Laser Basics and Applications Discussion

2. Announcements 11/19/12 • Prayer • Quick demo: diffraction from a hair • Lab 10 due tomorrow • Exam 3 starts Monday after break, goes through Saturday • Exam 3 review session: Monday after break, 4:30-6 pm, this room • Final exam: in Testing Center, M-Th week of finals Frank & Ernest

3. From warmup Extra time on? It would be nice to talk about the last parts of Chapter 10, it was hard to understand his explanation of the [wave]plates because it was a lot at once. Other comments? Is there any simple way to describe the quantum mechanics of lasers??? I want to know how they work.

4. From warmup • Which of the following is NOT true of the 3D “wave vector”? • Its magnitude is equal to 2π/λ. • For every point inside a plane wave, it points the same direction. • For every point inside a spherical wave, it points the same direction. • It tells us which way the wave is going. • In 1D it reduces to the wave number k.

5. Waves in 3-dimensions • Plane waves • polarization • Wave vector • direction of wave • Spherical waves General Form Specific Example

6. Student-designed problem: Transverse Wave • What direction do you want the wave to be traveling in? • What direction do you want the wave to be oscillating in? • What wavelength do you want the wave to have? • What do you want the wave’s amplitude to be? • What frequency (or velocity) do you want the wave to have? • What do you want the overall phase of the wave to be?

7. Clicker question • How many lasers do you have in your house/apartment? • 0 • 1 • 2 • 3 • 4+

8. From warmup • Name one cool thing about lasers that you didn't know prior to this reading assignment. • Lasers can help cool down temperatures to less than one millionth of a degree above absolute zero. (5 students) • The number which shocked me the most was the specificity of wavelength – that 99.99999999 percent of all light would be filtered away. (4 students) • It works by quantum mechanics. (3 students) • they can be focused more than regular light which make them useful for things like surgery or welding (2 students) • I didn't know that some of the qualities of lasers cannot possibly be mimicked by conventional light bulbs. -"higher order coherences“ ( 2 students) • Lasers are coherent sources of light. • Laboratory lasers produce light with wavelength variations of only 10^-6 nm • They are extremely efficient in regards to energy use. • they are used to read and write CD's • It was really cool learning more how they are made… • I watched Megamind on Friday, and wondered why Titan's laser eyes were melting and burnign the city away. Now I know why and he must have had powerful eyes.

9. Lasers Actual laser spectrum is over 100 narrower than the width of the red line • What makes a laser special? • Single wavelength • Intense • Collimated • Coherence (spatial, temporal) Laser spectrum Blackbody spectrum

10. Lasers Image & list from Wikipedia • Principal components: 1. Gain medium 2. Laser pumping energy 3. High reflector 4. Output coupler 5. Laser beam Stimulated Emission Absorption Emission Energy (light) Energy (light, electrical, etc.) light

11. Green laser pointer More Wikipedia 5. laser beam 1. gain medium (Nd:YVO4 crystal) 3. high reflector 4. output coupler 2. laser pumping energy (808 nm LED beam)

12. More Wikipedia

13. Circular Polarization Remember these pictures? Blue & green both represent electric fields. Ex out of phase with Ey. Pictures from Wikipedia

14. Optical Retarders, aka “Wave plates” • Quartz, SiO2: no = 1.544, ne = 1.553 • Calcite, CaCO3: no = 1.658, ne = 1.486 Calcite crystal: Pictures from Wikipedia

15. Optical Modulators Electro-optic modulator Acousto-optic modulator AOM EOM Field changes vertical index of refraction www.newport.com wikipedia