A 1-THz superconducting hot-electron-bolometer receiver for astronomical observations

In this paper, we describe a superconducting hot-electron-bolometer mixer receiver developed to operate in atmospheric windows between 800-1300 GHz. The receiver uses a waveguide mixer element made of 3-4-nm-thick NbN film deposited over crystalline quartz. This mixer yields double-sideband receiver noise temperatures of 1000 K at around 1.0 THz, and 1600 K at 1.26 THz, at an IF of 3.0 GHz. The receiver was successfully tested in the laboratory using a gas cell as a spectral line test source. It is now in use on the Smithsonian Astrophysical Observatory terahertz test telescope in northern Chile.

I. Introduction

Spectral LINE emission from numerous important atoms and molecules, including water, carbon, carbon monoxide (CO), and nitrogen can be observed in the terahertz frequency region, especially between 0.3–2.5 THz [1]. Nevertheless, the universe is largely unexplored between 1–5 THz because the Earth's atmosphere is almost completely opaque. Recent atmospheric measurements, however, have confirmed that several windows can open up between 1–3 THz at very high dry locations [2], [3]. Furthermore, three windows, centered at 1.03, 1.35, and 1.5 THz, show transmission as high as 40% under favorable conditions. These windows contain a number of rotational transitions of carbon monoxide, an abundant tracer of cool molecular gas in the galaxy, along with the ground state transition of singly ionized atomic nitrogen, and numerous other common and exotic molecular species. Immediate interest now exists in the scientific community to perform heterodyne observations at terahertz frequencies from the ground, along with observations from air- and space-borne platforms currently under development.