Kinetic inductance detectors for the OLIMPO experiment: design and pre-flight characterization

We designed, fabricated, and characterized four arrays of horn-coupled, lumped element kinetic inductance detectors (LEKIDs), optimized to work in the spectral bands of the balloon-borne OLIMPO experiment. OLIMPO is a 2.6m aperture telescope, aimed at spectroscopic measurements of the Sunyaev-Zel'dovich (SZ) effect. OLIMPO will also validate the LEKID technology in a representative space environment. The corrected focal plane is filled with diffraction limited horn-coupled KID arrays, with 19, 37, 23, 41 active pixels respectively at 150, 250, 350, and 460 GHz.Here we report on the full electrical and optical characterization performed on these detector arrays before the flight. In a dark laboratory cryostat, we measured the resonator electrical parameters, such as the quality factors and the electrical responsivities, at a base temperature of 300 mK. The measured average resonator Qs are 1.7x10(4), 7.0x10(3), 1.0x10(4), and 1.0x10(4) for the 150, 250, 350, and 460 GHz arrays, respectively. The average electrical phase responsivities on resonance are 1.4 rad/pW, 1.5 rad/pW, 2.1 rad/pW, and 2.1 rad/pW; the electrical noise equivalent powers are 45aW/root Hz, 160aW/root Hz, 80aW/root Hz, and 140aW/root Hz, at 12 Hz. In the OLIMPO cryostat, we measured the optical properties, such as the noise equivalent temperatures (NET) and the spectral responses. The measured NET(RJ)s are 200 mu K.root s, 240 mu K.root s, 240 mu K.root s, and 340 mu K.root s, at 12 Hz; under 78, 88, 92, and 90mK Rayleigh-Jeans blackbody load changes respectively for the 150, 250, 350, and 460 GHz arrays. The spectral responses were characterized with the OLIMPO differential Fourier transform spectrometer (DFTS) up to THz frequencies, with a resolution of 1.8 GHz.