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Proceedings Paper

Femtosecond pulse laser ablation of metallic, semiconducting, ceramic, and biological materials
Author(s): Wolfgang Kautek; Joerg Krueger
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Paper Abstract

Production of holes and grooves of < 30 micrometers diameter with high aspect ratio value is a delicate task either for mechanical tools, or for conventional nanosecond pulse lasers like e.g. pulsed Nd:YAG or excimer lasers. They later tend to cause microcracks extending from an annular melting zone, or substantial disruption, respectively. Experimental results are presented which demonstrate that the development of intense ultrashort pulse laser systems (>> 1012 W cm-2, (tau) < 1 ps) opens up possibilities for materials processing by cold plasma generation and ablation of metals, semiconductors, ceramics, composites, and biological materials. A femtosecond and a nanosecond dye laser with pulse durations of 300 fs (< 200 (mu) J) and 7 ns (< 10 mJ), and center wavelengths at 612 and 600 nm, respectively, both focused on an area of the order of 10-5 cm2, have been applied either to absorbing substrates, like polycrystalline gold, silicon (111), aluminum nitride ceramics, or transparent materials, like synthetic and human dental hydroxyapatite composites, bone material, and human cornea transplants. The fs-laser generates its own absorption in transparent materials by a multiphoton absorption process, and thus forces the absorption of visible radiation. Because the time is too short (< ps) for significant transport of mass and energy, the beam interaction generally results in the formation of a thin plasma layer of approximately solid state density. Only after the end of the subpicosecond laser pulse, it expands rapidly away from the surface without any light absorption and further plasma heating. Therefore, energy transfer (heat and impulse) to the target material, and thermal and mechanical disruption are minimized. In contrast to heat- affected zones (HAZ's) generated by conventional nanosecond pulse lasers of the order of 1 - 10 micrometers , HAZ's of less than 0.02 micrometers were observed.

Paper Details

Date Published: 7 September 1994
PDF: 12 pages
Proc. SPIE 2207, Laser Materials Processing: Industrial and Microelectronics Applications, (7 September 1994); doi: 10.1117/12.184768
Show Author Affiliations
Wolfgang Kautek, Bundesanstalt fuer Materialforschung und -pruefung (Germany)
Joerg Krueger, Bundesanstalt fuer Materialforschung und -pruefung (Germany)

Published in SPIE Proceedings Vol. 2207:
Laser Materials Processing: Industrial and Microelectronics Applications
Eckhard Beyer; Maichi Cantello; Aldo V. La Rocca; Lucien Diego Laude; Flemming O. Olsen; Gerd Sepold, Editor(s)

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