Excimer lasers turning flexible -variable Marking with Micro Mirror Devices

摘要

Higher and higher through-puts in marking industry are todays requirements: especially part-by-part varying markings like serial numbers, weight, date or barcodes are asked for. Taking advantage of the photosensitivity of commonly used opigments like titanium oxide marking industry is interested in turning existing excimer laser marking processes into a flexible, high-speed on-the-fly marking technique. Current laser marking techniques like direct writing using a scanned laser beam offer flexibility but have limitations with sensitive materials like paper or plastics. Excimer laser mask projection technique is best suitable for sensitive materials but up to now has the drawback of invariability due to fixed transmittive masks. The Fraunhofer IWS developed a marking system using excimer laser mask projection with a micro mirror device (MMD) as 'flexible mask'. With up to 2 million separate controllable micro mirrors the MMD provides variability: with every single laser pulse a new complex marking can be achieved. To demostrate the capabilities the FhG IWS used a 308nm excimer laser and a reflective phase-shifting mask from FhG IMS. It was possible to generate free-programmable, high-contrast markings on materials like paper and plastic. Furthermore, it could be shown that the technique is also usable to generate 3D structures in PI. Result of the studies is the development of a very fast marking technique using MMDs in combination with short wavelength and short pulse lasers. It also has high potential in 3D laser micromachining.