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OPTI 201R L2

# OPTI 201R L2 - 1.3 W a v e f r on t s a n d R a y s 19"A...

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OPTI 201R Fall 2009 19 1 . 3 Wav e front s and Ray s : "A wav e fron t is, therefore, a set of points with equal phase located at regular intervals from the source of light." (pg.9) ► These intervals are equal to the wavelength of the EM wave. "The optical path length relative to the source is constant over the wavefront." (pg.9) ► Consider a tiny (point) source of light, radiating uniformly (isotropically) into a sphere: Fig. 1.6 - The wavefronts from a point source are spherical . (drawing shows these 3-D spherical shells as 2-D circles) - As the EM wave travels, the radius of any given wavefront increases (at the speed of the wave). - At an infinite distance, the radii become infinite, and the wavefronts are flat (planar). At infinity, the spherical waves have turned into plane waves .

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OPTI 201R Fall 2009 20 "A ray is the vector representation of an EM wave, pointing in the direction of propagation." ► A ray is, therefore, a path followed by the wavefront. ► A ray is perpendicular to the wavefront.
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OPTI 201R L2 - 1.3 W a v e f r on t s a n d R a y s 19"A...

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