Terahertz quantum cascade lasers

The terahertz region (1-10 THz) of the electromagnetic spectrum offers paramount opportunities in spectroscopy, remote sensing, medical imaging and free space communications. Yet, the use of THz waves in all these fields has been limited by the lack of appropriate, convenient sources. We here report on unipolar semiconductor injection lasers that emit at THz frequencies (4.3 THz, lambda similar to 69mum and 3.5 THz, lambda similar to 85mum) and possess the potential for device-like implementation. They are based on the quantum cascade scheme employing interminiband transitions in the technologically mature AlGaAs/GaAs material system and feature a novel kind of waveguide loosely relying on the surface plasmon concept. Continuous-wave laser emission is achieved with low tresholds of a few hundred A/cm2 up to 45 K heat sink temperature and maximum output powers of more than 4 mW. Under pulsed excitation, peak output powers of 4.5 mW at low temperatures and still 1 mW at 65 K are measured. The maximum operating temperature is 67 K.