1. PHYS 252 / 2021 PHYS 252 & PHYS 202 Polarization Scattering Absorption

2. PHYS 252 / 2022 Polarization The polarization of the light wave is determined by the oscillation axis of the electric field. polarization typedescription linearly polarizedaxis is in one direction elliptically polarizedaxis sweeps out ellipse over time circularly polarizedaxis sweeps out circle over time unpolarizedaxis changes direction randomly

3. PHYS 252 / 2023 Polarization crest trough linearly polarized

4. PHYS 252 / 2024 Polarization UnpolarizedLinearly Polarized

5. PHYS 252 / 2025 Polarization Linear Polarization of Light by Dichroic Polarizer (Polaroid) transmission axis E incident electric field The energy from this perpendicular component is absorbed. This component gets through.

6. PHYS 252 / 2026 Polarization Effect of a Single Polaroid on Linearly Polarized Light EEEE all light passes through less light passes through even less light passes through no light passes through

7. PHYS 252 / 2027 Polarization Two Polaroids I = I o cos 2  The Law of Malus

8. PHYS 252 / 2028 Polarization Linear Polarization of Light by Reflection polarization angle

9. PHYS 252 / 2029 Polarization Linear Polarization of Light by Reflection n 1 n 2  p air off water11.3353.1  air off glass11.556.3  Examples tan  p = n 2 / n 1 Polarization Angle All of the reflected light is linearly polarized parallel to the reflecting surface when the incident angle equals the polarization angle.

10. PHYS 252 / 20210 Polarization Birefringent Material Birefrigence material exhibits two values of refractive index for each frequency of light the value depends on the orientation of the electric field with the optic axis of the material Calcite optic axis

11. PHYS 252 / 20211 Polarization Linear Polarization of Light by Birefringent Crystal extraordinary ray ordinary ray

12. PHYS 252 / 20212 Polarization Rotation of Polarization Axis by Birefringent Material Amount of rotation depends on thickness of material wavelength of light values of refractive index

13. PHYS 252 / 20213 Scattering Atoms, molecules, and small particles scatter light by absorbing it and re-emitting it in random directions. Amount of scattering depends on size of scatterers wavelength of light

14. PHYS 252 / 20214 Scattering shorter wavelengths scatter much more than longer wavelengths Rayleigh Scattering size of scatterers is small compared to wavelength of light amount of scattered light Example: Scattering of sunlight by oxygen & nitrogen molecules in Earth’s atmosphere Daytime: sky looks blue, Sun looks yellow/white Sunrise/Sunset: Sun looks orange/red

15. PHYS 252 / 20215 Scattering sunset D ~ 820 km Rayleigh Scattering D ~ 50 km daytime 6380 km www.bigfoto.com/themes/nature/sky/

16. PHYS 252 / 20216 Scattering Linear Polarization by Scattering

17. PHYS 252 / 20217 Absorption Atoms and molecules will absorb light energy of certain frequencies (and wavelengths) much better than others. A plot of the amount of absorption versus frequency (or wavelength) is called a material’s absorption spectrum. Some example absorption spectra appear on the next slides.

18. PHYS 252 / 20218 Absorption Absorption Spectra of Some Organic Materials 1.bacteriochlorophyll 2.chlorophyll A 3.chlorophyll B 4.phycoerythroblin 5.beta carotene A careful look at the chlorophyll spectra will explain why most plants are green!

19. PHYS 252 / 20219 Absorption What color is this material? Absorption spectrum of red garnet.