Silicon-based vacuum window for millimeter and submillimeter-wave astrophysics

TL;DR

This paper presents a silicon-based vacuum window with high transmittance and low reflectance for millimeter-wave astrophysics, featuring laser-ablated anti-reflection structures, successfully integrated into a telescope instrument.

Contribution

The authors designed and fabricated a novel silicon vacuum window with laser-structured anti-reflection coating, optimized for millimeter-wave astrophysical applications.

Findings

Achieved 99% transmittance and 1% reflectance across a 67% bandwidth.

Integrated the window into DESHIMA v2.0, enabling year-long astrophysical observations.

Measured optical properties agree with modeling based on sub-wavelength structures.

Abstract

We designed, fabricated, and characterized the properties of a silicon-based vacuum window suitable for millimeter-wave astrophysical applications. The window, which has a diameter of 124 mm, optically active diameter of 68 mm, and thickness of about 4 mm, gives an average transmittance and reflectance of 99% and 1%, respectively, a fractional bandwidth of 67%. Absorptive loss is below the detection limit of our measurement. The anti-reflection coating is made with laser ablated sub-wavelength structures (SWS), and the measured transmittance and reflectance values agree with modeling based on the measured SWS shapes. The window has been integrated into DESHIMA v2.0, an astrophysics instrument that took year-long observations with the Atacama Submillimeter Telescope Experiment.