Most polymeric refractive micro-optics simultaneously demand ultra-smooth 3D topographies and precise geometry for high optical performance and low stray light. We have established a surface selective smoothening for thermoplastic polymers that does not affect the designed optical geometry. For example, high curvature corners required for a 50 μm tall optical diffuser device were maintained while the surface roughness was reduced to about 10 nm RMS. 3D master structures were fabricated using direct write laser-lithography with two-photon absorption. Master structures were then replicated into poly(methyl methacrylate) through a poly(dimethyl siloxane) intermediate copying step and subsequently smoothed-out by high-energy photon exposure and thermal post-processing. The smoothening results in a lower roughness compared to a direct writing strategy using even about 50 nm vertical discretization steps still enables 10 times faster writing times.
Robert Kirchner, Nachiappan Chidambaram, Mirco Altana, and Helmut Schift, "How post-processing by selective thermal reflow can reduce the roughness of 3D lithography in micro-optical lenses," Proc. SPIE 10095, Laser 3D Manufacturing IV, 1009507 (Presented at SPIE LASE: January 30, 2017; Published: 24 February 2017); https://doi.org/10.1117/12.2258090.
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