We report on our recent developments in the field of ultrashort pulse welding of transparent and transparent to opaque materials. Based on recent trends in diverse branches such as biomedicine or consumer electronics we obtain a demand of reliable and sustainable joining technologies. This can be addressed by the adhesive free and localized laser joining technique using ultrashort laser pulses. Nonlinear absorption as well as heat accumulation within the focal region generate localized joints that are long term stable. On the other hand, the short focal tolerance and small gap size that can be bridged leads to high requirements for the surface quality of the weld partners hindering a cost-effective industrial usage. To overcome these limitations, spatial and temporal beam shaping of the ultrashort laser pulses is used. Based on temporal energy modulation together with the world´s first optics for ultrashort pulse welding (Top Weld optics) much better weld performance in terms of focal tolerance and gap bridging is achieved. The process allows for the bridging of gaps up to 10μm and a focal tolerance of up to 300μm which is several times higher compared with Gaussian focusing (4μm gap size, 80μm focal tolerance). This enables a highly reproduceable welding process even for larger sample dimensions e.g. in the field of architecture. Furthermore, to ensure welding in industrial environment with high throughput a simple process diagnostic based on monitoring the process illumination is presented.
During the last years processing of transparent materials by ultrashort laser pulses has gained interest. Spatial and temporal pulse shaping has already proven its potential for advances, widening existing and opening new application fields. The paper focuses on supporting the application development by extending pump-probe diagnostics via combining pulse shaping capabilities, dynamical beam positioning, processing at elevated repetition rates, energy modulation and high temporal resolution over an essentially infinite range of delay. Applying these capabilities gives inside into effects resulting from spatial and temporal shaping, on the laser matter interaction of individual and of a multitude of pulses, the latter typically effective on larger scales due to accumulation. The influence of beam shaping and processing parameters on the dynamic development of the interaction zone in multi pulse exposure highlights the potential of such diagnostic tools. Observations relevant for development of transparent materials processing ultrafast lasers by absorption induced inside of the workpiece are presented. Initiation and development of cracks as a major aspect in brittle materials processing can be analyzed in detail. Pump-probe polarization microscopy for transient stress birefringence observation reveals that both, pressure waves and temperature gradients from accumulation, are of major importance in scaling industrial processing. Considering these findings facilitates addressing different application fields, illustrated by examples on ultrafast welding and selective etching by shaped beams.
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