Kinetic Inductance Detectors for the OLIMPO experiment: In-flight operation and performance

We report on the performance of lumped-elements Kinetic Inductance Detector (KID) arrays for mm and sub-mm wavelengths, operated at 0.3 K during the stratospheric flight of the OLIMPO payload, at an altitude of 37.8 km. We find that the detectors can be tuned in-flight, and their performance is robust against radiative background changes due to varying telescope elevation. We also find that the noise equivalent power of the detectors in flight is smaller by a factor of ~ 2, 8, 3.5, 4.5 at 150, 250, 350 and 460 GHz relative to the one measured in the laboratory, and is close to our calculated photon-noise-limited performance. The effect of primary cosmic rays crossing the detector is found to be consistent with the expected ionization energy loss with phonon-mediated energy transfer from the ionization sites to the resonators. In the OLIMPO detector arrays, at float, cosmic ray events affect less than 4% of the detector samplings for all the pixels of all the arrays, and less than 1% of the samplings for most of the pixels. These results are also representative of what one can expect from primary cosmic rays in a satellite mission with similar KIDs and instrument environment.