GREAT: the SOFIA high-frequency heterodyne instrument

TL;DR

GREAT is a modular, high-frequency heterodyne instrument for SOFIA, enabling high-resolution far-infrared spectroscopy with excellent in-flight performance and ongoing technological improvements.

Contribution

This paper details the design, construction, and successful in-flight operation of GREAT, a novel modular heterodyne instrument for high-frequency FIR astronomy on SOFIA.

Findings

Achieved diffraction-limited optics with nominal efficiencies.

Demonstrated state-of-the-art receiver sensitivities.

Successfully performed multiple science flights since 2011.

Abstract

We describe the design and construction of GREAT, the German REceiver for Astronomy at Terahertz frequencies operated on the Stratospheric Observatory for Infrared Astronomy (SOFIA). GREAT is a modular dual-color heterodyne instrument for highresolution far-infrared (FIR) spectroscopy. Selected for SOFIA's Early Science demonstration, the instrument has successfully performed three Short and more than a dozen Basic Science flights since first light was recorded on its April 1, 2011 commissioning flight. We report on the in-flight performance and operation of the receiver that - in various flight configurations, with three different detector channels - observed in several science-defined frequency windows between 1.25 and 2.5 THz. The receiver optics was verified to be diffraction-limited as designed, with nominal efficiencies; receiver sensitivities are state-of-the-art, with excellent system stability. The modular design allows for the continuous integration of latest technologies; we briefly discuss additional channels under development and ongoing improvements for Cycle 1 observations. GREAT is a principal investigator instrument, developed by a consortium of four German research institutes, available to the SOFIA users on a collaborative basis.