High-Power Mid-Infrared Quantum Cascade Semiconductor Lasers

Quantum cascade lasers (QCLs) employ intersubband transitions between conduction-band (CB) energy states in multi-quantum-well (MQW) structures, carrier tunneling between adjacent MQW stages, and coherent-light emission from multiple (30–50) stages. Unlike interband-transition semiconductor lasers, QCLs are not affected by Auger recombination in the mid-infrared wavelength range (λ= 3–20 μm); thus, allowing them to readily reach lasing at room temperature (RT). However, using multiple stages leads to high voltages (≥ 10 V) that significantly decrease the wallplug efficiency, ηwp. Thus, although pulsed RT operation was obtained in 1996, it took until 2002 to achieve CW RT operation and until 2008 to obtain 1 W CW power.1