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Lec20 - LECTURE 20 Interference Diffraction Resolution...

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1 LECTURE 20: Interference, Diffraction, Resolution http://antwrp.gsfc.nasa.gov/apod/image/0507/47tuc_chandra_f.jpg 11/7/10 2 Interference *Three ways in which the phase difference between two waves can change: 1. By traveling though media of different indexes of refraction 2. By traveling along paths of different lengths 3. By reflection from a boundary A wave will undergo a 0.5 wavelength phase shift if it reflects off a medium with higher index of refraction 11/7/10 3 Interference: Double Slit (for very narrow slits) *The phase difference between two waves can change if the waves travel paths of different lengths. Interference maxima for d sin θ m = m λ , m = 0,1,2,... Interference minima for d sin θ m = m + 1 2 λ , m = 0,1,2,... Flaring of light 11/7/10 4 Interference: Double Slit ( DEMO ) two slits Laser ( L ight A mplification by S timulated E mission of R adiation) He, Ne laser Interference patterns visible on screen (Coherent light source)
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2 11/7/10 5 Diffraction * When a wave encounters an edge, obstacle, or aperture with a size comparable to its wavelength λ ( d ≈λ ) , those waves spread out. This effect is called diffraction. This regime is called wave optics (geometrical optics is no longer a good approximation).
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