Variable xy-UV beam expander for high-power laser beam shaping

Abstract

A five element zoomable anamorphic beam expander is designed and fabricated for a laser illumination system used in the manufacture of patterned micro-circuit substrates. The beam expander is the front end of a Gaussian to top-hat beam shaping illuminator. The tightly toleranced optical system downstream of the beam expander should not be readjusted with changes to the input beam. The job of the beam expander is to maintain, independent of the input beam, a constant diffraction limited output beam size as well as a specific waist location. A high power quasi-CW laser at 355 nm is employed for high throughput. The specifications of the laser allow for a range of x,y-beam diameters (ellipticity), x,y-waist locations (astigmatism), and x,y-divergence. As the laser’s frequency tripling crystal is exposed to high fluence over time, the beam parameters will change. At some point the laser is exchanged for a new one, and a new set of beam parameters is presented to the beam expander. Movable cylindrical lenses enable the independent adjustment of x- and y-beam parameters. The mounting cells are motorized to enable adjustments remotely. We present the optical design approach using Gaussian beam ray tracing and discuss the mechanical implementation.