Measurement of plasma and shock-wave dynamics and properties inside holes during laser drilling of metals

Abstract

Laser material processing can be 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 a 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 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 less than 1 µm. The results are compared with models for shock-wave and plasma propagation in non-confined environments. Emission spectroscopy is carried out during the expansion of the plasma inside the drilled hole allowing the determination of electron density by Stark broadening.Laser material processing can be 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 a 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 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 less than 1 µm. The results are compared with models for shock-wave and plasma propagation in non-confined environments. Emission spectroscopy is carried out during the expansion of the plasma inside the drilled hole allowing the...