class22 - Announcements Reading for Friday 6.1 6.3 Exam 2...

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Announcements : Reading for Friday: 6.1 – 6.3 Exam 2 is next week (Tue. March 9 th , 7:30- 9:15pm). Topics: TZD, Chapters 1-5, 11.9, 11.10 Office hours: Today 1 – 3pm Today: LASERs! What’s so special about LASER light? A) It doesn't diffract when it goes through two slits. B) It can be collimated very well. C) The photons in the laser beam travel a little bit Q1 faster because they all go the same direction. D) Laser light is pure quantum light, and therefore, cannot be described with classical EM theory. E) Laser light is purely classical light, and therefore, it is incompatible with the photon picture. What’s so special about LASER light? Remember the word 'coherence'? (We used it occasionally in context with interferometers, diffraction and with photons.) There are two types of coherence: - Spatial coherence - Temporal coherence LASERs produce light with excellent spatial and temporal coherence. Spatial coherence Flashlight (incoherent) Collimating lens Laserpointer (coherent) Temporal coherence Flashlight (incoherent) c τ 'Mach-Zehnder' interferometer Laser (coherent) c · 1 c · 2 For very stable lasers: ( 1 - 2 ) max ~ 1 second. (This corresponds to 300’000 km path difference!)
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LASER Remember this one (from class 3) : E E-field (for a single color): E(x,t) = A 0 sin( ω t+ (x · ω ) / c + φ ) λ ω = 2 π f x A 0 Temporal coherence: ω and are very well defined constants (i.e. time independent). Let's make a coherent light pulp! Bad: Throw away most of the light and individual photons still have random phases Remember: Coherent light requires that ω and are constants. Color filter (passes only certain colors, ω ) Aperture How can we make identical photons?
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This note was uploaded on 08/24/2010 for the course PHYS 2130 taught by Professor Staff during the Spring '08 term at Colorado.

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class22 - Announcements Reading for Friday 6.1 6.3 Exam 2...

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