Effect of air breakdown on short-pulsed laser drilling

T. V. Kononenko; S. M. Klimentov; V. I. Konov; F. Dausinger

doi:10.1117/12.675005

26 April 2006 Effect of air breakdown on short-pulsed laser drilling

T. V. Kononenko, S. M. Klimentov, V. I. Konov, F. Dausinger

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Proceedings Volume 6161, International Conference on Lasers, Applications, and Technologies 2005: Laser-Assisted Micro- and Nanotechnologies; 616106 (2006) https://doi.org/10.1117/12.675005
Event: International Conference on Lasers, Applications, and Technologies 2005, 2005, St. Petersburg, Russian Federation

Abstract

Laser-induced air breakdown near a steel target surface ablated by short (300 ps and 10 ns) laser pulses was studied with optical emission spectroscopy to determine conditions of the breakdown ignition and time-integrated spatial localization of the laser plasma. The air breakdown was found to occur in a wide range (5-1000 mbar) of ambient air pressures, if the energy density exceeds ~10 J/cm² for the IR radiation (λ=1078 nm) and ~40 J/cm² for the visible light (λ=539 nm). Both the crater bottom ablation and evaporation of residual metal droplets suspended in air can ignite the low-threshold air breakdown. The experiments on deep laser drilling of steel demonstrate a sharp decrease of the drilling rate and simultaneous increase of the crater entrance diameter after the crater depth reaches a critical value. The critical crater depth increases with the applied energy density, under decrease of the ambient air pressure and under shortening of the laser pulses. The critical depth correlates with longitudinal shift of the time-integrated maximum plasma emission away from the ablated surface. Noticeable etching of the crater walls by the laser-induced plasma is observed, if movement of the plasma plume away from the ablated surface is stopped by the ambient air before the plasma leaves the crater. Interaction of the plasma with the crater walls should block ejection of the melt phase which is proposed as a reason for the observed sharp decrease of the drilling rate in a deep crater.

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T. V. Kononenko, S. M. Klimentov, V. I. Konov, and F. Dausinger "Effect of air breakdown on short-pulsed laser drilling", Proc. SPIE 6161, International Conference on Lasers, Applications, and Technologies 2005: Laser-Assisted Micro- and Nanotechnologies, 616106 (26 April 2006); https://doi.org/10.1117/12.675005

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KEYWORDS

Plasma

Laser drilling

Picosecond phenomena

Laser ablation

Iron

Ionization

Laser damage threshold

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