Apparatus and method for reducing spatial coherence and for improving uniformity of a light beam emitted from a coherent light source
First Claim
1. A method for eliminating speckle structures formed by speckle spots in an illumination plane of an optical system having a coherent light source by reducing spatial coherence of illumination, comprising:
- providing at least one microlens array, which consists of a plurality of microlenses, in the optical path between said coherent light source and said illumination plane;
igniting said coherent light source for generating a light beam;
moving said at least one microlens array with the speed sufficient for introducing phase heterogeneity in the light wavefront for speckle elimination;
passing said light beam through said rotating microlens array;
and creating a speckle-free and uniform light distribution in said illumination plane, said coherent light source being a continuous laser which operates during an exposure time and wherein said rotation averages said speckle structures during said exposure time.
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Abstract
A method and apparatus for elimination of speckle pattern in optical system by reducing coherence. The invention is based on the use of a rotating microlens array having a rotational speed chosen with reference to laser parameter. For a continuous laser this relationship consists in that the exposure time is sufficient for overlapping at least 104 spot sizes of the speckle. For a pulse laser, the laser pulse time should be sufficient for shifting the speckle spot at least by the magnitude of its diameter. Several embodiments with modified coherence reduction units are available. One modified embodiment describes a rotating inclined plate which enhances coherence reduction by scanning the over the surface of the diffuser. Another embodiment describes the use of an optical conical rod with total internal reflection for creation of a plurality of non-coherent light sources.
309 Citations
21 Claims
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1. A method for eliminating speckle structures formed by speckle spots in an illumination plane of an optical system having a coherent light source by reducing spatial coherence of illumination, comprising:
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providing at least one microlens array, which consists of a plurality of microlenses, in the optical path between said coherent light source and said illumination plane; igniting said coherent light source for generating a light beam; moving said at least one microlens array with the speed sufficient for introducing phase heterogeneity in the light wavefront for speckle elimination; passing said light beam through said rotating microlens array; and creating a speckle-free and uniform light distribution in said illumination plane, said coherent light source being a continuous laser which operates during an exposure time and wherein said rotation averages said speckle structures during said exposure time. - View Dependent Claims (2, 3)
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4. An apparatus for eliminating speckle structures formed by speckle spots in optical system having a coherent light source by reducing spatial coherence of illumination, said apparatus comprising:
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an illumination plane illuminated by a light beam generated by said coherent light source; and at least a diffuser for randomizing the wavefront of said light beam and a moving microlens array consisting of a plurality of microlenses, said diffuser and said moving microlense array being arranged sequentially in the direction of the propagation of said wavefront between said coherent light source and said illumination plane, each of said microlenses creating an individual point secondary light source which emits a microbeam toward said illumination plane; a beam modifier which modifies the shape and size of said light beam and is located between said coherent light source and said diffuser; a shutter located between said coherent light source and said diffuser for periodically opening an access of said light beam to said optical system; a collector lens located between said diffuser and said moving microlens array for transforming said light beam from a diverging beam into a substantially parallel light beam; and a condenser which aligns said microbeams into a common illumination area with uniform light distribution. - View Dependent Claims (5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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Specification