1. Wave Optics The physics of interference, diffraction, thin films and more...

2. Reading in Text: Chapter 24 Main concept: light exhibits key properties that can only be explained by the wave model: –diffraction –interference –polarization

3. Wave Superposition and Interference What happens when waves meet? Path Difference - Phase Difference: illustrate this with the following appletapplet

4. Double and Multi-Slit Interfence Simple Case: Assume each slit acts as a single source a single source The Grating Equation for Antinodes: where d = separation between slits

5. Interfence Patterns Use the following applet to help explore the different interference patterns produced by single, double and multiple slits...applet

6. Single Slit Diffraction... A single slit can interfere with itself! simulate this simulate this Equation for Nodes:

7. General Equation for Single Slit Diffraction…Nodes Nodes will always form whenever

8. Poisson’s Spot - a curious tale! By the early 19th century the wave model was becoming accepted and the French Physicist Fresnel had worked out an elaborate mathematical theory of light. However, the famous physicist Poisson claimed to have found a fatal flaw in the theory...

9. The Physics of Thin Films A Phase difference can occur because of… –path differences for different combining wavetrains –phase shifts introduced under certain reflections –go to applet thin filmthin film

10. Path Differences to Phase Shifts... How to calculate phase shift: Find path difference Divide by wavelength of light IN THE FILM Add any additional phase shifts produced by reflections. If the phase shift is: –0.5, 1.5, 2.5, …. “n.5” then destructive interference will result –0,1,2,3,… n then constructive interference will result

11. Structural Colour in Plants and Animals The iridescent sheen of a bluebird wing or the extravagant colours of many butterflies and moths arise - not from chemistry (pigments) but from physics (interference effects)!!

12. The Physics of Structural Colour Light reflects from slightly different places along the surface. An optical path difference is introduced

13. Some colours work - some don’t... The optical path difference  is just the extra distance that one ray travels wrt to an adjacent one. It’s easy to see that this leads to: for constructive interference

14. Application… Lens Coating Why do some lens have a purple colour? Use the applet thin film to help understand the power of the “quarter wave”!thin film

15. Keeping Score (early 19th Century) Particle Model straight line propagation (1) reflection (1) refraction (1) dispersion (?) = 0.5 interference/diffraction (0) polarization (0) score = 3.5 Wave Model straight line propagation (1) reflection (1) refraction (1) dispersion (1) interference/diffraction (1) polarization (1) score = 6

16. So - if it’s a wave - What Kind of Wave? Known since antiquity - some crystals (calcite) can cause light to refract into two distinct paths when passing through the crystal (1669 - Bartholinus) Early 19th century, light under glacninc collisions can exhibit a “new property” - polarization Light is a transverse wave

17. Polarization, Scattering and The Electromagnetic Theory Why does glancing reflection from dielectric materials produce horizontally polarized light? Why is the sky blue? Why is skylight polarized? How are scattering and polarization linked? What is light? go to simulation go to simulation