Combination of a micro-lens multi-spot generator with a galvanometer scanner for flexible parallel micromachining of silicon

Abstract

Multi focus optics are used for parallelizing production and for large-scale material processing. These elements split the beam into a periodic spot pattern with a defined grid and spot size. The challenge lies in the generation of a homogeneous envelope. Additionally the demand for flexible systems for an in-process changing of optical properties increases. Different components for multi spot generation like diffractive optical elements or micro lens arrays have been investigated. Diffractive optical elements offer large degree of freedom in the generation of arbitrary intensity distributions. In the paper we demonstrate the use of a diffractive element in combination with a multi spot generator.Within the paper we present the investigation of a micro lens array in a fly's eye condenser setup for the generation of homogeneous spot patterns. The multi spot generator is combined with a galvanometer scanner for forming an arbitrary shaped laser beam into a spot-, ring or arbitrary array pattern. We show the principal functionality of the multi-spot generator. Furthermore constrains of this setup are demonstrated. The multi spot scanner is used for micro structuring of silicon with a nanosecond diode pumped solid state laser. The ablation rate and structure quality are compared to single spot processing. IntroductionThe ongoing development of new laser sources with a continual increase in laser power enables higher production speeds for example in the application of micro machining, hole drilling or perforation. The processing speed however is still limited by the maximum speed of positioning systems. State-of-the-art laser systems provide high pulse energies which normally exceed the laser ablation threshold energy density by several orders of magnitude. Additionally the ablation quality decreases with increasing energy density clearly over the ablation threshold. In this case energy is wasted which leads to a decrease in the throughput and efficiency. Parallelizing a laser process can increase the throughput of the production. This can be done with a so-called array generator, an optical system that splits a light beam in a 1 -or 2-dimensional array of beamlets [1,2]. In the field of laser materials processing, optical measuring technology, biotechnology and medicine [3] many new applications for efficient array generators can be found. A number of optical systems and elements, such as spatial light modulators (SLM) [4], diffractive optical elements (DOE) [5] or micro lens arrays (MLA) [6,7,8] have been examined for generation of multiple spot arrays for laser micro machining applications.