Optical Breadboard Integration of a 3.5-THz Quantum-Cascade Laser Local-Oscillator for the LOCUS Atmospheric Sounder

An “elegant breadboard” system has been developed, which demonstrates the integration of terahertz-frequency (THz) sources, optics and compact cryocooler technology for the LOCUS satellite (Linking Observations of Climate, the Upper Atmosphere and Space Weather). This proposed satellite instrument has the aim of providing the first global mapping of key molecular species within the mesosphere and lower thermosphere (MLT) from low-earth orbit (LEO), using compact radiometers operating in the 0.8–4.7 THz band and a set of infrared detectors. The LOCUS THz radiometers will incorporate planar-Schottky-diode (SD) mixers, driven using waveguide-integrated local-oscillators (LOs). The LOs will be based on SD multipliers operating at 0.8 and 1.1 THz, and THz quantum-cascade lasers (QCLs) operating at 3.5 and 4.7 THz. A key technological challenge, addressed by the LOCUS elegant breadboard, is the integration of these components into a compact and robust satellite payload, including space-qualified cryocooler technology, and suitable fore-optics. In this paper, we discuss recent progress in QCL integration within the 3.5-THz channel.