Sensitivity of a hot electron bolometer heterodyne receiver at 4.3 THz

摘要

We have studied the sensitivity of a superconducting NbN hot electron bolometer mixer integrated with a spiral antennaat 4.3 THz. Using hot/cold blackbody loads and a beam splitter all in vacuum, we measured a double sideband receivernoise temperature of 1300 K at the optimum local oscillator (LO) power of 330 nW, which is about 12 times thequantum noise (hv /2k_B).Our result indicates that there is no sign of degradation the mixing process at super-THzfrequencies. Also, a measurement method is introduced where the hot/cold response of the receiver is recorded atconstant voltage bias of the mixer, while varying the LO power. We argue that this method provides an accuratemeasurement of the receiver noise temperature, which is not influenced by the LO power fluctuations and the directdetection effect. Moreover, our sensitivity data suggests that one can achieve a receiver noise temperature of 1420 K atthe frequency of [OI] line (4.7 THz), which is scaled from the sensitivity at 4.3 THz with frequency.