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Abstract

Optical elements with small increments in average density are formed in a substrate by laser micromachining using a variable aperture and a pattern mask set of pattern masks each having of shape-defining elements whose density differs among the pattern masks in first density increments. A laser light beam passes through a combined mask formed by the variable aperture and one pattern mask selected from the pattern mask set. The variable aperture controls beam size and the pattern mask spatially modulates its intensity. A focusing element focuses light from the combined mask on a small averaging region of the substrate. Different combinations of the size of the aperture mask and the selected pattern mask are used in combination at respective averaging regions of the substrate. The resulting average densities of the optical elements vary among the averaging regions in increments that are small compared to the first density increments.

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