Advanced high-resolution cylinder structuring with parallel Bessel beams under use of UV femtosecond laser radiation

Abstract

The requirements on the resolution of direct laser structuring are constantly growing and are now firmly in the sub-μm range. However, strong focusing of a Gaussian beam near diffraction limit is accompanied by a very limited depth of focus, which leads to an extreme increase in process sensitivity. To overcome the problem of the short focal tolerance, nondiffracting Bessel beams can be applied providing a depth of field in the mm range while allowing the diameter of the central processing spot to be 1 μm. Features in this size range are needed, for instance, for printed electronics such as highresolution displays. Since the reduction of the focus diameter is coupled with a decrease in productivity, the process must be parallelized to set the foundation for the industrial exploitation of Bessel beam technology for the manufacture of embossing and printing tools. This contribution presents the optical setup of a laser structuring machine that works with four parallel Bessel beams. Each beamlet can be modulated individually to enable the flexible generation of arbitrary surface structures. Ablation results with structure sizes of 1 μm are presented. A strategy to estimate the position-dependent peak fluence has been developed based on CMOS images of the Bessel beam along the propagation. This knowledge about the fluence is particularly relevant to prevent ablation by side lobes and to transfer the experience from ultrafast laser ablation with conventional Gaussian beams to the Bessel beam processing. Furthermore, this paper presents a novel approach to lateral Bessel beam scanning for efficient machining of cylinders based on RF shifting in AOMs or AODs.