Cold-Electron Bolometers with SQUID Readout for OLIMPO Balloon Telescope

The OLIMPO experiment is a 2.6 m balloon-borne telescope, aimed at measuring the Sunyaev-Zeldovich effect in clusters of Galaxies. OLIMPO will carry out surveys in four frequency bands centered at 140, 220, 410 and 540 GHz. The detector system consists of four bolometer arrays and incorporates new detector technologies that are potential candidates for future space missions. One of these technologies is the Capacitively Coupled Cold-Electron Bolometer (CEB) with SQUID readout. The SQUID readout has been already developed for TES bolometers with typical sensitivity of 1 pA/Hz1/2. The goal is to achieve noise-equivalent power (NEP) of the CEB with standard SQUID readout (without additional transformer) less than photon noise. The CEB is a planar antenna-coupled superconducting detector with high sensitivity and high dynamic range. To achieve noise matching with SQUID for the estimated in-flight optical power load, a parallel array of Cold-Electron Bolometers has to be used. This array can be easy realized in proposed arrangement of OLIMPO receiving system with four coplanar lines for each channel. Two CEBs can be inserted in each coplanar line and combined in parallel would give eight parallel CEBs for each channel. To increase efficiency of CEB for current readout, an optimal configuration of CEB with capacitively coupled SIN junction and Andreev SN contact has been used. In this configuration the strong electron cooling and currnt response for incoming signal are realized by one single junction. The volume of normal metal is partly squeezed due to proximity effect of a superconducting electrode from the Andreev contact that increase efficiency of the electron cooling. Simulations show that photon noise level can be achieved at 300 mK for the parallel array of eight CEBs for all frequency ranges with the estimated in-flight optical power load for OLIMPO