2.5-THz heterodyne receiver with quantum cascade laser and hot electron bolometer mixer in a pulse tube cooler

Abstract

The terahertz (THz) portion of the elctromagnetic spectrum bears an amazing scientific potential in astronomy. High resolution spectroscopy in particular heterodyne spectroscopy of molecular rotational lines and fine structure lines of atoms or ions is a powerful tool, which allows obtaining valuable information about the observed object such as temperature and dynamical processes as well as density and distribution of particular species. Two examples are the HD rotational transition at 2.7 THz, and the OI fine structure line at 4.7 THz. These lines are main targets to be observed with GREAT, the German Receiver for Astronomy at Terahetz Frequencies, which will be operated on board of SOFIA. As part of the receiver development for about 2.5 THz. The front-end of the receiver is integrated in a pulse tube cooler (PTC). It consists of a quantum cascade laser (QCL) as local oscillator and a phonon-cooled NbN hot electron bolometric mixer. The QCL is mounted on the first stage of the PTC and operates at a temperature of about 50 K while the HEB is mounted on the second stage of the PTC (temperature about 5 K). The performance of the QCL in terms of output power, beam profile, and frequency stability as well as the noise temperature of the HEB mixer will be presented. The influence of the PTC on the receiver performance as compared to a receiver where the mixer is cooled with liquid helium will be discussed.