Laser ablated sub-wavelength structure anti-reflection coating on an alumina lens

TL;DR

This paper demonstrates the fabrication of a sub-wavelength structure anti-reflection coating on an alumina lens using laser ablation, achieving broad-band low reflectance in the millimeter-wave range, and is the first such demonstration on alumina.

Contribution

First demonstration of laser ablated sub-wavelength structure anti-reflection coating on an alumina lens with broad-band millimeter-wave transparency.

Findings

Achieved broad-band low reflectance between 110 and 290 GHz.

Measured SWS pitch of 303 μm and height of 750-790 μm.

Transmittance increased as predicted by electromagnetic simulations.

Abstract

We used laser ablation to fabricate sub-wavelength structure anti-reflection coating (SWS-ARC) on a 5 cm diameter alumina lens. With an aspect ratio of 2.5, the SWS-ARC are designed to give a broad-band low reflectance response between 110 and 290 GHz. SWS shape measurements conducted on both sides of the lens give 303 $\mu$m pitch and total height between 750 and 790 $\mu$m, matching or exceeding the aspect ratio design values. Millimeter-wave transmittance measurements in a band between 140 and 260 GHz show the increase in transmittance expected with the ARC when compared to finite element analysis electromagnetic simulations. To our knowledge, this is the first demonstration of SWS-ARC on an alumina lens, opening the path for implementing the technique for larger diameter lenses.