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Hofstetter, Daniel

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Hofstetter, Daniel
Affiliation principale
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Ancien.ne collaborateur.trice
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https://libra.unine.ch/handle/123456789/472

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  • Publication
    Accès libre
    Microfluidic tuning of distributed feedback quantum cascade lasers
    (2006)
    Diehl, Laurent
    ;
    Lee, Benjamin G.
    ;
    Behroozi, Peter
    ;
    Loncar, Marko
    ;
    Belkin, Mikhail
    ;
    Capasso, Federico
    ;
    Aellen, Thierry
    ;
    Hofstetter, Daniel 
    ;
    Beck, Mattias
    ;
    Faist, Jérôme
    In this Letter, we report the tuning of the emission wavelength of a single mode distributed feedback quantum cascade laser by modifying the mode effective refractive index using fluids. A fabrication procedure to encapsulate the devices in polymers for microfluidic delivery is also presented. The integration of microfluidics with semiconductor laser (optofluidics) is promising for new compact and portable lab-on-a-chip applications.
  • Publication
    Accès libre
    23 GHz operation of a room temperature photovoltaic quantum cascade detector at 5.35 µm
    (2006)
    Hofstetter, Daniel 
    ;
    Graf, Marcel
    ;
    Aellen, Thierry
    ;
    Faist, Jérôme
    ;
    Hvozdara, Lubos
    ;
    Blaser, Stéphane
    We present a room temperature operated 5.35 µm quantum cascade detector which was tested at high frequencies using an optical heterodyne experiment. Two slightly detuned continuous wave distributed feedback single mode quantum cascade lasers were used to generate a beating signal. The maximum frequency at which the resulting microwave signal could be detected was 23 GHz. The cutoff behavior of our device was modeled with a simple RLC circuit and showed excellent agreement with the experimental data.
  • Publication
    Accès libre
    Spectroscopic study of the ν1 band of SO2 using a continuous-wave DFB QCL at 9.1 µm
    (2004)
    Joly, L.
    ;
    Zéninari, V.
    ;
    Parvitte, B.
    ;
    Weidmann, D.
    ;
    Courtois, D.
    ;
    Bonetti, Yargo
    ;
    Aellen, Thierry
    ;
    Beck, Mattias
    ;
    Faist, Jérôme
    ;
    Hofstetter, Daniel 
    We report results of spectroscopic measurements with a continuous-wave distributed-feedback quantum-cascade laser (DFB QCL). Line intensities and self-broadening coefficients were measured in the ν1 band of SO2 between 1088 and 1090 cm-1. The self-broadening coefficients in this paper confirm the typical decrease of νself with increasing rotational quantum number K’’a. The line intensities determined here are smaller than those in the HITRAN 2000 database. Several lines found in this study were not present in the database.
  • Publication
    Accès libre
    Mid-infrared trace-gas sensing with a quasi- continuous-wave Peltier-cooled distributed feedback quantum cascade laser
    (2004)
    Weidmann, D.
    ;
    Tittel, F. K.
    ;
    Aellen, Thierry
    ;
    Beck, Mattias
    ;
    Hofstetter, Daniel 
    ;
    Faist, Jérôme
    ;
    Blaser, Stéphane
    A recently developed distributed feedback quantum cascade laser (QCL) capable of thermoelectric-cooled (TEC) continuous-wave (cw) operation and emitting at ~9 μm is used to perform laser chemical sensing by tunable infrared spectroscopy. A quasi-continuous-wave mode of operation relying on long current pulses (~5 Hz, ~50% duty cycle) is utilized rather than pure cw operation in order to extend the continuous frequency tuning range of the quantum cascade laser. Sulfur dioxide and ammonia were selected as convenient target molecules to evaluate the performance of the cw TEC QCL based sensor. Direct absorption spectroscopy and wavelength-modulation spectroscopy were performed to demonstrate chemical sensing applications with this novel type of quantum cascade laser. For ammonia detection, a 18-ppm noise-equivalent sensitivity (1 σ) was achieved for a 1-m absorption path length and a 25-ms data-acquisition time using direct absorption spectroscopy. The use of second-harmonic-detection wavelength-modulation spectroscopy instead of direct absorption increased the sensitivity by a factor of three, achieving a normalized noise-equivalent sensitivity of 82 ppbHz-1/2 for a 1-m absorption path length, which corresponds to 2×10-7 cm-1Hz-1/2.
  • Publication
    Accès libre
    Continuous-wave operation of quantum cascade laser emitting near 5.6 µm
    (2003)
    Yarekha, D. A.
    ;
    Beck, Mattias
    ;
    Blaser, Stéphane
    ;
    Aellen, Thierry
    ;
    Gini Emilio
    ;
    Hofstetter, Daniel 
    ;
    Faist, Jérôme
    Buried heterostructure quantum cascade lasers emitting at 5.64 µm are presented. Continuous-wave (CW) operation has been achieved at –30°C for junction down mounted devices with both facets coated. A 750 µm-long laser exhibited 3 mW of CW power with a threshold current density of 5.4 kA/cm2.
