Optimization of an Optical Testbed for Characterization of EXCLAIM u-Spec Integrated Spectrometers

TL;DR

This paper presents an optimized testbed setup for characterizing the spectral response of compact superconducting u-Spec spectrometers designed for the EXCLAIM far-infrared mission, enabling precise calibration and normalization.

Contribution

It introduces a novel testbed with calibration techniques for accurately measuring the spectral response of on-chip superconducting spectrometers.

Findings

Successful characterization of spectral response using a photomixer source

Implementation of on-chip reference detector for normalization

Use of silicon etalon for absolute frequency calibration

Abstract

We describe a testbed to characterize the optical response of compact superconducting on-chip spectrometers in development for the Experiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) mission. EXCLAIM is a balloonborne far-infrared experiment to probe the CO and CII emission lines in galaxies from redshift 3.5 to the present. The spectrometer, called u-Spec, comprises a diffraction grating on a silicon chip coupled to kinetic inductance detectors (KIDs) read out via a single microwave feedline. We use a prototype spectrometer for EXCLAIM to demonstrate our ability to characterize the spectrometers spectral response using a photomixer source. We utilize an on-chip reference detector to normalize relative to spectral structure from the off-chip optics and a silicon etalon to calibrate the absolute frequency.