GIPHOTOSTOCK / SCIENCE PHOTO LIBRARY GIPHOTOSTOCK / SCIENCE PHOTO LIBRARY
Incoherent and coherent superposition. When two coherent waves of light are superimposed, the resulting intensity depends on the phases of both waves. Here a laser beam was spit into two beams that were then crossed at a small angle. Characteristic interference fringes were observed (bottom panel). For two incoherent waves, the total intensity is a sum of individual intensities. Here this was obtained by making a double exposure and blocking each beam one at a time (top panel).
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