Quantum cascade laser progress and outlook

Recent progress and outlook in quantum cascade lasers (QCLs) in the mid- to far-infrared wavelength range (3.6-16 μm) are reviewed. Our recent work has focused on the development of high-power continuous-wave (CW) QCLs emitting in wavelengths of 4.3-6.3 μm at room temperature and above. For λ̃6 μm, advanced heterostructure geometries, including the use of a thick electroplated gold, epilayer-side heat sink lead to the first remarkable high-power CW QCL performance above room temperature, and a buried-ridge heterostructure are demonstrated to improve significantly laser performance (i.e., 579 mW at 298 K and operation up to 343 K) when combined with narrow laser ridges. Through re-engineering the optimized strain-balanced design, a similar excellent operation is achieved at 4.3-6.3 μm. The pulse operations of the shorter wavelength (3.6-4 μm) and the long wavelength (8-16 μm) QCLs at room temperature are also demonstrated. Lastly, these results are put in the perspective of other reported results and possible future directions are discussed.