Product Code: ICAL09_M106

Optical Emission Imaging and Spectroscopy during Femtosecond Laser Ablation of Thin Metal Films on Flexible Polymer Substrates
Authors:
Jan F. Duesing, Laser Zentrum Hannover; Hannover Germany
David J. Hwang, University of California at Berkeley; Berkeley CA USA
Costas Grigoropoulos, University of California at Berkeley; Berkeley CA USA
Andreas Ostendorf, University of California at Berkeley; Berkeley CA USA
Rainer Kling, Laser Zentrum Hannover; Hannover Germany
Presented at ICALEO 2009

Thin film processes with lasers are becoming more and more important for various fields of technical applications, such as photo voltaics and flexible electronics. While ablation of thin films with nanosecond lasers has been already established in industrial processes, the usage of ultrashort pulsed lasers opens new possibilities and applications due to the recent progress in the development of new laser sources. The main advantage in the material ablation with ultrashort laser pulses is the reduced thermal damage and consequent higher quality of the remaining structures. In this experimental investigation thin metal films (Pd, Cr, and Ti) on flexible polymer substrates are ablated by single femtosecond laser pulses. Different ablation regimes are identified and, above a certain threshold, the thin films could be ablated with a single pulse and no visible damage of the substrate. By use of an intensified CCD camera and a spectrometer the propagation and the spectrum of the ablation plume is recorded with a temporal resolution of 2 ns. This data is combined with observations in scanning electron microscope images of the ablation craters. It is shown that, depending of the ablation regime, the material propagates in distinctive material waves with characteristic emission spectrums. Above the single pulse ablation threshold the plume typically splits into two components, a fast component (up to several km/s) with a mainly atomic emission spectrum and a slow component (about 200 m/s) with a broad continuum spectrum likely due to thermal radiation of hot nanoparticles. In this work, these main ablation trends are pointed out and the specific differences between the film materials are analyzed. The results of this study provide insights into the physical mechanisms of ultrafast laser ablation of thin metal films from flexible polymer substrates.