2023
- 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
- 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
- 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
- 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
- Terahertz quantum-cascade lasers for high-resolution absorption spectroscopy of atoms and ions in plasmas
This CReA has developed terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures, which exhibit single-mode emission at 3.360, 3.921, and 4.745 THz. These frequencies are in close correspondence to fine-structure transitions of Al atoms, N+ ions, and O atoms, respectively. Due to the low electrical pump power of these THz QCLs, they can be operated in a mechanical cryocooler in continuous-wave mode, while a sufficient intrinsic tuning range of more than 5 GHz is maintained. The single-mode operation and the intrinsic tuning range of these THz QCLs allow for the application of these lasers as radiation sources for high-resolution absorption spectroscopy to determine the absolute densities of Al atoms, N+ ions, and O atoms in plasmas.
- Correlation between emission frequency and location on the wafer for terahertz quantum-cascade lasers
The correlation between the emission frequency and the location on the wafer due to an inhomogeneous growth rate across the wafer was investigated for GaAs/AlAs terahertz (THz) quantum-cascade lasers (QCLs) using experiments and simulations. For several wafers, we observe a blue shift of the emission frequency from the center to the edge of the wafer. This blue shift is attributed to a decrease of the thickness of the QCL, which can be determined with spectroscopic techniques. The correlation of the calculated frequencies with the actual emission frequencies of QCLs fabricated from different locations on the wafer allows to establish an effective method for the fabrication of THz QCLs emitting at a particular target frequency.
- High-performance GaAs/AlAs terahertz quantum-cascade lasers for spectroscopic applications
Terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures have been developed for application-defined emission frequencies between 3.4 and 5.0 THz. These THz QCLs can be used as local oscillators in airborne or satellite-based astronomical instruments or as radiation sources for high-resolution absorption spectroscopy. The GaAs/AlAs THz QCLs can be operated in mechanical cryocoolers and even in miniature mechanical cryocoolers due to their comparatively high wall-plug efficiency of around 0.2% and typical current densities below 500 A/cm2. These lasers exhibit output powers of more than 1 mW at operating temperatures up to about 70 K, which is sufficient for most of the abovementioned applications.