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Schilt, Stephane

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Schilt, Stephane
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https://libra.unine.ch/handle/123456789/492

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  • Publication
    Accès libre
    Frequency Ageing and Noise Evolution in a Distributed Feedback Quantum Cascade Laser Measured Over a Two-Month Period
    Schilt, Stephane 
    ;
    Tombez, Lionel 
    ;
    Tardy, Camille
    ;
    Bismuto, Alfredo
    ;
    Blaser, Stéphane
    ;
    Maulini, Richard
    ;
    Terazzi, Romain
    ;
    Rochat, Michel
    ;
    Südmeyer, Thomas 
    We report on the evaluation of the frequency stability of a distributed feedback quantum cascade laser (QCL) at 8 µm that was continuously monitored over a 2-month period using a spectroscopic setup. The QCL was operated in continuous wave mode at room temperature (21.4 °C). It was driven by a home-made low-noise controller at a nominal current of ∼600 mA located in the middle of its operation range. Two distinctive behaviors were observed. A monotonous frequency drift of about 1.8 GHz was observed during slightly more than the first month, followed by a stable regime in the second month where the frequency remained within a 100 MHz range. In addition, the electrical flicker noise of the QCL was regularly measured during the same period, and similarly showed two different regimes. The noise regularly decreased at a small rate of about 0.3%/day during the first month, whereas it tends to stabilize during the second month. We believe that an improvement of the QCL contacts over time is responsible for this behavior. After the initial one-month period, the QCL showed a remarkably stable behavior that is beneficial for many applications that require stable long-term operation.
  • Publication
    Accès libre
    Frequency Tuning and Modulation of a Quantum Cascade Laser with an Integrated Resistive Heater
    Gürel, Kutan
    ;
    Schilt, Stephane 
    ;
    Bismuto, Alfredo
    ;
    Bidaux, Yves
    ;
    Tardy, Camille
    ;
    Blaser, Stéphane
    ;
    Gresch, Tobias
    ;
    Südmeyer, Thomas 
    We present a detailed experimental investigation of the use of a novel actuator for frequency tuning and modulation in a quantum cascade laser (QCL) based on a resistive integrated heater (IH) placed close to the active region. This new actuator is attractive for molecular spectroscopy applications as it enables fast tuning of the QCL wavelength with a minor influence on the optical output power, and is electrically-controlled. Using a spectroscopic setup comprising a low-pressure gas cell, we measured the tuning and modulation properties of a QCL emitting at 7.8 μm as a function of the active region and IH currents. We show that a current step applied to the IH enables the laser frequency to be switched by 500 MHz in a few milliseconds, as fast as for a step of the current in the active region, and limited by heat dissipation towards the laser sub-mount. The QCL optical frequency can be modulated up to ∼100 kHz with the IH current, which is one order of magnitude slower than for the QCL current, but sufficient for many spectroscopic applications. We discuss the experimental results using a thermal model of the heat transfer in terms of cascaded low-pass filters and extract the respective cut-off frequencies. Finally, we present a proof-of-principle experiment of wavelength modulation spectroscopy of a N2O transition performed with a modulation of the IH current and show some potential benefits in comparison to QCL current modulation, which results from the reduced associated amplitude modulation.