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 THz emission at angles tuned by design between 0{deg} and 50{deg} was realized, leading to an original phase-matching approach, lithographically independent, for highly collimated THz QCLs.