Quantum cascade lasers for the 8-$\mu$m spectral range: technology, design, and analysis

Quantum cascade lasers (QCLs) have received enormous attention from the scientific community due to their broad range of applications in a wide variety of industries, agriculture, healthcare, environmental protection, and many other scientific and technical fields. In this article, in addition to a review of the main applications and the state of research and development of high-power QCLs in the mid-infrared range, we consider the features of their manufacturing technology that make it possible to obtain a high peak power and discuss the effect of overheating of the active region on the output optical power and spectral characteristics. A comparison is made of the characteristics of QCLs with the same cavity parameters but with different active regions made on the basis of substrate-matched or strained heteropairs, which provides a different energy barrier between the upper laser level and the continuum. It is shown that the use of strained heteropairs in the active region of a QCL provides an almost twofold increase in the characteristic temperature $T_0$ as well as a significantly higher efficiency and an increase in the maximum output optical power to over 21 W, which is a world record for a single stripe QCL with a $8~\mu $m spectral range.