Highly sensitive far-IR KIDs for PRIMA: optical characterization of a 25-micron array

The PRobe far-Infrared Mission for Astrophysics (PRIMA) is a future cryogenic space observatory that will revolutionize study of evolving galaxies and forming planetary systems with highly-sensitive far-infrared (far-IR) imaging and spectroscopy. PRIMA’s spectrometer, the Far-InfraRed Enhanced Survey Spectrometer (FIRESS), will deploy kilo-pixel aluminum kinetic inductance detector (KID) arrays covering wavelengths from 24-235 μm. Here we present optical characterization of a prototype FIRESS array operating at 25 μm. We employ a blackbody modulation technique to measure the detector responsivity, and discuss methods for reducing 1/f noise from the multi-tone readout electronics. We measure an NEP below 3.5 × 10⁻²⁰ W/ √ Hz at 10 Hz accross the array, which exceeds the requirement to be limited by the astrophysical background limit for PRIMA’s FIRESS spectrometer. We discuss limitations of the multi-tone readout and compare results to measurements with a single-tone readout system.