Optical Characterization & Testbed Development for {\mu}-Spec Integrated Spectrometers

TL;DR

This paper details the development of a cryogenic optical testbed for characterizing u-Spec integrated spectrometers, including initial validation with prototypes and plans for testing higher-resolution devices for a space mission.

Contribution

It introduces a new optical characterization testbed for u-Spec spectrometers and demonstrates initial validation with prototype devices, enabling future high-resolution device testing.

Findings

Successful initial optical measurements of R=64 devices

Validation of the testbed with prototype devices

Outline of test plan for R=512 devices

Abstract

This paper describes a cryogenic optical testbed developed to characterize u-Spec spectrometers in a dedicated dilution refrigerator (DR) system. u-Spec is a far-infrared integrated spectrometer that is an analog to a Rowland-type grating spectrometer. It employs a single-crystal silicon substrate with niobium microstrip lines and aluminum kinetic inductance detectors (KIDs). Current designs with a resolution of 512 are in fabrication for the EXCLAIM (Experiment for Cryogenic Large Aperture Intensity Mapping) balloon mission. The primary spectrometer performance and design parameters are efficiency, NEP, inter-channel isolation, spectral resolution, and frequency response for each channel. Here we present the development and design of an optical characterization facility and preliminary validation of that facility with earlier prototype R=64 devices. We have conducted and describe initial optical measurements of R = 64 devices using a swept photomixer line source. We also discuss the test plan for optical characterization of the EXCLAIM R = 512 u-Spec devices in this new testbed.