Alignment and optical verification of DESHIMA 2.0 at ASTE

TL;DR

This paper presents an alignment and verification procedure for the DESHIMA 2.0 spectrometer, improving its aperture efficiency at the ASTE telescope through a novel sky chopper and hexapod beam scanning method.

Contribution

The paper introduces a new alignment procedure using a sky chopper and hexapod to optimize the optical coupling of DESHIMA 2.0 at ASTE, validated through laboratory and on-site tests.

Findings

Alignment procedure significantly improved aperture efficiency.

Beam coupling to cold sky was successfully achieved.

Verification confirmed the effectiveness of the alignment method.

Abstract

We developed, characterized, and verified an alignment procedure for the DESHIMA 2.0 instrument, an ultra wide-band spectrometer operating between 200--400 GHz, at the ASTE telescope. To this end, we mounted the warm optics, consisting of a modified Dragonian dual reflector system, on a motor controlled hexapod. Crucial in the alignment procedure is our sky chopper, which allows fast beam switching. It has a small entrance and exit aperture coupling to (cold) sky, which creates a measurable signal with respect to the warm cabin environment. By scanning the instrument beam across the entrance aperture of the sky chopper using the hexapod, we found the hexapod configuration that produced the lowest signal on our detectors, implying the beam is coupled fully to cold sky and not the warm cabin. We first characterized the alignment procedure in the laboratory, where we used a vat containing liquid nitrogen as the cold source behind the sky chopper. Then, we applied the alignment procedure to DESHIMA 2.0 at ASTE. We found that the alignment procedure significantly improved the aperture efficiency compared to previously reported values of the aperture efficiency of DESHIMA at ASTE, which indicates the veracity of the alignment procedure.