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Proceedings Paper

Ablation of amorphous Polyethy(ethyl)letone (PEEK) by a femtosecond Ti:sapphire laser
Author(s): Qianliang Li; Walter Perrie; Yue Tang; Olivier Allegre; Janet Ho; Paul Chalker; Zhaoqing Li; Stuart P. Edwardson; Geoff Dearden
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Paper Abstract

Laser micro-machining of amorphous PEEK has been demonstrated with 180 fs/1 kHz NIR (775 nm) and NUV (387 nm) laser pulses. The single pulse ablation threshold was found to be 2.01 ± 0.05 J/cm2 and 0.23 ± 0.02 J/cm2 at 775 nm and 387 nm respectively. The significant difference in ablation threshold is due to the requirement for 3-photon absorption at 775 nm, where PEEK is transparent while significant linear absorption within the material bandgap occurs at 387 nm, enhancing 2-photon absorption. A high 2-photon absorption coefficient, measured to be β387 ~ 38 cm GW-1 supports this view while at the bandgap edge, 400 nm, β400 ~ 0.7 cm GW-1. Multi-pulse exposure yields incubation coefficients of S775 = 0.72 ± 0.01 and S387 = 0.85 ± 0.02 hence incubation is significantly reduced in the NUV. Ablation of PEEK with NUV fs pulses demonstrates much reduced melting and re-deposition, thus precision NUV polymer micromachining is accomplished while laser induced periodic surface structures (LIPSS) with pitch Λ < 0.4 μm are observed at the base of ablated regions. Scanned areas exhibit white light diffraction due to this sub-micron periodic surface modulation. With the aid of a phase only spatial light modulator, multi-beam NUV micro-structuring is achieved, speeding micro-processing while reaching a line width < 4 μm with NA = 0.4 objective.

Paper Details

Date Published: 2 March 2020
PDF: 9 pages
Proc. SPIE 11268, Laser-based Micro- and Nanoprocessing XIV, 112680L (2 March 2020); doi: 10.1117/12.2543735
Show Author Affiliations
Qianliang Li, Univ. of Liverpool (United Kingdom)
Walter Perrie, Univ. of Liverpool (United Kingdom)
Yue Tang, Univ. of Liverpool (United Kingdom)
Olivier Allegre, The Univ. of Manchester (United Kingdom)
Janet Ho, US Army Research Lab. (United States)
Paul Chalker, Univ. of Liverpool (United Kingdom)
Zhaoqing Li, The Univ. of Manchester (United Kingdom)
Stuart P. Edwardson, Univ. of Liverpool (United Kingdom)
Geoff Dearden, Univ. of Liverpool (United Kingdom)

Published in SPIE Proceedings Vol. 11268:
Laser-based Micro- and Nanoprocessing XIV
Udo Klotzbach; Akira Watanabe; Rainer Kling, Editor(s)

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