Towards a 4.75-THz local oscillator based on a terahertz quantum-cascade laser with a back-facet mirror

We report on a compact terahertz (THz) source based on a quantum-cascade laser (QCL). The source is intended for a local oscillator in a THz heterodyne receiver for the detection of the fine structure line of neutral atomic oxygen (OI) at 4.7448 THz. The QCL, which is mounted in a small mechanical cryocooler, employs a GaAs/AlAs active region heterostructure and a resonator with an additional back-facet mirror. This allows for low electrical pump powers of less than 1.2 W and high output powers of up to 8 mW. The whole setup weighs less than 4 kg. The application of such a system in a spaceborne mission appears to be feasible.