DOC PREVIEW
CU-Boulder PHYS 1230 - Scattering and Polarization

This preview shows page 1-2-3-4-5-6 out of 17 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 17 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 17 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 17 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 17 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 17 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 17 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 17 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

11Lec. 25, Tuesday, April 13Chapter 13: Scattering and PolarizationHomework is due in room G2B90 “in boxes”• Scattering:– Smoke, haze, fog, clouds, air, water, – Depends on wavelength, size of particle• Polarization:caused by reflection, scattering• Applications– Sunglasses– Photographic filters– LCD displays 1We are here1Thursday: Chapter 14, Holography. Next week: Chap. 8, Binocular visionExtra stuff: digital images2Small particles scatter lightParticles smaller than a wavelength of light scatter blue more than they scatter other colors. This is called Rayleigh scattering. Examples of small particles (smaller than λ): Air molecules (blue sky)Water molecules (blue ocean)Some smoke particles (slightly blue)Particle in the iris of your eye (blue eyes)3Not-so-small particles scatter lightParticles larger than a wavelength of light scatter all colors about the same. Examples of colorless particles which are larger than a wavelength of light:Rain cloudsDense smokeSmog Fat particles in milkBigger particles will reflect the color of the particleDenver brown cloud (road grit, sand) 4Red sunsets and blue sky are related? The red sunset is because the blue is scattered out, leaving behind white minus blue.5Some thought questions1. Why isn’t a glass of water blue?2. Why isn’t the air in the room blue?3. Why is the sun redder at sunset than at noon?4. Why do some cars have yellow fog lights?66Lec. 25, Tuesday, April 13Chapter 13: Scattering and Polarization• Scattering:– Smoke, haze, fog, clouds, air, water, – Depends on wavelength, size of particle• Polarization:caused by reflection, scattering• Applications– Sunglasses– Photographic filters– LCD displays 6We are here6Extra stuff: digital images7Polarization1. Polarized light has one direction for the electric force of the electromagnetic wave. 2. Polarizing filters pass one direction of polarization. Light can have a polarization between vertical and horizontal, and in this case a fraction gets through a polarizing filter: This much is horizontal polarization.This much isverticalpolarization.8Polarizing filters8Demo with grill9Two crossed polarizers block all light910Reflection from a smooth surface is polarized“Smooth” means glossy like metal, plastic, still water, not rough like paper or wood. Reflected light has the electric force (or electric field) parallel to the surface. 10Demo reflection from textbook11Reflection from a vertical wall or window?• Is the electric field of the reflected light vertical or horizontal?1112Polarization by scattering (1)The electric field of scattered light is perpendicular to the plane with the light source, you and the scatterer.12☺☺Electric field E is vertical13Polarization by scattering (2)The electric field of scattered light is perpendicular to the plane with the light source, you and the scatterer.13☺E is horizontal14Brewster’s angle is a cheap polarizer• Light reflected (from glass or water for example) at this particular angle is 100% polarized. 14This polarization is perpendicular to this pageThis polarization is parallel. θFor glass, Brewster’s angle is 56 degrees from the normal to the surface.15Natural birefringence• A birefringent material has two indices of refraction. One each polarization (measured relative to a crystal axis.)• Vertical and horizontal polarization are bent differently. 15Demo: calcite crystal and the word calcite on a viewgraph16Stress birefringenceClear substances that are stressed (bent, for example) will have birefringence that creates stress patterns when viewed through crossed polarizers.16Demo: stressed plastic or google image1717Lec. 25, Tuesday, April 13Chapter 13: Scattering and Polarization• Scattering:– Smoke, haze, fog, clouds, air, water, – Depends on wavelength, size of particle• Polarization:caused by reflection, scattering• Applications– Sunglasses– Photographic filters– LCD displays 17We are here17Extra stuff: digital images18Applications (1)Sunglasses: Filter is oriented to block horizontal polarization. Why?1819Applications (2)Photographic filter:Can be rotated for best looking picture. 1. Enhance reflection in lake. 2. Reject reflection in lake (see the fish). 3. Darken sky, enhance clouds. 4. Block light from haze.1920Surface reflection is blocked.21E is vertical because the sun is at the left. Notice the shadows. 222324Applications (3) : Liquid crystal displayExamples of liquid crystal displays (LCDs)Black and white displaysDigital watchesSome calculators Color displaysLaptop computer screensSome digital projectors for classrooms 24Textbook Ch. 13.7Source of light is reflection of room light.25How does an LCD panel work (1)25Battery disconnectedLight is passedLight emitting panelPolarizer PolarizerLiquid crystalsWith no voltage, liquid crystals rotate polarization 90 degrees, light is passed through crossed polarizers.26How does an LCD panel work (2)26Battery connectedLight is blockedLight emitting panelPolarizer PolarizerLiquid crystalsWith voltage, polarization is not rotated, light is blocked by the crossed polarizers.27What are liquid crystals?They are a liquid. The molecules can line up, like the atoms in a crystal. The lined up molecules can rotate the polarization. Apply a voltage to liquid crystals with electrodes on either side, and they line up differently. An array of wires (in rows and columns) goes to the pixels and voltages tell which one to be “on” or “off” or in-between. Color displays: have rows of red, green and blue filters over the pixels. 2728WikipediaLiquid crystals are not colored.Direction of light29Extra stuff: What is a digital image?First: What is a matrix?The matrix M is rows and columns of numbers. M1,1M1,2M1,3M2,1M2,2M2,3M3,1M3,2M3,32930Dot matrix printer30The numbers in the matrix are 0 for OFF and 1 for ON. The 0 or 1 is a bit. The matrix is a bit map. One dot is a pixel.31Why do I want more pixels?311. To make an enlargement2. To read the fine print32How many pixels does my display have?640 x 480 VGA used in 14 in. displays800 x 600 SVGA1024 x 768 XGA1280 x 1024 SXGA1600 x 1200 UXGA used in 20 inch displaysPixels in digital cameras: 2240 x 1680 (4 megapixels) 4064 x 2704 (11 megapixels) In color images, there are 3 subpixels, one for each color.32Two designs for color pixels. Wikipedia33How many shades of gray?Instead of 0 for black and 1 for white: 0 to 255 for shades of gray (256 values) 3334How many possible colors on your


View Full Document

CU-Boulder PHYS 1230 - Scattering and Polarization

Download Scattering and Polarization
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Scattering and Polarization and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Scattering and Polarization 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?