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Proceedings Paper

Focal length stabilization of a tunable lens integrated focus shifting unit
Author(s): Gregory Eberle; Benjamin Boesser; Konrad Wegener
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Paper Abstract

A focus shifting unit integrated with a tunable lens allows for rapid response times, high accuracy, small footprint and simple controllability without the need for any translational mechanics. The focus shifting unit is designed for laser material microprocessing applications where tolerances of a few micrometers are required. However, the optical fluid inside the tunable lens can be severely altered by long term thermal influences from the environment and high powered laser beams. Utilizing the working principles of a cylinder lens, a discrete proportional-integral-derivative controller with an anti-reset windup is simulated and designed for offline regulation of the focal length of the tunable lens. This allows for integration into a three-dimensional scanhead system to reliably deflect the focused laser spot at the workpiece level over long periods of time, i.e. > 8 hours. Deviation of the focal length of the tunable lens is identified by the cylinder lens through ellipticity of a probe laser beam. The focal length is subsequently corrected by altering the input current into the tunable lens by means of the control system which is based on numerical methods. The thermal behavior of the tunable lens, system identification and synthesis of the controller, design of the focus shifting optical system and validation of the controller are studied.

Paper Details

Date Published: 6 March 2014
PDF: 9 pages
Proc. SPIE 8967, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX, 89670G (6 March 2014); doi: 10.1117/12.2035104
Show Author Affiliations
Gregory Eberle, ETH Zürich (Switzerland)
Benjamin Boesser, ETH Zürich (Switzerland)
Konrad Wegener, ETH Zürich (Switzerland)
Inspire AG (Switzerland)

Published in SPIE Proceedings Vol. 8967:
Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX
Yoshiki Nakata; Xianfan Xu; Stephan Roth; Beat Neuenschwander, Editor(s)

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