Advances in Terahertz Quantum-Cascade Lasers for Real-World Applications
/ Announcements
The invited paper, Terahertz Quantum-Cascade Lasers: From Design to Applications, authored by PDI scientists Xiang Lü, Benjamin Röben, Valentino Pistore, Klaus Biermann, Esperanza Luna, and Lutz Schrottke, was recently published in the IEEE Transactions on Terahertz Science and Technology’s Special Issue, Selected Emerging Trends in Terahertz Science and Technology, and selected as a Feature Paper. This work represents a collaboration between PDI and researchers from the Institute of Optical Sensor Systems of the German Aerospace Center (DLR, Berlin), the Leibniz Institute for Plasma Science and Technology (INP, Greifswald), and Lytid SAS (Orsay, France). The paper provides an overview of the design, fabrication, and practical application of advanced terahertz (THz) quantum-cascade lasers (QCLs), with a particular focus on high-resolution terahertz spectroscopy. PDI has a strong track record in developing and providing THz QCLs for real-world applications.
The lasers featured in this study enable continuous-wave operation in mechanical coolers, with output powers reaching up to 10 mW. Recently, lasers emitting below 3 THz have also been developed. When integrated into Lytid’s commercial table-top terahertz systems, these lasers serve as versatile radiation sources for the 2.5 to 4.8 THz spectral range.
QCLs are unrivaled radiation sources for terahertz high-resolution spectroscopy, which relies on fine-structure and rotational transitions in atoms and molecules. For instance, the 3P1 → 3P2 fine-structure transition in neutral atomic oxygen (OI) emits and absorbs electromagnetic radiation with a rest frequency of 4.744777 THz, while the 1F5/2 → 1F7/2 rotational transition of the hydroxyl radical (OH) occurs at 3.551192 THz. Lasers with appropriate frequencies and tuning ranges developed by PDI have been successfully integrated into heterodyne and absorption spectrometers by our partners at DLR and INP, respectively.
A recent DLR instrument utilizing a QCL local oscillator is OSAS-B, a heterodyne receiver designed to observe the 4.75-THz emission from atomic oxygen in the mesosphere and lower thermosphere. In this system, the laser operates at a liquid/solid nitrogen-cooled stage. Due to water absorption in the troposphere, observations are conducted from a stratospheric balloon gondola. The measured spectra exhibit a distinctive wing structure, stemming from absorption and emission interactions in atmospheric layers with significant temperature gradients.
At INP, researchers have demonstrated precise measurements of atomic oxygen densities in plasma environments by detecting the atomic oxygen fine-structure transition in a capacitively-coupled radio-frequency oxygen plasma. THz absorption spectroscopy was benchmarked against a more established yet complex and costly method—two-photon absorption laser-induced fluorescence—with highly consistent results. This validation underscores the potential of QCL-based absorption spectroscopy in practical applications, particularly in the microelectronics industry.
Publication
Title: Terahertz Quantum-Cascade Lasers: From Design to Applications
Authors: Xiang Lü, Benjamin Röben, Valentino Pistore, Klaus Biermann, Esperanza Luna, Martin Wienold, Heinz-Wilhelm Hübers, Jente R. Wubs, Jean-Pierre H. van Helden, Pierre Gellie, and Lutz Schrottke
DOI: 10.1109/TTHZ.2024.3415501
Scientific Contact
Dr. Xiang Lü, Paul-Drude-Institut fur Festkörperelektronik, Leibniz Institut im Forschungsverbund Berlin e.V., Hausvogteiplatz 5-7, 10117 Berlin, Germany.
Email: lue@pdi-berlin.de