Laser surface structuring with 100 W of average power and sub-ps pulses

Abstract

High throughput still represents a key factor for industrial use of ultrashort pulses in the field of surface structuring. Reliable systems with average powers up to 100 W are today available. It has already been proved that metals, especially steel having a low threshold fluence, can be machined with excellent surface quality at average powers of more than 40 W and a spot radius of about 25 μm, if a polygon line scanner, offering fast scanning speeds, is used. A further scale-up into the 100 W regime should be possible for metals showing a threshold fluence of about 0.2 J/cm2 or higher. But, it will lead to problems with heat accumulation in the case of steel and a straight forward scale-up is not possible. In order to keep a good surface quality, the machining strategy has to be adapted. A maximum flexibility can be obtained with an “interlaced” mode by using very high marking speeds of several 100 m/s and repetition rates of several tenths of MHz. As this is at the edge of today available technologies, alternative strategies are additionally investigated. Enlarging the spot size represents the most simple approach to reduce the heat accumulation in the case of steel but also multispots represent an attractive alternative.