Grayscale homogenizers in calcium fluoride

Standard UV materials, such as ArF-grade fused silica, have impurities that lead to low transmittance, high absorption, and fluorescence when exposed to high irradiance. Calcium fluoride (CaF2), on the other hand, is a promising material for use as an optical diffuser for applications at 157nm, 193nm, and 248nm due to its low defect density and high transmission in the deep UV regime. In this paper, we discuss our method for fabricating Gaussian homogenizers in calcium fluoride using a grayscale photolithography process. Refractive microlens array homogenizers and Gaussian homogenizers have been fabricated in CaF2 and tested at 193nm for efficiency and uniformity. Using an excimer laser, uniformity results were obtained for cylindrical lens arrays in tandem and crossed to observe the homogeneity in an imaging configuration and for producing a square output. Efficiency, uniformity, and zero order measurements are provided for the Gaussian homogenizers.