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Author: Hübers, H.-W. × DDC: 620 × WGL Institute: PDI ×

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Now showing 1 - 3 of 3
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    A compact, continuous-wave terahertz source based on a quantum-cascade laser and a miniature cryocooler
    (Washington, DC : Optical Society of America, 2010) Richter, H.; Greiner-Bär, M.; Pavlov, S.G.; Semenov, A.D.; Wienold, M.; Schrottke, L.; Giehler, M.; Hey, R.; Grahn, H.T.; Hübers, H.-W.
    We report on the development of a compact, easy-to-use terahertz radiation source, which combines a quantum-cascade laser (QCL) operating at 3.1 THz with a compact, low-input-power Stirling cooler. The QCL, which is based on a two-miniband design, has been developed for high output and low electrical pump power. The amount of generated heat complies with the nominal cooling capacity of the Stirling cooler of 7 W at 65 K with 240 W of electrical input power. Special care has been taken to achieve a good thermal coupling between the QCL and the cold finger of the cooler. The whole system weighs less than 15 kg including the cooler and power supplies. The maximum output power is 8 mW at 3.1 THz. With an appropriate optical beam shaping, the emission profile of the laser is fundamental Gaussian. The applicability of the system is demonstrated by imaging and molecular-spectroscopy experiments.
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    Frequency modulation spectroscopy with a THz quantum-cascade laser
    (Washington, DC : Optical Society of America, 2013) Eichholz, R.; Richter, H.; Wienold, M.; Schrottke, L.; Hey, R.; Grahn, H.T.; Hübers, H.-W.
    We report on a terahertz spectrometer for high-resolution molecular spectroscopy based on a quantum-cascade laser. High-frequency modulation (up to 50 MHz) of the laser driving current produces a simultaneous modulation of the frequency and amplitude of the laser output. The modulation generates sidebands, which are symmetrically positioned with respect to the laser carrier frequency. The molecular transition is probed by scanning the sidebands across it. In this way, the absorption and the dispersion caused by the molecular transition are measured. The signals are modeled by taking into account the simultaneous modulation of the frequency and amplitude of the laser emission. This allows for the determination of the strength of the frequency as well as amplitude modulation of the laser and of molecular parameters such as pressure broadening.
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    Doppler-free spectroscopy with a terahertz quantum-cascade laser
    (Washington, DC : Optical Society of America, 2018) Wienold, M.; Alam, T.; Schrottke, L.; Grahn, H.T.; Hübers, H.-W.
    We report on the Doppler-free saturation spectroscopy of a molecular transition at 3.3 THz based on a quantum-cascade laser and an absorption cell in a collinear pump-probe configuration. A Lamb dip with a sub-Doppler linewidth of 170 kHz is observed for a rotational transition of HDO. We found that a certain level of external optical feedback is tolerable as long as the free spectral range of the external cavity is large compared to the width of the absorption line.