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 mu m and 9.7 mu m, and produce single-mode THz output at similar to 2.9 THz with a side mode suppression ratio of similar to 25 dB. A high mid-infrared to THz conversion efficiency of 0.8 mW/W-2 is obtained at room temperature.