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Author: Lü, X. × End date: 2024 × End date: 2023 × Start date: 2022 × DDC: 530 × Has files: Yes ×

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Now showing 1 - 5 of 5
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    Long-term stability of GaAs/AlAs terahertz quantum-cascade lasers
    (New York, NY : American Inst. of Physics, 2022) Schrottke, L.; Lü, X.; Biermann, K.; Gellie, P.; Grahn, H.T.
    We have investigated high-performance GaAs/AlAs terahertz (THz) quantum-cascade lasers (QCLs) with respect to the long-term stability of their operating parameters. The output power of lasers that contain an additional, thick AlAs refractive-index contrast layer underneath the cascade structure decreases after three months by about 35%. The deterioration of these lasers is attributed to the oxidation processes in this contrast layer starting from the facets. However, GaAs/AlAs THz QCLs with an Al0.9Ga0.1As refractive-index contrast layer exhibit long-term stability of the operating parameters over many years even when they are exposed to atmospheric conditions. Therefore, these lasers are promising high-power radiation sources in the terahertz spectral region for commercial applications.
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    Terahertz absorption spectroscopy for measuring atomic oxygen densities in plasmas
    (Bristol : IOP Publ., 2023) Wubs, J.R.; Macherius, U.; Weltmann, K.-D.; Lü, X.; Röben, B.; Biermann, K.; Schrottke, L.; Grahn, H.T.; van Helden, J.H.
    This paper describes the first implementation of terahertz (THz) quantum cascade lasers for high-resolution absorption spectroscopy on plasmas. Absolute densities of ground state atomic oxygen were directly obtained by using the fine structure transition at approximately 4.75 THz. Measurements were performed on a low-pressure capacitively coupled radio frequency oxygen discharge. The detection limit in this arrangement was found to be 2 × 10 13 cm−3, while the measurement accuracy was within 5%, as demonstrated by reference measurements of a well-defined ammonia transition. The results show that the presented method is well suited to measure atomic oxygen densities, and it closes the THz gap for quantitative atomic density measurements in harsh environments such as plasmas.
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    Terahertz quantum-cascade lasers for high-resolution absorption spectroscopy of atoms and ions in plasmas
    (Bristol : IOP Publ., 2023) Lü, X.; Röben, B.; Biermann, K.; Wubs, J.R.; Macherius, U.; Weltmann, K.-D.; van Helden, J.H.; Schrottke, L.; Grahn, H.T.
    We report on 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.
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    Terahertz quantum-cascade lasers for high-resolution absorption spectroscopy of atoms and ions in plasmas
    (Bristol : IOP Publ., 2023) Lü, X.; Röben, B.; Biermann, K.; Wubs, J.R.; Macherius, U.; Weltmann, K.-D.; van Helden, J.H.; Schrottke, L.; Grahn, H.T.
    We report on 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.
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    Terahertz quantum-cascade lasers for high-resolution absorption spectroscopy of atoms and ions in plasmas
    (Bristol : IOP Publ., 2023) Lü, X.; Röben, B.; Biermann, K.; Wubs, J.R.; Macherius, U.; Weltmann, K.-D.; van Helden, J.H.; Schrottke, L.; Grahn, H.T.
    We report on 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.