A Compact 4.75-THz Source Based on a 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 at 4.7448 THz. The laser is mounted in a mechanical cryocooler. Laser operation is realized in continuous-wave mode in the range from -2.7 to +9.4 GHz around the target frequency. Special care has been taken on the laser design, which employs a GaAs/AlAs active region heterostructure and a resonator with an additional back-facet mirror. At a typical QCL operating point (I = 200 mA, T = 60 K, ν = 4.75 THz, P
_opt
= 5 mW) close to the target frequency, this system with a mass of only 4 kg requires an electrical input power of less than 130 W for a cooling capacity of up to 4 W. The maximum optical output power of the QCL reaches up to 8 mW with an electrical pump power of less than 1.8 W. The application of such a system in a spaceborne mission appears to be feasible.