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Author: Biermann, K. × Start date: 2020 × Has files: Yes × WGL Institute: PDI ×

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Now showing 1 - 3 of 3
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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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    Polariton-driven phonon laser
    ([London] : Nature Publishing Group UK, 2020) Chafatinos, D.L.; Kuznetsov, A. .; Anguiano, S.; Bruchhausen, A.E.; Reynoso, A.A.; Biermann, K.; Santos, P.V.; Fainstein, A.
    Efficient generation of phonons is an important ingredient for a prospective electrically-driven phonon laser. Hybrid quantum systems combining cavity quantum electrodynamics and optomechanics constitute a novel platform with potential for operation at the extremely high frequency range (30–300 GHz). We report on laser-like phonon emission in a hybrid system that optomechanically couples polariton Bose-Einstein condensates (BECs) with phonons in a semiconductor microcavity. The studied system comprises GaAs/AlAs quantum wells coupled to cavity-confined optical and vibrational modes. The non-resonant continuous wave laser excitation of a polariton BEC in an individual trap of a trap array, induces coherent mechanical self-oscillation, leading to the formation of spectral sidebands displaced by harmonics of the fundamental 20 GHz mode vibration frequency. This phonon “lasing” enhances the phonon occupation five orders of magnitude above the thermal value when tunable neighbor traps are red-shifted with respect to the pumped trap BEC emission at even harmonics of the vibration mode. These experiments, supported by a theoretical model, constitute the first demonstration of coherent cavity optomechanical phenomena with exciton polaritons, paving the way for new hybrid designs for quantum technologies, phonon lasers, and phonon-photon bidirectional translators.
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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.