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Proceedings Paper

Heat-affected zone in microdrilling of metals by femtosecond laser pulses
Author(s): E. Audouard; R. LeHarzic; Nicolas Huot; Pierre Laporte; S. Valette; R. Fourtunier
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Paper Abstract

Several works on laser-matter interaction has shown the differences in sizes for the Heat Affected Zone (HAZ) obtained with nanosecond and femtosecond regimes in laser cutting or drilling. To understand more clearly the basic phenomena that occur in femtosecond regime during the absorption of light by matter, and specially in the case of metals, we have developed both an experimental and a theoretical approach. We use a new method aimed at quantifying the dimensions of the HAZ, using thin-down samples which are micro-drilled and then observed by a transmission electronic microscopy (TEM) technique. The grain size in the samples is analysed near the micro-holes. According to theoretical studies, the thermal diffusion is due to the smaller value of the electron specific heat compared to the lattice one. The thermal diffusion length is found to be a few hundred of nanometers in the case of metals. We use a thermal model to describe the heat diffusion in the sample in order to obtain a theoretical estimation of the HAZ. Holes are drilled in Aluminum using nanosecond and femtosecond laser pulses and characterized by Transmission Electronic Microscopy (TEM). The method for quantifying the dimensions of the heat affected zone (HAZ) surrounding micro-holes is based on the analyze of the grain size evolution. The experiments are using the same Ti-Sapphire laser source (1 kHz, 800 nm). The regeneratively amplified ultra-short pulses (150 fs) are utilized at a low fluence regime (typically 0.01-0.5 mJ/pulse), while the longer pulses (ns) are obtained from the regenerative amplifier without oscillator seeding (0.5 mJ,τ approximately 7-8 ns). The main conclusion is that a 40 micrometers wide HAZ is induced by nanosecond pulses, whereas the femtosecond regime does not produce any TEM observable HAZ. It has to be noticed that the width of the femtosecond HAZ is roughly less than 2 micrometers , which is our observation limit. These results are in agreement with theoretical predictions.

Paper Details

Date Published: 13 September 2002
PDF: 7 pages
Proc. SPIE 4760, High-Power Laser Ablation IV, (13 September 2002); doi: 10.1117/12.482053
Show Author Affiliations
E. Audouard, Univ. Jean Monnet Saint-Etienne (France)
R. LeHarzic, Univ. Jean Monnet Saint-Etienne (France)
Nicolas Huot, Univ. Jean Monnet Saint-Etienne (France)
Pierre Laporte, Univ. Jean Monnet Saint-Etienne (France)
S. Valette, Ecole Nationale Superieure des Mines de Saint-Etienne (France)
R. Fourtunier, Ecole Nationale Superieure des Mines de Saint-Etienne (France)

Published in SPIE Proceedings Vol. 4760:
High-Power Laser Ablation IV
Claude R. Phipps, Editor(s)

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