Distributed feedback terahertz frequency quantum cascade lasers with dual periodicity gratings

We have developed terahertz frequency quantum cascade lasers that exploit a double-periodicity distributed feedback grating to control the emission frequency and the output beam direction independently. The spatial refractive index modulation of the gratings necessary to provide optical feedback at a fixed frequency, and simultaneously, a far-field emission pattern centered at controlled angles, was designed through use of an appropriate wavevector scattering model. Single mode terahertz (THz) emission at angles tuned by design between 0 degrees and 50 degrees was realized, leading to an original phase-matching approach for highly collimated THz quantum cascade lasers.