Broadband millimeter-wave anti-reflection coatings on silicon using pyramidal sub-wavelength structures

Abstract

We used two novel approaches to produce sub-wavelength structure (SWS) anti-reflection coatings (ARC) on silicon for the millimeter and sub-millimeter (MSM) wave band: picosecond laser ablation and dicing with beveled saws. We produced pyramidal structures with both techniques. The diced sample, machined on only one side, had pitch and height of 350 µm and 972 µm. The two laser ablated samples had pitch of 180 µm and heights of 720 µm and 580 µm; only one of these samples was ablated on both sides. We present measurements of shape and optical performance as well as comparisons to the optical performance predicted using finite element analysis and rigorous coupled wave analysis. By extending the measured performance of the one-sided diced sample to the two-sided case, we demonstrate 25 % band averaged reflectance of less than 5 % over a bandwidth of 97 % centered on 170 GHz. Using the two-sided laser ablation sample, we demonstrate reflectance less than 5 % over 83 % bandwidth centered on 346 GHz.

Broadband, millimeter-wave anti-reflective structures on sapphire ablated with femto-second laser

“…To quantify the IP induced by normal incidence differential transmission we use the figure of merit 25,41…”

“…Diameters of anticipated sapphire and alumina optical elements, which are reaching 80 cm 23 , require commercially viable machining speed. To overcome these challenges we demonstrated a technique to fabricate mm-wave SWS on sapphire, alumina, and silicon using laser micro-fabrication [24][25][26][27] . With laser ablation, which has already been used in the past to ablate these and other materials [28][29][30] , there is no wear and tear of the machining tool.…”

16:1 bandwidth two-layer antireflection structure for silicon matched to the 190–310 GHz atmospheric window

“…The same group has a prototype of a five-layer structure [8] for which measurements have not been reported. Smooth-sided pyramids cut with a beveled dicing saw have been used to obtain < 5% reflectance over a 2.9:1 bandwidth [9]. In all realizations, the dicing saw approach is limited to producing AR structures that consist of crossed grooves, yielding only posts, and feature sizes are limited by practical saw blade thicknesses.…”

High efficiency terahertz generation in a multi-stage system

“…The last decades have seen a surge in research studies on generation and applications of terahertz radiation, which typically refers to electromagnetic waves in the spectral range from 0.1 to 3 THz. Among the wide range of applications, spectroscopy [1,2,3], spin dynamics control [4,5] and linear electron acceleration highly benefit from high power terahertz sources [6,7,8]. In particular, applications like particle accelerations place steep requirements of a few millijoules of single/multi-cycle terahertz pulse energy to enable bunch manipulation in the relativistic regime.…”