spatial filter

Definition: (1) Pinhole used to produce a clean laser beam for e.g. holography: a precision laser-cut hole in a metal plate is placed at the rear focal plane of a laser beam expander (usually a microscope objective). * The hole lets through only the central, most coherent, core of the laser beam. (2) Mask e.g. a clear ring in an opaque plate designed to separate a desired part of a coherent light-beam.

Related Terms: speckle pattern

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