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F.3.70 Diffraction from a CD and a DVD

Concept: Laser light is reflected from a CD and a DVD. The differences between the two diffraction patterns are observed.
Keywords: light wave, wave length, grating spacing, fringes, order number, diffraction, interference, diffraction condition

Time to setup: 10 min
Time to demo: 5 min

Equipment list, location(s)
Green laser, CD, DVD.

Notes and suggestions to instructor
Questions: What are the differences between the patterns produced by a CD and a DVD? What are the line spacings on a CD and a DVD? (1.6 micron and 0.74 micron respectively.) From certain DVDs the fringes in the diffraction pattern are doubled. Why? (Because longer DVDs have two layers, one reflective and one semi-reflective separated by a distance of 0.6 mm from each other.)

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