Terahertz Quantum-Cascade Lasers: From Design to Applications

• Published in: IEEE transactions on terahertz science and technology Vol. 14; no. 5; pp. 579 - 591
• Main Authors: Lu, Xiang, Roben, Benjamin, Pistore, Valentino, Biermann, Klaus, Luna, Esperanza, Wienold, Martin, Hubers, Heinz-Wilhelm, Wubs, Jente R., van Helden, Jean-Pierre H., Gellie, Pierre, Schrottke, Lutz
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 01.09.2024; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Active regions (lasers); Aluminum arsenides; Atomic oxygen; Continuous radiation; Cryogenic cooling; Fabry-Perot interferometers; Fourier transforms; Gallium arsenide; Heterostructures; High-resolution spectroscopy; Laser transitions; Lasers; Optical waveguides; Quantum cascade lasers; quantum-cascade laser (QCL); Single mode operation; Spectrometers; Spectroscopy; terahertz (THz) spectroscopy; Terahertz communications; Terahertz frequencies; Terahertz radiation; Thickness; Waveguide lasers; Waveguides
• ISSN: 2156-342X; 2156-3446
• DOI: 10.1109/TTHZ.2024.3415501

We report on the development and the application of high-performance terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/Al<inline-formula><tex-math notation="LaTeX">_{x}</tex-math></inline-formula>Ga<inline-formula><tex-math notation="LaTeX">_{1-x}</tex-math></inline-formula>As heterostructures. These lasers with emission frequencies between 2.6 and 4.7 THz are based on a hybrid design, which is preferred for continuous-wave applications. For the design of the active regions, we employ an efficient Fourier-transform-based model, which also allows for the simulation of heterostructures with gradual interfaces. Since the inherent interface width is on the same order as the thickness of the layers in the active region, the use of nominally binary AlAs barriers results in an effective Al content up to <inline-formula><tex-math notation="LaTeX">x</tex-math></inline-formula> <inline-formula><tex-math notation="LaTeX">=</tex-math></inline-formula> 0.6 for the tallest barriers. For practical applications, Fabry-Pérot lasers based on single-plasmon waveguides are fabricated. Single-mode operation is in most cases achieved by using short cavities. In particular, GaAs/AlAs THz QCLs show a sufficiently high wall plug efficiency so that they can be operated in miniature mechanical cryocoolers. Currently, high-performance THz QCLs are used for commercial continuous-wave, table-top THz systems, local oscillators in 3.5- and 4.7-THz heterodyne spectrometers, and absorption spectrometers for the determination of the density of atomic oxygen in plasmas.