  • Publication
    Accès libre
    Continuous wave operation of quantum cascade lasers
    (2003)
    Beck, Mattias
    ;
    Hofstetter, Daniel 
    ;
    Aellen, Thierry
    ;
    Blaser, Stéphane
    ;
    Faist, Jérôme
    ;
    Oesterle, Ursula
    ;
    Gini Emilio
    Continuous wave (CW) operation of quantum cascade lasers is reported up to temperatures of 312 K. The devices were fabricated as buried heterostructure lasers and episide-down mounted for improved heat dissipation. Fabry–Perot lasers emitted 17 mW of continuous optical power at 292 K and still 3 mW at 311 K at λ=9.12 μm. Distributed feedback quantum cascade lasers showed CW single-mode operation up to 260 K at λ=9.0 μm with a side mode suppression rate better than 30 dB.
  • Publication
    Accès libre
    Free-running 9.1-μm distributed-feedback quantum cascade laser linewidth measurement by heterodyning with a C18O2 laser
    (2003)
    Weidmann, D.
    ;
    Joly, L.
    ;
    Parpillon, V.
    ;
    Courtois, D.
    ;
    Bonetti, Yargo
    ;
    Aellen, Thierry
    ;
    Beck, Mattias
    ;
    Faist, Jérôme
    ;
    Hofstetter, Daniel 
    We report spectral linewidth measurements of a 9.1-μm distributed-feedback quantum cascade laser (QCL). The free-running QCL beam was mixed with a waveguide isotopic C18O2 laser onto a high-speed HgCdTe photomixer, and beat notes were recorded from a radio-frequency spectral analyzer. Beating was performed at two operating conditions, first near the QCL laser threshold (beating with the C18O2R10 line) and then at a high injection current (beating with the C18O2R8 line). Overall, beat note widths of 1.3–6.5 MHz were observed, which proves that a free-running QCL can have a short-term spectral width near 1 MHz.
  • Publication
    Accès libre
    High-frequency modulation of a quantum-cascade laser using a monolithically integrated intracavity modulator
    (2003)
    Hofstetter, Daniel 
    ;
    Beck, Mattias
    ;
    Aellen, Thierry
    ;
    Blaser, Stéphane
    We report a quantum-cascade laser monolithically integrated with an intracavity modulator which could be operated up to 1 GHz. In contrast to earlier approaches, where the radio frequency (RF) modulation signal was supplied to the entire cavity length of the laser structure, we drive only a relatively small 375-/spl mu/m-long section of the cavity. At the same time, a quasi-continuous-wave signal was supplied to the remaining 1125-/spl mu/m-long section. This modulation scheme resulted in smaller parasitic capacitance effects than what we reported previously, and enabled us to work with lower RF voltages and currents.
  • Publication
    Accès libre
    Continuous-wave distributed-feedback quantum-cascade lasers on a Peltier cooler
    (2003)
    Aellen, Thierry
    ;
    Blaser, Stéphane
    ;
    Beck, Mattias
    ;
    Hofstetter, Daniel 
    ;
    Faist, Jérôme
    ;
    Gini Emilio
    Continuous-wave operation of λ~9 µm distributed-feedback quantum-cascade lasers is reported up to a temperature of 260 K. Single-frequency emission with a side mode suppression ratio of ≥27 dB and with a tuning range of 5 cm–1 between 200 and 245 K (a tunability of –0.078 cm–1/K and –0.764 cm–1/W) is obtained for the junction-down mounted buried heterostructure devices. Uncoated lasers display an output power of up to 18 mW at 180 K and still 1 mW at 250 K. Lasers with high-reflection coated facets could be operated up to 260 K.
  • Publication
    Accès libre
    Distributed-feedback quantum cascade lasers emitting in the 9-μm band with InP top cladding layers
    (2002)
    Hofstetter, Daniel 
    ;
    Beck, Mattias
    ;
    Aellen, Thierry
    ;
    Faist, Jérôme
    ;
    Oesterle, Ursula
    ;
    Ilegems, Marc
    ;
    Gini Emilio
    ;
    Melchior, Hans
    Two different high performance quantum cascade distributed-feedback lasers with four quantum-well-based active regions and InP top cladding layers are presented. The first device, which emitted at 9.5 μm, was mounted junction down in order to get high average powers of up to 71 mW at -30°C and 30 mW at room temperature. The other device, which lased at 9.1 μm, was optimized for high pulsed operating temperatures and tested up to 150°C at 1.5% duty cycle. The emission of both lasers stayed single mode with more than 20-dB side-mode suppression ratio over the entire investigated power and temperature range.