Focal length stabilization of a tunable lens integrated focus shifting unit

Gregory Eberle; Benjamin Boesser; Konrad Wegener

doi:10.1117/12.2035104

6 March 2014 Focal length stabilization of a tunable lens integrated focus shifting unit

Gregory Eberle, Benjamin Boesser, Konrad Wegener

Proceedings Volume 8967, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX; 89670G (2014) https://doi.org/10.1117/12.2035104
Event: SPIE LASE, 2014, San Francisco, California, United States

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.

Citation Download Citation

Gregory Eberle, Benjamin Boesser, and Konrad Wegener "Focal length stabilization of a tunable lens integrated focus shifting unit", Proc. SPIE 8967, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX, 89670G (6 March 2014); https://doi.org/10.1117/12.2035104

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KEYWORDS

Laser beam diagnostics

Tunable lasers

Pulsed laser operation

Mirrors

Neodymium

Resistance

Control systems

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