NASA and NASA funded missions/instruments such as Aura/MLS (Microwave Limb Sounder), SOFIA/upGREAT and STO/STO-2 have demonstrated the need for local oscillator (LO) sources between 30 and 300 um (1 and 10 THz). For observations >2 THz, technologically mature microwave sources typically have microwatt power levels which are insufficient to act as LOs for a heterodyne receiver.
LongWave Photonics is proposing to develop a high power, phase/frequency-locked, single mode, THz QC-VECSEL quantum cascade laser (QC-VECSEL) system with >5 mW average power at 77K at 4.74 THz band. The system includes a THz QC-VECSEL gain chip based on metasurface gain structure with an integrated cavity adjustment structure. The VECSEL LO will be packaged in a high-reliability Stirling cycle cooler with modification to minimize vibration noise. The source will be frequency locked to a stable microwave reference with <100 kHz line width in Phase II.
NASA applications include the use of the QCL as an LO for >2 THz receivers for future missions. Here the narrow linewidth (<100 kHz) of the QC-VECSEL can be used to resolve Doppler-limited low-pressure gasses (~MHz linewidth). The QC-VECSEL LO will be a compact replacement for any gas-laser LO. The resulting source will be a compact, reliable, table-top, frequency stabilized high power THz LO with high beam quality which can sufficiently pump multi-element HEB receiver array.
Initial applications are research markets for low-pressure gas spectroscopy. The narrow line width and the ability to provide real-time frequency information of THz radiation also has great appeal. For industrial applications, the use of high-reliability, compact Stirling coolers would increase the usability of these QC-VECSEL devices, which have traditionally required liquid nitrogen cooling or larger cryocooling systems.