Quantum cascade lasers (QCLs) are semiconductor lasers based on intersubband transitions between energy states created by quantum confinement in the conduction band of semiconductor multilayers. QCLs operating in the mid-infrared region are excellent excitation sources for absorption spectroscopy, when the emission spectrum is overlapped with that of the absorption fingerprints of different molecules.

The authors of the paper demonstrated significant improvement of mid-infrared single-mode quantum cascade lasers, emitting in the wavelength range 3.8–8.3 μm, employing anti-reflection coatings in the power amplifier section. It allowed enhancing the power of the lasers up to 5 W of cw output, with wall-plug efficiency up to 16.6% at room temperature. High-power single-mode QCLs designed by the authors could have applications not only in spectroscopy but also in a wide range from defense and security to analytical, health, and environmental applications needing narrow band and high-power beams at these wavelengths.

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