Measurement of Plasma and Shock-Wave Dynamics and Properties Inside Holes during Laser Drilling of Metals
Authors:
Ingomar Kelbassa, Lehrstuhl Fuer Lasertechnik, Rwth Aachen University; Aachen Germany
Kurt Walther, Lehrstuhl F Lasertechnik, Rwth Aachen; Aachen Germany
Martin Hermans, Lehrstuhl Fuer Lasertechnik, Rwth Aachen University; Aachen Germany
Michel Kaminsky, Lehrstuhl Fuer Lasertechnik, Rwth Aachen University; Aachen Germany
Mihael Brajdic, Lehrstuhl Fuer Lasertechnik, Rwth Aachen University; Aachen Germany
Presented at ICALEO 2008

Laser material processing is influenced by plasma formation and dynamics such as plasma shielding or plasma supported ablation. A novel method for investigating in-situ plasma and shock-wave dynamics inside a confined space like a laser drilled hole in metals is presented. A specific sample preparation with prepared mock-up holes including a transparent material as window is used. By use of high speed imaging and spectroscopy a time and spatially resolved monitoring of the optical emissions of plasma and shock-waves is realized during drilling stainless steel and aluminum with ns-pulsed laser radiation. Spatial intensity distributions and the velocities of the shock-waves and the plasma are measured inside the holes with a temporal resolution of 1 ns and a spatial resolution of < 1 μm. The results are compared with models for shock-wave and plasma propagation. Emission spectroscopy is carried out during the expansion of the plasma inside the drilled hole allowing the determination of electron density by Stark broadening.