Patent Number: 6,252,714

Title: Diffractive homogenizer with compensation for spatial coherence

Abstract: A diffractive homogenizer is provided for receiving a beam of laser energy and producing a desired illumination pattern in a target plane. The homogenizer is made up of a plurality of diffractive sub-elements, each of which contributes to all or a portion of the desired image. By combining the contributions of many sub-elements to form the final image, a homogenizing effect is realized. In preferred embodiments, the sub-elements are designed to compensate for the finite spatial coherence of the incident laser beam and to control the numerical aperture distribution of the transmitted light. Each sub-element is composed of a large number of discrete pixels, each of which alters the phase of radiation passing therethrough by a selected amount. The pixel arrangement is chosen, using computer modeling and optimization techniques, such that the interference pattern created by the collective pixels in a sub-element makes up the desired image (or a portion thereof). A technique is also provided for reducing the intensity of the image formed by a selected sub-element, which may be located in a laser "hot spot", by randomizing a selected percentage of the pixels located in that sub-element. This diffractive homogenizer is useful in various laser ablation and annealing, and other laser material processing applications.

Inventors: Guenther; Reid L. (Austin, TX), Shoemaker; Curtis L. (Round Rock, TX)

Assignee: 3M Innovative Properties Company

International Classification: G02B 27/09 (20060101); G02B 5/32 (20060101); G02B 027/46 ()

Expiration Date: 06/26/2018