Product Code: ICA10_P189

Laser Micro Processing using a High Repetition Rate Femto Second Laser
Authors:
J. Schille, University of Applied Sciences Mittweida, Laser Application Centre, The University of Manchester, The Photon Sciences Institute & CEAS; Mittweida Germany
U. Loeschner, University of Applied Sciences Mittweida, Laser Application Centre; Mittweida Germany
R. Ebert, University of Applied Sciences Mittweida, Laser Application Centre; Mittweida Germany
P. Scully, The University of Manchester, The Photon Sciences Institute & CEAS; Manchester
N. Goddard, The University of Manchester, The Photon Sciences Institute & CEAS; Manchester
H. Exner, University of Applied Sciences Mittweida, Laser Application Centre; Mittweida Germany
Presented at ICALEO 2010

The paper will present an overview about mechanism and effects using a high repetition rate femto second laser in laser micro processing and its applications. First experimental studies show novel mechanisms in laser matter interaction with the repetition rate as one of the mainly influencing parameter. Depending on temporal distances between consecutive femto second laser pulses, either heat accumulation or particle shielding effects were detected. Heat accumulation causes higher mean temperatures of the work piece, locally encircled the laser working zone accompanied by better absorption conditions and lowered ablation thresholds (fig. a). For laser
processing with repetition rates in ranges of some 100 kHz phenomena of particle and plasma shielding was found. Furthermore the occurrence of laser induced periodical surface structures, such as ripple formations and conical micro structures, was observed due to the high average laser energy input and accumulative effects (fig. b). Joining high repetition rate laser technology together with innovative high speed beam deflection systems, significantly higher ablation rates and short processing times were achieved. Exemplarily
demonstrated in 3D micro structuring, processing times were reduced more than 40 times compared to fs laser processing using repetition rates of some kHz. In consequence, prospectively high machining throughputs can be reached, which attract increasing interest of the novel technology in industrial
applications. In the work results of laser micro processing of metals, e.g. steel, copper and aluminium, with both, a resonant scanner and a fast galvo scanner will be presented to demonstrate the possibilities and limits of the new technology in Rapid Micro Tooling (figure c, d). (a) ablation threshold for different metals depending on the repetition rate (b) laser induced periodical
surface structures on stainless steel surface (LIPSS) (c) cross section of line scan ablation on stainless steel (d) 3D test structure shows a hemisphere, pyramidal frustum, triangle and rectangular prism; ablation depth: 100μm; processing time: 350 sec.