High throughput surface structuring with ultrashort pulses in synchronized mode with fast polygon line scanner

High precision laser micromachining requires an exact synchronization of the laser pulse train with the mechanical axes of the motion system to ensure for each single pulse a precise control of the laser spot position - on the target. For ultra short pulsed laser systems this was already demonstrated with a conventional two-axis galvanometer scanner. But this solution is limited by the scanner architecture to a marking speed of about 10m/s with a maximum scan line length of about 100mm. It is therefore not suited for average powers far beyond 10W when working at the optimum point with highest removal rate and machining quality is desired. A way to overcome this limitation is offered by polygon line scanners which are able to realize much higher lateral speeds at large scan line lengths. In this work we will report on the results with a polygon line scanner having a maximum moving spot velocity of 100m/s, a scan line length of 170mm, spot diameters of 45µm (1064nm) and 22µm (532nm) together with a 50W, 10-ps laser system. The precise control of the laser spot position i.e. the synchronization is realized via the new SuperSyncTM technology. Decoating, perforation and 3D patterning will act as benchmark processes to evaluate this scanning technology

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

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 100W 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 40W and a spot radius of about 25lm, if a polygon line scanner, offering fast scanning speeds, is used. A further scale-up into the 100W 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 100m/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

CIGS thin-film solar module processing: case of high-speed laser scribing

In this paper, we investigate the laser processing of the CIGS thin-film solar cells in the case of the high-speed regime. The modern ultra-short pulsed laser was used exhibiting the pulse repetition rate of 1 MHz. Two main P3 scribing approaches were investigated – ablation of the full layer stack to expose the molybdenum back-contact, and removal of the front-contact only. The scribe quality was evaluated by SEM together with EDS spectrometer followed by electrical measurements. We also modelled the electrical behavior of a device at the mini-module scale taking into account the laser-induced damage. We demonstrated, that high-speed process at high laser pulse repetition rate induced thermal damage to the cell. However, the top-contact layer lift-off processing enabled us to reach 1.7 m/s scribing speed with a minimal device degradation. Also, we demonstrated the P3 processing in the ultra-high speed regime, where the scribing speed of 50 m/s was obtained. Finally, selected laser processes were tested in the case of mini-module scribing. Overall, we conclude, that the top-contact layer lift-off processing is the only reliable solution for high-speed P3 laser scribing, which can be implemented in the future terawatt-scale photovoltaic production facilities