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Proceedings Paper

Nanosecond laser-induced explosive boiling studied by photoacoustic and plume transmission techniques
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Paper Abstract

A model experimental "thin variable thickness transparent liquid layer on opaque (absorbing) solid substrate" geometry has been chosen to study explosive boiling and lift-off of a pre-deposited 2-propanol (isopropanol, IPA) layer on a crystalline Si substrate heated by a nanosecond KrF excimer laser using contact photoacoustic and optical plume transmission techniques. The threshold-like transition from the low-amplitude (sub-MPa) bipolar to the intense (near GPa) unipolar temporal shape of acoustic transients has been observed above the ablation threshold of 0.17 J/cm2 ("universal" for micron-thick IPA layers used) due to sub-nanosecond explosive near-critical expansion and boiling in the nanometer-thick liquid IPA sub-layer near the film/substrate interface heated by conduction from the Si substrate. This pressure build-up exceeding many times the critical pressure of 2-propanol (4.8 MPa) exerted a reactive force on the cooler liquid overlay of the IPA layer and accelerated it to lift-off (ablative plume) velocities from several m/s to several tens m/s depending on the film thickness, while the initial expansion velocity of the superheated IPA sub-layer was about 1 km/s. In a good agreement with experimental data, calculations of the IPA/substrate interface temperatures versus laser fluence have shown near-critical state of the IPA sub-layer near the ablation threshold. These data allow testing the general sub-surface explosive boiling mechanism, characteristic for pulsed laser ablation of both opaque and weakly-absorbing materials.

Paper Details

Date Published: 20 September 2004
PDF: 9 pages
Proc. SPIE 5448, High-Power Laser Ablation V, (20 September 2004); doi: 10.1117/12.563173
Show Author Affiliations
Sergey I. Kudryashov, Arkansas State Univ. (United States)
Susan D. Allen, Arkansas State Univ. (United States)

Published in SPIE Proceedings Vol. 5448:
High-Power Laser Ablation V
Claude R. Phipps, Editor(s)

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