TECHNICAL PAPERS: Micro/Nanoscale Heat Transfer

Observation of Femtosecond Laser-Induced Ablation in Crystalline Silicon

[+] Author and Article Information
Tae Y. Choi

Institute of Energy Technology, Swiss Federal Institute of Technology Zurich, Zurich, CH-8092 Switzerlande-mail: choi@ltnt.iet.mavt.ethz.ch

Costas P. Grigoropoulos

Department of Mechanical Engineering, University of California, Berkeley, Berkeley, CA 94720-1740e-mail: cgrigoro@me.berkeley.edu

J. Heat Transfer 126(5), 723-726 (Nov 16, 2004) (4 pages) doi:10.1115/1.1795224 History: Received April 22, 2003; Revised February 27, 2004; Online November 16, 2004
Copyright © 2004 by ASME
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Temporal evolution of calculated surface electron density and reflectivity at λ=400 nm with no consideration of phase change. (Note the electron density at 0.5 ps is 2×1022 cm−3.) The laser fluence is 1.5 J/cm2. The critical density for lattice instability has been revealed theoretically at 1022 cm−3 (Ref. 5).
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Schematic diagram of experimental setup (DM: dichroic mirror; NLC: nonlinear crystal; λ/4: quarter wave plate; L: lens; M: Mirror). The pump beam (solid line) and probe beam (dotted line) are normally incident on the sample.
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Time-resolved surface images at fluence of 1.5 J/cm2. Highly reflecting phase is identified below 1 ps. The ablation starts at around 10 ps.
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(a) Short time scale and (b) longer time scale time-resolved surface reflectivity traces. Reflectivity at the early stage approaches that of liquid silicon.
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Reflectivity as a function of layer thickness for liquid silicon and solid-state plasma. (The low plasma density, 2×1022 cm−3, is utilized for predicting the relectivity at 0.5 ps.)
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Comparison of time-resolved image sequence (a) 2.9 and (b) 4.6 J/cm2. The bright spot at the center of the irradiated zone persists longer at higher laser fluence.
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Surface images taken at 500 ps for different energy densities for (a) 0.4, (b) 1.5, (c) 2.9, and (d) 4.6 J/cm2. Peripheral dark rings at higher fluences correspond to rarefaction wave toward the sample surface.




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