Cold-electron bolometer with electronic microrefrigeration and general noise analysis

Abstract

A novel concept of the hot-electron bolometer using a microrefrigeration by SIN tunnel junctions for direct cooling the electrons of the absorber has been proposed. We have analyzed the most attractive case of cooling starting from 300 mK that can be achieved in a simple cryostat with <SUP>3</SUP>He pumping. Electronic cooling to 50 - 100 mK has shown considerable decrease of the electron-phonon thermal conductance G<SUB>e-ph</SUB> but small decrease of G<SUB>(Sigma</SUB> ) equals G<SUB>e-ph</SUB> + G<SUB>cool</SUB> in comparison with G<SUB>e-ph</SUB> before cooling. The maximum decrease of G<SUB>Sigma</SUB> by a factor of 1.8 has been achieved at temperatures around 200 mK. The analysis shows that the noise equivalent power (NEP) can be decreased using direct electronic cooling. The thermal noise component of NEP is decreased by a factor of 3 for electronic cooling from 300 to 100 mK mainly due to decrease of the electron temperature (and small decrease of G<SUB>(Sigma</SUB> )). Tunnel junction noise and amplifier noise components of NEP can also be improved by a factor of 4 due to increase of the power responsivity. For general noise analysis we used analytical expressions for main noise components and I-V curve of SIN tunnel junctions. The optimal bias currents were found for short noise component and amplifier noise component.