Injection seeding of metal-metal terahertz quantum cascade lasers

We show the coherent detection of the laser emission from seeded terahertz (THz) quantum cascade lasers (QCL) with metal-metal waveguides using free-space coupling of a THz pulses to the sub-wavelength waveguide. We implement a simple, monolithic planar horn antenna design on the metalmetal waveguide that reduces the impedance mismatch to the waveguide. The laser emission is seeded and coherently detected using electro-optic sampling. Injection seeding of metal-metal waveguides with a LO phonon depopulation design at liquid nitrogen temperatures is also demonstrated.