A Frequency Selective Surface Based Focal Plane Receiver for the OLIMPO Balloon-Borne Telescope

We describe here a focal plane array of Cold-Electron Bolometer (CEB) detectors integrated in a frequency selective surface (FSS) for the 350 GHz detection band of the OLIMPO balloon-borne telescope. In our architecture, the two-terminal CEB has been integrated in the periodic unit cell of the FSS structure and is impedance matched to the embedding impedance seen by it and provides a resonant interaction with the incident submillimeter radiation. The detector array has been designed to operate in background noise limited condition for incident powers of 20 pW to 80 pW, making it possible to use the same pixel in both photometric and spectrometric configurations. We present high-frequency and dc simulations of our system, together with fabrication details. The frequency response of the FSS array, optical response measurements with hot/cold load in front of optical window, and with variable-temperature blackbody source inside cryostat are presented. A comparison of the optical response to the CEB model and estimations of noise equivalent power (NEP) is also presented.