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Intersubband Emitters: GaAs-based Quantum-Cascade Lasers

Quantum-cascade lasers (QCLs) are semiconductor lasers that operate in the terahertz (THz) spectral region, which bridges the gap between microwave and infrared radiation (0.1–10 THz). Unlike conventional lasers, QCLs generate light through intersubband transitions within the conduction band, requiring precise engineering of GaAs/(Al,Ga)As or GaAs/AlAs heterostructures with nanometer-scale layers. Their high output power and narrow linewidth in continuous-wave operation make them excellent sources for THz spectroscopy.

In this CReA, we focus on the design, molecular beam epitaxy (MBE) growth, fabrication, and investigation of THz QCLs. Our research aims to understand the physical processes in the lasers, enhance their operating temperature, improve wall plug efficiency, and develop compact, cryogenically cooled systems. These lasers are crucial for high-resolution spectroscopy, enabling the detection of molecular rotational states, impurity transitions in semiconductors, and fine-structure transitions in atoms and ions. We also refine QCLs for use in heterodyne detectors and plasma diagnostics.

THz QCLs developed at PDI have been instrumental in astronomy and atmospheric research, such as detecting atomic oxygen in the mesosphere, as well as in future space missions and industrial applications, like measuring oxygen density in plasmas. Advancing QCL technology will expand its use in spectroscopy, imaging, and communication, unlocking new possibilities for scientific and industrial applications.

Highlights

Third-party Funded Projects

Selected Publications

2024

  1. Terahertz Quantum-Cascade Lasers: from Design to Applications
    Authors: X. Lü, B. Röben, V. Pistore, K. Biermann, E. Luna, M. Wienold, H.-W. Hübers, J. R. Wubs, J. H. van Helden, P. Gellie, and L. Schrottke
    Published in: Journal: IEEE Trans. Terahertz Sci. Technol., 14, 579 (2024)
    DOI: 10.1109/TTHZ.2024.3415501
     
  2. Performance of a high-speed pyroelectric receiver as cryogen-free detector for terahertz absorption spectroscopy measurements
    Authors: J. R. Wubs, U. Macherius, X. Lü, L. Schrottke, M. Budden, J. Kunsch, K.-D. Weltmann, J. H. van Helden
    Published in: Appl. Sci. 14, 3967 (2024)
    DOI: 10.3390/app14103967
     
  3. Phase locking of quantum-cascade lasers operating around 3.5 and 4.7 THz with a Schottky-diode harmonic mixer
    Authors: H. Richter, N. Rothbart, M. Wienold, X. Lü, K. Biermann, L. Schrottke, D. Jayasankar, J. Stake, P. Sobis, H.-W. Hübers
    Published in: Journal: IEEE Trans. Terahertz Sci. Technol., 14, 346-353 (2024)
    DOI: 10.1109/TTHZ.2024.3385379
     
  4. OSAS-B: A balloon-borne terahertz spectrometer for atomic oxygen in the upper atmosphere
    Authors: M. Wienold, A. D. Semenov, E. Dietz, S. Frohmann, P. Dern, X. Lü, L. Schrottke, K. Biermann, B. Klein, H.-W. Hübers
    Published in: IEEE Trans. Terahertz Sci. Technol., 14, 327-335 (2024)
    DOI: 10.1109/TTHZ.2024.3363135

2023

  1. Terahertz quantum-cascade lasers for high-resolution absorption spectroscopy of atoms and ions in plasmas
    Authors: X. Lü, B. Röben, K. Biermann, J. R. Wubs, U. Macherius, K.-D. Weltmann, J. H. van Helden, L. Schrottke, and H. T. Grahn
    Published in: Journal: Semicond. Sci. Technol. 38, 035003 (2023)
    DOI: 10.1088/1361-6641/acb1cd
     
  2. Terahertz absorption spectroscopy for measuring atomic oxygen densities in plasmas
    Authors: J. R. Wubs, U. Macherius, K.-D. Weltmann, X. Lü, B. Röben, K. Biermann, L. Schrottke, H. T. Grahn, and J. H. van Helden
    Published in: Plasma Sources Sci. Technol., 32, 025006 (2023)
    DOI: 10.1088/1361-6595/acb815
     
  3. Validation of THz absorption spectroscopy by a comparison with ps-TALIF measurements of atomic oxygen densities
    Authors: J. R. Wubs, L. Invernizzi, K. Gazeli, U. Macherius, X. Lü, L. Schrottke, G. Lombardi, K.-D. Weltmann, and J. H. van Helden
    Published in: Appl. Phys. Lett., 123, 081107 (2023)
    DOI: 10.1063/5.0160303
     
  4. Frequency stabilization of a terahertz quantum-cascade laser to the Lamb dip of a molecular absorption line
    Authors: R. Voigt, M. Wienold, D. Jayasankar, V. Drakinskiy, J. Stake, P. Sobis, L. Schrottke, X. Lü, H. T. Grahn, and H.-W. Hübers
    Published in: Opt. Express, 31, 13888 (2023)
    DOI: 10.1364/OE.483883

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Staff Publications