Broadband near-infrared antireflection coatings fabricated by three dimensional direct laser writing

TL;DR

This paper demonstrates the fabrication of broadband near-infrared antireflection coatings using three-dimensional direct laser writing, achieving improved transmittance through optimized sub-wavelength conicoid structures validated by experiments and simulations.

Contribution

It introduces a novel application of 3D direct laser writing for creating broadband antireflective surfaces with optimized sub-wavelength features for infrared wavelengths.

Findings

Transmittance increased by up to 2.14% across the broadband range.

Good agreement between experimental measurements and finite-element simulations.

Effective medium calculations guided the design of the structured surfaces.

Abstract

Three-dimensional direct laser writing via two photon polymerization is used to fabricate anti-reflective structured surfaces composed of sub-wavelength conicoid features optimized to operate over a wide bandwidth in the near-infrared range from 3700 cm$^{-1}$ to 6600 cm$^{-1}$ (2.7 to 1.52 $\mu$m). 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 presented here. The performance of the anti-reflective structured surfaces was investigated experimentally using infrared transmission measurements. An enhancement of the transmittance by 1.35\% to 2.14\% over a broadband spectral range from 3700 cm$ ^{-1} $ to 6600 cm$^{-1}$ (2.7 to 1.52 $\mu$m) was achieved. We further report on finite-element-based reflection and transmission data using three-dimensional 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. Three-dimensional direct laser writing is demonstrated here as an efficient method for the fabrication and optimization of anti-reflective structured surfaces designed for the infrared spectral range.