Benchmarking surface selective vacuum ultraviolet and thermal postprocessing of thermoplastics for ultrasmooth 3-D-printed micro-optics

Robert Kirchner; Nachiappan Chidambaram; Helmut Schift

doi:10.1117/1.OE.57.4.041403

6 January 2018 Benchmarking surface selective vacuum ultraviolet and thermal postprocessing of thermoplastics for ultrasmooth 3-D-printed micro-optics

Robert Kirchner, Nachiappan Chidambaram, Helmut Schift

Author Affiliations +

Funded by: Swiss Nanoscience Insitute

Optical Engineering, Vol. 57, Issue 4, 041403 (January 2018). https://doi.org/10.1117/1.OE.57.4.041403

Abstract

State-of-the-art, polymeric, refractive micro-optics simultaneously require an ultrasmooth three-dimensional (3-D) surface and a precise geometry for excellent optical performance with minimal stray light. In earlier work, we have established a surface finishing process for thermoplastic polymer master structures that is only effective on the surface and does not affect the designed optical geometry, thus enabling polishing without touching. Therewith, the high curvature corners of a 50-μm-tall optical diffuser device were maintained while the surface roughness was reduced to about 10-nm root mean square. For this, 3-D master structures were first fabricated by direct write laser-lithography with two-photon polymerization. The master structures were replicated into poly(methyl methacrylate) through a poly(dimethyl siloxane) intermediate replication stamp. Finally, all structures were surface-polished by selective high-energy photon exposure and thermal postprocessing. In this work, we focus on the comparison of the surface smoothening using either postprocessing or dedicated direct writing strategies. For this comparison, strategies for modifying the exposed voxel size and the writing discretization being the primary source of roughness were tested by sweeping the laser exposure dose for two different resist materials and objectives. In conclusion, the postprocessing smoothening resulted in a lower roughness compared to a direct writing strategy—even when 50-nm vertical discretization steps were used—and still enabled 10 times shorter writing times.

Citation Download Citation

Robert Kirchner, Nachiappan Chidambaram, and Helmut Schift "Benchmarking surface selective vacuum ultraviolet and thermal postprocessing of thermoplastics for ultrasmooth 3-D-printed micro-optics," Optical Engineering 57(4), 041403 (6 January 2018). https://doi.org/10.1117/1.OE.57.4.041403

Received: 21 July 2017; Accepted: 13 November 2017; Published: 6 January 2018

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