# Fabrication of Terahertz Fresnel Zone Plates via Ultraprecision Mechanical Processing

## TL;DR

This paper introduces a new method to fabricate high-quality terahertz Fresnel zone plates on silicon using advanced mechanical processing techniques.

## Contribution

The novel fabrication process combines ion implantation and ultra-precision diamond turning to improve silicon's ductile-to-brittle transition depth.

## Key findings

- A 3 μm amorphous layer increases the ductile-to-brittle transition depth of silicon from 55 nm to 535 nm.
- The method produces smooth microgrooves suitable for creating terahertz Fresnel zone plates with alternating transparent and opaque zones.
- Process-induced radius errors are evaluated using finite-element simulations, confirming the method's practicality for compact terahertz components.

## Abstract

This study proposes a new fabrication process for terahertz Fresnel zone plates on high-resistivity silicon substrates. It involves ion implantation surface modification, ultra-precision diamond turning, and magnetron sputtering, followed by polishing. Ductile-regime cutting is used to form smooth microgrooves, which are selectively metallized to create alternating opaque and transparent zones for terahertz waves. Finite-element simulations are performed to design the zone structure and to evaluate the effect of process-induced radius errors. A 3 μm amorphous layer is formed via ion implantation, which significantly enhances the ductile-to-brittle transition depth of silicon from 55 nm to about 535 nm while causing only minor changes in terahertz transmittance. The results demonstrate that the proposed method can produce high-quality Fresnel zone plates on silicon and offers a practical route to compact diffractive terahertz components.