Integrating THz quantum cascade lasers with flexible dielectric-lined hollow metallic waveguides:Moving beyond free space optics

We demonstrate a THz optical delivery system capable of supplying a low divergence HE11 Gaussian beam at a distance of >500mm from the facet of a THz quantum cascade laser. This is achieved by optimising the optical coupling to an external hollow flexible polystyrene-lined Ag waveguide, by utilising a monolithically integrated cylindrical metal waveguide in the laser mounting block. This is shown to achieve >80% coupling efficiency between the two waveguides, whilst maintaining the spectral integrity of the laser. A comparison with other excitation geometries, such as bare laser excitation, as well as a laser with a facet coupled silicon lens, is also analysed