4.7-THz Local Oscillator for the GREAT Heterodyne Spectrometer on SOFIA

The design and the performance of a 4.7-THz local oscillator (LO) for the GREAT (German REceiver for Astronomy at Terahertz frequencies) heterodyne spectrometer on SOFIA, the Stratospheric Observatory for Infrared Astronomy, are presented. The LO is based on a quantum-cascade laser, which is mounted in a compact mechanical cryocooler. The LO provides up to 150 μW output power into a nearly Gaussian shaped beam. It covers the frequency range from approximately +2 to -4 GHz around the fine structure line of neutral atomic oxygen, OI, at 4.7448 THz. The LO has been successfully operated on SOFIA during six observation flights in May 2014 and January 2015.