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Using lasers for permanent markings is a well-known method and standard in many areas in industrial manufacturing. Various processes on all kinds of materials are used to achieve durable markings, where the content is often serial numbers, codes and company logos. Whereas laser marking processes are mostly easy to handle it becomes challenging if the markings need to fulfill the requirements of the medical industry. The demand for markings in the medical industry is increasing because of the regulations in this sector. The labelling of medical devices with a traceable Unique Device Identification (UDI) code has become mandatory. Laser marking of medical steel needs to fulfill certain criteria where corrosion resistance, a toxicologically uncritical surface and good contrast, are key factors. Standard laser marking systems are reaching their limits to fulfill these criteria. The best choice to accomplish this challenge is the usage of ultrashort pulsed (USP) lasers. The process using USP lasers, fulfilling the criteria of medical industry, is often called “black marking”. We use the TruMicro Mark 2030 G2 S. This laser has the advantage of full flexibility of the important parameters, such as pulse energy, pulse frequency and pulse duration. Due to the great necessity for reliable medical devices, we investigate the effect of varying different laser parameters on the resulting structures of the black marking process on stainless steel in an experimental study. Analyzed is the dependency of the resulting structures on the energy density by varying the laser spotsize. This is adjusted by a parameter in the marking software and can be set continuously. The dependency of the resulting structures on the pulse duration is investigated by varying the pulse duration. The pulse duration is adjusted by a parameter in the marking software and can be tuned in the range of 400 fs to 20 ps at 100 fs increments. The fundamental parameters like beam quality, beam pointing or energy stability are not affected by changing the pulse duration. The fast switching time of < 800 ms enables for intra-process tuning of the temporal energy deposition. Analyzing the results by a Scanning Electron Microscope (SEM) reveals different surface structures. The structures change in its appearance, periodicity, and groove depth. Various of the described structures can give a permanent black contrast and fulfill the requirements of medical industry.
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