NASA applications include the use of the QCL as an LO for >2 THz receivers on the Stratospheric Observatory for Infrared Astronomy (SOFIA) as well as for future remote sensing missions. Here the narrow line width (<100 kHz) of the QCLs can be used to resolve Doppler-limited low pressure gasses (~MHz linewidth). The DFB QCL array LO would be a frequency agile, compact replacement for any gas-laser LO. The utility of this work is enhanced by the tunable range, which is expected to be ~150 GHz, allowing for a wide range of gasses to be detected with a single instrument. Applications for this technology include non-NASA-funded remote sensing instruments. Applications include gas absorption spectroscopy in fundamental research. In this application, there are currently no available frequency agile QCL sources above 2 THz with sufficient resolution to measure Doppler-limited linewidths. Long-term applications include industrial uses for trace gas detection. For industrial applications, the use of high-reliability, compact Stirling cycle coolers would greatly increase the usability of these QCL devices, which have traditionally required liquid nitrogen cooling or larger cryocooling systems.