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Three-dimensional direct laser writing via two-photon polymerization is used to fabricate anti-reflective structured surfaces (ARSSs) composed of subwavelength conicoid features optimized to operate over a wide bandwidth in the near-infrared range from 3700  cm to 6600  cm (2.7-1.52 μm). Analytic Bruggemann effective medium calculations are used to predict nominal geometric parameters such as the fill factor of the constitutive conicoid features of the anti-reflective structured surfaces (ARSSs) presented here. The performance of the ARSSs was investigated experimentally using infrared reflection and transmission measurements. An enhancement of the transmittance by 1.35%-2.14% over a broadband spectral range from 3700  cm to 6600  cm (2.7-1.52 μm) was achieved. We further report on finite-element-based reflection and transmission data using three-dimensional (3D) model geometries for comparison. A good agreement between experimental results and the finite-element-based numerical analysis is observed once as-fabricated deviations from the nominal conicoid forms are included in the model. 3D direct laser writing is demonstrated here as an efficient method for the fabrication and optimization of ARSSs designed for the infrared spectral range.

The fabrication of terahertz (THz) optics with arbitrary shapes via polymethacrylate-based stereolithography is very attractive as it may offer a rapid, lowcost avenue towards optimized THz imaging applications. In order to design such THz optical components appropriately, accurate knowledge of the complex dielectric function of the materials used for stereolithographic fabrication is crucial. In this paper we report on the complex dielectric functions of several polymethacrylates frequently used for stereolithographic fabrication. Spectroscopic ellipsometry data sets from the THz to mid-infrared spectral range were obtained from isotropically cross-linked polymethacrylate samples. The data sets were analyzed using stratified layer optical model calculations with parameterized model dielectric functions. While the infrared spectral range is dominated by a number of strong absorption features with Gaussian profiles, these materials are found to exhibit only weak absorption in the THz frequency range. In conclusion, we find that thin transmissive THz optics can be efficiently fabricated using polymethacrylate-based stereolithographic fabrication.

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