A Tunable Unidirectional Source for GUSTO’s Local Oscillator at 4.74 THz

The Galactic/Extra Ultra-Long-Duration Balloon Spectroscopic-Stratospheric Terahertz Observatory (GUSTO) is a NASA balloon-borne project and is scheduled for launch in late 2022. The balloon will carry a spectroscopic telescope that will detect three brightest emission lines from the interstellar medium. GUSTO measurements will shed light on the life cycle of the gases in the Milky Way and Large Magellanic Cloud. In this article, we will discuss the details of a quantum cascade laser used in the local oscillator for detecting the oxygen line at 4.74 THz.