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Proceedings Paper

Fabrication of micro-lenses using excimer laser ablation by means of laser-generated grey-tone-masks
Author(s): T. Klotzbuecher; D. Dadic
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Paper Abstract

Micro-lenses, including Fresnel-Lenses, were fabricated by excimer laser ablation of polymers by means of lasergenerated grey-tone-masks. The smallest reproducible holes that could be fabricated by excimer laser ablation (193 nm, 1 J/cm2) of chromium-on-quartz (thickness 50-100 nm) were around 3 μm, the pitch of which should be at least at the same value to ensure a reproducibility of hole-arrays. To achieve acceptable ablation times during the fabrication of the grey-tone-masks, on-the-fly ablation instead of step-and-repeat technique was used, operating the laser at a constant pulse repetition rate <30 Hz with a continuously moving quartz-substrate. In this way and using different encoding techniques it was possible to generate at least 11 different grey-tones. The available grey-tones were used to generate grey-tone-masks for ablation of Polymethylmethacrylate (PMMA) and Polycarbonate (PC). For that, fluences in the range of 0.07-0.14 J/cm2 could be applied, corresponding to a value of 1.25 J/cm2 on the workpiece without grey-tonemask and a value lying well below the damage threshold of the chromium mask. Refractive micro-lenses fabricated in this way did not show a good imaging quality, since 11 grey-tones is less than required to generate a continuous surface profile over the full diameter of the lens during ablation and the achievable aspect ratio is limited with the small fluences. However, flat diffractive micro-lenses of the Fresenel type with a quasi-continuously surface profile could be fabricated in a sufficient manner. This can be attributed to the fact that each segment of the Fresenel-lenses can be encoded by 11 grey-tones, leading to much smoother surface reliefs and to a sufficient imaging quality.

Paper Details

Date Published: 23 February 2010
PDF: 11 pages
Proc. SPIE 7585, Laser-based Micro- and Nanopackaging and Assembly IV, 75850C (23 February 2010); doi: 10.1117/12.845476
Show Author Affiliations
T. Klotzbuecher, Institut für Mikrotechnik Mainz GmbH (Germany)
D. Dadic, Institut für Mikrotechnik Mainz GmbH (Germany)

Published in SPIE Proceedings Vol. 7585:
Laser-based Micro- and Nanopackaging and Assembly IV
Wilhelm Pfleging; Yongfeng Lu; Kunihiko Washio; Jun Amako; Willem Hoving, Editor(s)

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