Speaker
Description
Cryogenic Single-Photon Detectors, such as Transition-Edge-Sensors (TES) and Superconducting Nanowire Single-Photon Detectors (SNSPD), have achieved high detection efficiency larger than 85\% for optical and near-infrared wavelengths. Fiber-Coupled Blackbody photons has been identified as the dominant source of background signals for both detector systems. In order the achieve ultra-low background rates while maintaining high detection efficiency an Optical Filtering System is currently in development. The system is a cryo-compatible optical U-bench, housing a ultra-narrow bandpass filter with a center wavelength of $1065\,\text{nm}$. The Cryogenic Optical Filter Bench (COFB) is mounted on the $50\,\text{K}$ stage of a dilution refrigerator, and is designed with eleven mechanical degrees of freedom (DOF), seven of which are remote-controllable and four requires manual adjustment. The seven remote-controllable DOF allows for ongoing alignment of the open optical beam through the ultra-narrowband filter to compensate for thermal contractions and the resulting transmission loses. In addition, the COFB enhances the energy-resolving capabilities of TES detectors and enables energy-selective single-photon detection for SNSPDs. We present the design, performance and current limitations of the COFB system and discuss it's applicability to ultra-low-background optical experiments, such as the rare-event search for the hypothetical axions and axion-like particles with the experiment Any Light Particle Search II (ALPS II).