Surface emitting terahertz quantum cascade laser with a double-metal waveguide.

We investigate the implementation of surface emission via a second order grating in terahertz quantum cascade lasers with double-metal waveguides. Absorbing edge structures are designed to enforce anti-reflecting boundary conditions, which ensure distributed feedback in the cavity. The grating duty cycle is chosen in order to maximize slope efficiency. Fabricated devices demonstrate surface emission output powers that are comparable to those measured from edge-emitting double metal waveguide structures without gratings. The slope efficiency of surface emitting lasers is twice that of double-metal edge emitting structures. Surface emitting lasers show single mode behavior, with a beam divergence of approximately six degrees.