Low-divergence single-mode terahertz quantum cascade laser

The operation of quantum cascade lasers has to date been demonstrated over a broad frequency range in the terahertz spectrum (from 4.4 THz to 1.2 THz)(1-3). Most potential applications of terahertz quantum cascade lasers require a source that has an excellent spatial and spectral control of the radiated emission(4-7). Here, we present a distributed feedback design of a double-metal waveguide quantum cascade laser(8-10) that features a grating resonant with the third-order Bragg condition. We show that an improvement of the extraction efficiency results in control of the laser emission wavelength and enhanced output power. Moreover, the grating can act as an array of phased linear sources, reshaping the typical wide and patterned far-field of double-metal waveguides into a narrow beam of similar to 10 degrees divergence.