Selective laser melting of copper using ultrashort laser pulses at different wavelengths

Additive manufacturing gained increasing interest during the last decade due to the potential of creating 3D devices featuring nearly any desired geometry. One of the most widely used methods is the so-called powder bed method. In general, conventional cw and pulsed laser sources operating around 1030 nm and CO2 lasers at 10.6 mm are usually applied. Among other materials like polymers, these systems are feasible for several metals, alloys and even ceramics, but easily reach their limitation at a wide range of other materials, regarding required absorption and intensity. In order to overcome these limits, ultrashort pulse laser systems are one approach. Due to the increased peak power and ultrashort interaction times within the femtosecond and picosecond time range, materials with extraordinary high melting points, increased heat conductivity or new composites with tailored specifications are coming into reach. Moreover, based on the nonlinear absorption effect, also transparent materials can be processed. Here, we present the selective laser melting of pure copper using ultrashort laser pulses. This work involves a comparative study using 500 fs pulses at processing wavelengths of 515 nm and 1030 nm. The repetition rate of the applied laser system was varied within the MHz range in order to exploit heat accumulation. By using the ultrashort interaction times and tailoring the repetition rate, the induced melt pool can be significantly optimized yielding robust copper parts revealing thin-wall structures in the range below 100 mm.