Efficient terahertz-wave generation in mid-infrared quantum-cascade lasers with a common dual-upper-state active region

We report the performance of room temperature, single mode terahertz sources based on intracavity difference frequency generation in mid-infrared quantum cascade lasers with a common dual-upper-state (DAU) active region. As a result of designing of DAU active region for giant optical nonlinearity, the DAU devices with a dual-period buried distributed feedback grating operate in two single-mode mid-infrared wavelengths at 10.7 um and 9.7 um, and produce single-mode THz output at ~2.9 THz with a side mode suppression ratio of ~25 dB. A high mid-infrared to THz conversion efficiency of 0.8 mW/W is obtained at room temperature.