Optical characterization of 150 GHz polarimetric thermal kinetic inductance detector arrays

Precise measurements of the polarization of the cosmic microwave background (CMB) require detector architectures capable of scaling to large arrays. Thermal kinetic inductance detectors (TKIDs) offer a promising path toward this scaling; however, previous validations have been limited to small prototype chips. Here, we present a comprehensive optical characterization of full arrays of antenna-coupled TKIDs designed for CMB polarimetry at 150 GHz. These arrays are optimized for the expected sky loading of ≈20K. To characterize these resonators under the high optical loads typical of laboratory environments (≈300K), we implemented a “fast chirp” pulsed readout technique. Beyond this specific application, fast chirp readout can be readily applied to extract information from any array of under-coupled resonators with broad resonances. We report system optical efficiencies in excess of 30%, Gaussian antenna beam patterns that match simulations, and spectral bands that fill the targeted 150 GHz atmospheric window with a 25% bandwidth. Furthermore, we constrain the stimulation of absorbers by stray radiation bypassing the antenna to negligible levels. These results validate the optical performance of full-scale TKID arrays, demonstrating their viability for next-generation CMB experiments.