Heat-induced structure formation in metal films generated by single ultrashort laser pulses

Jürgen Koch; Claudia Unger; Boris N. Chichkov

doi:10.1117/12.908561

20 February 2012 Heat-induced structure formation in metal films generated by single ultrashort laser pulses

Jürgen Koch, Claudia Unger, Boris N. Chichkov

Proceedings Volume 8244, Laser-based Micro- and Nanopackaging and Assembly VI; 824408 (2012) https://doi.org/10.1117/12.908561
Event: SPIE LASE, 2012, San Francisco, California, United States

Abstract

Ultrashort pulsed lasers are increasingly used in micromachining applications. Their short pulse lengths lead to well defined thresholds for the onset of material ablation and to the formation of only very small heat affected zones, which can be practically neglected in the majority of cases. Structure sizes down to the sub-micron range are possible in almost all materials - including heat sensitive materials. Ultrashort pulse laser ablation - even though called "cold ablation" - in fact is a heat driven process. Ablation takes place after a strong and fast temperature increase carrying away most of the heat with the ablated particles. This type of heat convection is not possible when reducing the laser fluence slightly below the ablation threshold. In this case temperature decreases slower giving rise to heat-induced material deformations and melt dynamics. After cooling down protruding structures can remain - ablation-free laser surface structuring is possible. Structure formation is boosted on thin metal films and offers best reproducibility and broadest processing windows for metals with high ductility and weak electron phonon coupling strength. All approaches to understand the process formation are currently based only on images of the final structures. The pump-probe imaging investigations presented here lead to a better process understanding.

Citation Download Citation

Jürgen Koch, Claudia Unger, and Boris N. Chichkov "Heat-induced structure formation in metal films generated by single ultrashort laser pulses", Proc. SPIE 8244, Laser-based Micro- and Nanopackaging and Assembly VI, 824408 (20 February 2012); https://doi.org/10.1117/12.908561

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