Development of THz Coherent Sources Using Quantum Cascade Lasers

We are developing quantum cascade lasers (QCLs) and superconductive hot- electron bolometer (HEB) mixers for a THz heterodyne receiver system. We have successfully fabricated QCLs which can be operated in a continuous oscillation mode at the frequency around 3.1THz. The QCLs are made of a GaAs/Al0:15Ga0:85As material system using a resonant LO phonon scattering depopulation scheme, and are processed in a metal-metal waveguide with the size of 40"m wide and 1.5mm long by using gold-gold thermo compression wafer bonding tech- nique and a dry-etching method. We have also succeeded in operating the quasi-optical HEB mixer at 3.1THz by using the fabricated QCL as a local oscillator source. We report the cur- rent status of our developments, demonstrating possibilities of THz-QCLs for heterodyne sensing applications in various research flelds.