GREAT: The German first light heterodyne instrument for SOFIA

Abstract

GREAT, the German REceiver for Astronomy at Terahertz frequencies, is a first generation SOFIA dual channel heterodyne PI-instrument for high resolution spectroscopy. The system is developed by a cosortium of German research institutes. The receiver will allow simultaneous observations in two out of the following three far-infrared frequency bands: - a 1.4-1.9 THz channel for e.g. the fine-stucture line of ionized carbon [CII] at 158µm; - a 2.4-2.7 THz channel for e.g. the 112µm transition of HD; and - a 4.7 THz channel for the 63µm fine-structure line of neutral atomic oxygen. Hot electron bolometers (HEB) mixers provide state of the art sensitivity. A spectral resolving power of up to 10⁸ is achieved with chirp transform spectrometers, and a total bandwidth of 4 GHz at 1 MHz resolution is reached with wide band acousto-optical spectrometers. The modular concept of GREAT allows to observe with any combination of two out of the three channels aboard SOFIA. A more complete frequency coverage of the THz regime by adding additional GREAT channels is possible in the future. The adaptation of new LO-, mixer- or backend-techniques is easily possible. We describe details of the receiver and the results of first performance tests of the system at 1.9 THz.