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Electro-Optical Instrumentation: Sensing and Measuring with Lasers by Silvano Donati - University of Pavia

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Chapter 5Speckle-Pattern Instruments

When light from a laser source is shed on a plain surface like a sheet of paper or a white wall, the spot appears granular (Fig.5-1). This appearance is termed speckle pattern and came as a surprise to the first researchers experimenting with lasers.

Indeed, spatial coherence was a predicted feature of the laser beam, and common sense was that a laser spot should look smooth. Actually, the spatial distribution of a mode is smooth, and as such is preserved when the beam impinges on a smooth surface. However, a smooth surface is one with roughness much smaller than wavelength, and only a mirror satisfies this condition.

In a normal diffuser or diffusing surface, one with a brightness that looks the same from ...

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