Program and Abstract Book - SRON

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19 th International Symposium on Space Terahertz Technology Invited presentation 6-1 Innovative technologies for THz heterodyne detection Thomas G. Phillips Caltech, Downs 320-47, Pasadena, CA 91106, USA The “state-of-the-art” in the field of heterodyne receivers approaches (within a factor of a few) the quantum noise limit, for frequencies up to about 700 GHz, the band-gap of niobium. Such receivers use the SIS structure and the physics of photon assisted single quasi-particle tunneling. IF bandwidths are as large as 25 GHz. Above 700 GHz various loss mechanisms set in and above about 1.4 THz HEB devices are preferred, even though the IF bandwidth is usually only a few GHz. For the future, at frequencies
19 th International Symposium on Space Terahertz Technology 6-2 2.5-THz heterodyne receiver with quantum cascade laser and hot electron bolometer mixer in a pulse tube cooler H. Richter a , H.-W. Hübers* a , S. G. Pavlov a , A. D. Semenov a , L. Mahler b , A. Tredicucci b , H. E. Beere c , D. A. Ritchie c d d , K. Il’in , M. Siegel a German Aerospace Center (DLR), Institute of Planetary Research, Rutherfordstr. 2, 12489 Berlin, Germany b NEST CNR-INFM and Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy c Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, United Kingdom d Institute of Micro- and Nano-Electronic Systems, University of Karlsruhe, 76187 Karlsruhe, Germany The terahertz (THz) portion of the electromagnetic 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 Terahertz Frequencies, which will be operated on board of SOFIA. As part of the receiver development for SOFIA we have developed a liquid cryogen-free heterodyne receiver for operation at 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 ∼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. 55
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