THz surface emission by difference frequency generation in quantum cascade lasers

We present THz surface emission by difference frequency generation in nonlinear quantum cascade lasers operating at room temperature. The device comprises two separate, transversely superimposed gratings, one for selective feedback of the mid-infrared modes and one for surface emission of the generated THz radiation. The mid-infrared grating is realized as a higher order, loss-coupled distributed feedback grating for single mode emission at two distinct wavelengths. It defines the spatial distribution of the nonlinear polarization wave, which allows for precise placement of the second order top grating for surface emission.