Refractive Beam Shaping: From Maxwell's Equations To Products And Applications In Laser Materials Processing

Laser materials processing is an enabling technology in many industries, most prominently automotive, semiconductor technology, flat panel display production1, solar cell technology, medicine, metalworking, and plastics-working. Typical laser-based processes include: welding, soldering, cutting, drilling, laser annealing, micromachining3, ablation4, and microlithography. Besides choosing a suitable laser source, selecting the adequate beam-shaping optics for the generation of the appropriate beam profile is crucial.

Compared to classical optics, micro-optics possesses several advantages in achieving best performance for an application. The most widely used intensity distributions for micro-optics are square or rectangular light fields or light lines with homogeneous profiles in one or two dimensions. With micro-optics, beam lines that result in superior homogeneity and efficiency can be produced. The use of micro-optics in laser materials processing can also result in products with higher quality and performance, as well as increased throughput in the production line. Additionally, novel laser-based processes can be developed that are not possible with traditional optics approaches. Processes involving homogeneous illumination of masks and subsequent imaging, as well as laser direct structuring with top-hat profiles, are evaluated.

This article will present the whole devolution from optical design and engineering to products and applications. A new software tool, founded on Maxwell's equations, is introduced that takes into account all-important physical aspects of the beamshaping task. Various beam-shaping principles like phase shifting for single-mode lasers, beam mixing for multi-mode lasers, and other beam transformation schemes are discussed. Based on the latest production technologies using computer-aided design (CAD), free-form microlens surfaces can be structured cost-effectively on a wafer basis. Thus, theoretically optimized surfaces can be transformed with high precision into a wide range of materials. Typical products, their beam profiles, and the respective application results are also shown for optical microlithography, micromachining with Nd:YAG lasers, and silicon (Si) thin-film annealing for flat panel display production.

SOURCE: LIMO Lissotschenko Microoptic Inc.