Noise temperature and beam pattern of an NbN hot electron bolometer mixer at 5.25 THz

Abstract

We report the measured sensitivities of a superconducting NbN hot electron bolometer ͑HEB͒ heterodyne receiver at 5.25 THz. Terahertz ͑THz͒ radiation is quasioptically coupled to a HEB mixer with a lens and a spiral antenna. Using a measurement setup with black body calibration sources and a beam splitter in vacuo, and an antireflection coated Si lens, we obtained a double sideband ͑DSB͒ receiver noise temperature ͑T rec DSB ͒ of 1150 K, which is nine times h / 2k, where h is the Planck constant, the frequency, and k the Boltzmann constant. In addition, the measured far field beam patterns of the integrated lens antenna show nearly collimated beams from 2.5 to 5.3 THz that allow reliable measurement of T rec DSB using the vacuum setup. Our experimental results in combination with an antenna-to-bolometer coupling simulation suggest that the HEB mixer can work well at least up to 6 THz, making it suitable for next generation of high-resolution spectroscopic space telescopes and, in particular, for the detection of the neutral atomic oxygen line at 4.7 THz.

A 4.7THz heterodyne receiver for a balloon borne telescope

“…For heterodyne mixing at 4.7 THz, we use a single pixel HEB in a quasi-optical configuration. The HEB is a 2 x 0.2 μm 2 superconducting NbN bridge coupled to a tight wound spiral antenna that is shown to give excellent response at super-THz frequencies up to at least 5.3 THz [9]. THz radiation is coupled into the HEB antenna using a 10 mm diameter Si elliptical lens, which is AR coated for ~ 25 % improved transmission.…”

Low noise terahertz MgB2 hot-electron bolometer mixers with an 11 GHz bandwidth

“…3 Despite the apparent advantage over SIS, HEB mixers show an excellent noise performance in a rather limited IF band: the 3 dB noise bandwidth (NBW) of NbN HEB mixers (currently, the most frequently used HEB mixers) is not more than 4-5 GHz. [4][5][6] The IF range >5 GHz becomes unusable.…”

Development of superconducting mixers for THz astronomy

“…In addition, we have also participated in the efforts of Netherland Institute for Space Research (SRON) and Delft University of Technology (TUDelft) on the development of superconducting HEB mixers around 5 THz and the integration of THz superconducting HEB mixers with THz quantum cascade lasers (QCLs). The measured noise performances are all summarized in Figure 2 [27][28][29][30][31][32]. Note that low frequency results were measured earlier with no specific optimization of the measurement setup.…”