Freeform microlens array homogenizer for excimer laser beam shaping

Abstract

We presented a novel technique to design microlens optical beam homogenizing system for excimer lasers. As a new approach by applying freeform surface microlens array, the homogenizer can yield somehow superior beam shaping results with larger but less microlens units than conventional method. With new concept and design, the diffraction effects at the microlens apertures can be reduced substantially. Large scale and highly uniform beam profile can be realized at a relative nearby working distance after beam shaping. This is hard to achieve by conventional method. Our design method takes the real spatial energy characteristics of the excimer laser beam as the design basis, and combined with feasible optimization method. The design method is demonstrated as a real instance based, on a 193 nm ArF excimer laser in our laboratory. Moreover, to verify the effectiveness of our method, the designed freeform microlens array homogenizer has been fabricated and tested experimentally. The experimental optical performance of the homogenizer coincides well with the theoretical simulation.