We have demonstrated waveguide integration of terahertz quantum cascade
lasers (THz QCLs) at frequencies above 4.7 THz. A precision
micromachining technique, followed by diamond-turning and
electroless-plating has been used to manufacture hollow rectangular
waveguides with integrated diagonal feedhorns. We show that surface
roughness at the 1μm level is achieved, enabling outcoupling of
radiation in the 4.75–5.05 THz band, with a divergence angle of 5°
along the plane of the QCL substrate.