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Abstract

A laser system which utilizes a reflective objective lens includes a closed loop servo and beam profiling system to provide improved uniformity of the laser beam impinging on the work piece. The laser beam is passed through an aperture to pattern the work piece. A beamsplitter separates the laser beam into workpiece and diagnostic beams. The workpiece and diagnostic beams are both passed through identical reflective objective lenses, to accurately measures performance of the work piece beam. Preferably, a third reflective objective lens collimates the diagnostic beam and directs it to a beam analyzer where the uniformity can be accurately assessed. The information determined by the beam analyzer is then used to position a pre-aperture converging optic (PACO) located between the laser source and the aperture. Adjustments in the x- and y-dimensions of the PACO lens change the angular uniformity at the aperture. Adjustments in the z-dimension of the PACO lens adjust the energy density delivered to the work piece. Homogenizing the laser light provides increased spatial uniformity. In one technique, a fiber optic bundle randomly redistributes the gaussian input energy to achieve spatial uniformity. Preferably, the output end of the fiber optic bundle is annular in shape, while the input end is rectangular to effectively capture light output from a laser, and prevents or reduces energy losses. In another technique, a fine mesh screen or combination of screens is inserted into the path of the laser beam prior to the aperture. The screen or combination of screens is positioned with respected to the converging lens and aperture or mask such that both spatial and angular uniformity result at the mask or aperture planed, and, hence, the work plane.

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