~vsg/interf.htm • Diffraction • Fraunhofer (far-field diffraction) • Augustin Fresnel (1788-1827) (near-field diffraction & polarization) • Electromagnetic waves • Maxwell (1831-1879)

10. Max Planck’s Blackbody Radiation (1900) • Light as particles • Blackbody – absorbs all wavelengths and conversely emits all wavelengths • The observed spectral distribution of radiation from a perfect blackbody did not fit classical theory (Rayleigh-Jeans law)  ultraviolet catastrophe

11. M = T Rayleigh-Jeans law Cosmic black body background radiation, T = 3K.

12. Planck’s hypothesis (1900) • To explain this spectra, Planck assumed light emitted/absorbed in discrete units of energy (quanta), E = n hf • Thus the light emitted by the blackbody is,

13. Light of frequency ƒ Kinetic energy = hƒ - Ф Electrons Material with work function Ф Photoelectric Effect (1905) • Light as particles • Einstein’s (1879-1955) explanation • light as particles = photons

14. Luis de Broglie’s hypothesis (1924) • Wave and particle picture • Postulated that all particles have associated with them a wavelength, • For any particle with rest mass mo, treated relativistically,

15. Photons and de Broglie • For photons mo = 0 • E = pc • Since also E = hf • But the relation c = ƒ is just what we expect for a harmonic wave

16. Wave-particle duality • All phenomena can be explained using either the wave or particle picture • Usually, one or the other is most convenient • In OPTICS we will use the wave picture predominantly

17. Rays – lines perpendicular to wave fronts  Wave front - Surface of constant phase Propagation of light: Huygens’ Principle (Hecht 4.4.2) • E.g. a point source (stone dropped in water) • Light is emitted in all directions – series of crests and troughs

18. x Terminology • Spherical waves – wave fronts are spherical • Plane waves – wave fronts are planes • Rays – lines perpendicular to wave fronts in the direction of propagation Planes parallel to y-z plane

19. Huygen’s principle • Every point on a wave front is a source of secondary wavelets. • i.e. particles in a medium excited by electric field (E) re-radiate in all directions • i.e. in vacuum, E, B fields associated with wave act as sources of additional fields

20. New wavefront r = c Δt ≈ λ Given wave-front at t Allow wavelets to evolve for time Δt Huygens’ wave front construction Construct the wave front tangent to the wavelets What about –r direction? See Bruno Rossi Optics. Reading, Mass: Addison-Wesley Publishing Company, 1957, Ch. 1,2for mathematical explanation

21. Plane wave propagation • New wave front is still a plane as long as dimensions of wave front are >> λ • If not, edge effects become important • Note: no such thing as a perfect plane wave, or collimated beam