<title>Comparison of 3D surfaces produced by 248-nm and 193-nm excimer laser radiation</title>

Abstract

Currently there is a strong demand for refractive optical elements made from glass in 21/2D and 3D-structures. Due to the characteristics of brittle materials like glass, only a limited number of manufacturing methods can be used to machine these materials with sub-micron resolution. Thus, current microstructures made out of glass are mainly manufactured by photolithography and etching process. Lithography techniques are only for economic purposes for a series production, but is not suitable for manufacturing prototypes or a small series. Micromachining done with Excimer Lasers in combination with high precision CNC- controlled handling systems offers flexible design possibilities for optical components. Due to the limitations of conventional machining techniques for brittle materials, a new laser machining system for material processing at a wavelength of 193 nm has been designed and built. The better absorption of 193 nm compared to 248 nm or larger wavelengths leads to damage free microstructuring of most glasses. Data generation for the volume to be ablated starts with the mathematical description of the surface shape of the optical component. The contour can be derived from a mathematical function or individual xyz-data point information from any CAD-program. A pre-processor calculates the CNC-data for laser triggering, xyz-table and the CNC- mask control. Each laser pulse leads to a material removal, defined by the illuminated surface on the workpiece as well as the energy density. Superposition or overlapping of pulses allows the creation of the desired surface. The surface roughness is determined by the wavelength as well as the chosen ablation strategy. To achieve best results, the process has to be carefully adjusted for a specific material. This technique is a sufficient method for structuring grooves in ceramics or glass as well as producing aspherical transparent optical surfaces or micro lens arrays. This paper shall describe the potential of 193 nm treatment of 3D micro surfaces with an optimized process machine and data handling system in comparison with results originating from 248 nm laser processing.