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Hofstetter, Daniel

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

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  • 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
    Room temperature, continuous wave operation of distributed feedback quantum cascade lasers with widely spaced operation frequencies
    (2006)
    Wittmann, Andreas
    ;
    Giovannini, Marcella 
    ;
    Faist, Jérôme
    ;
    Hvozdara, Lubos
    ;
    Blaser, Stéphane
    ;
    Hofstetter, Daniel 
    ;
    Gini Emilio
    Lasing properties of room temperature, continuous wave operated distributed feedback (DFB) quantum cascade lasers are reported. A bound-to-continuum active region was used to generate a broad gain spectrum. As a result, first-order DFB lasers employing different periods allowed us to achieve single mode continuous wave emission at several wavelengths ranging from 7.7 to 8.3 µm at a temperature of +30 °C. The frequency span corresponds to 8% of the center frequency.
  • 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
    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
    Bound-to-continuum and two-phonon resonance, quantum-cascade lasers for high duty cycle, high-temperature operation
    (2002)
    Faist, Jérôme
    ;
    Hofstetter, Daniel 
    ;
    Beck, Mattias
    ;
    Aellen, Thierry
    ;
    Rochat, Michel
    ;
    Blaser, Stéphane
    Recent advances in quantum-cascade (QC) laser active-region design are reviewed. Based on a rate equation model of the active region, we show why new gain regions. based on a two-phonon resonance or a bound-to-continuum transition exhibit significantly better performance than the traditional design based on a three-quantum-well active region. Threshold current densities as low as 3 kA/cm2 at T = 300 K, operation with a peak power of 90 mW at 425 K, single-mode high-power operation up to temperatures above 330 K at λ ≈ 16 μm and continuous wave operation up to T = 311 K are demonstrated. QC lasers able to operate at high duty cycles (50%) on a Peltier cooler were used in a demonstration of a 300-MHz free-space optical link between two buildings separated by 350 m.
  • Publication
    Accès libre
    Terahertz intersubband emission in strong magnetic fields
    (2002)
    Blaser, Stéphane
    ;
    Rochat, Michel
    ;
    Beck, Mattias
    ;
    Hofstetter, Daniel 
    ;
    Faist, Jérôme
    Electroluminescence in quantum-cascade structures based on vertical transitions is studied in a strong perpendicular magnetic field in the limit in which the cyclotron energy is larger than the intersubband transition energy. Cyclotron emission and a luminescence intensity enhancement up to a factor of 6 is observed in GaAs/AlGaAs and InGaAs/InAlAs vertical transition-based quantum-cascade structures.
  • Publication
    Accès libre
    Free-space optical data link using Peltier-cooled quantum cascade laser
    (2001)
    Blaser, Stéphane
    ;
    Hofstetter, Daniel 
    ;
    Beck, Mattias
    ;
    Faist, Jérôme
    The authors demonstrate a free-space optical data link over 350 m using a Peltier-cooled 9.3 µm quantum cascade laser operating at a duty cycle of almost 50%. On the emitter side, a Ge lens was used for beam collimation and a flat mirror for beam steering, while on the receiver side, a fast room-temperature HgCdTe detector in combination with a Φ = 16 cm mirror telescope detected the incoming signal. Short pulses at a maximum repetition rate of 330 MHz were successfully transmitted. The signal-to-noise ratio of the measurement was limited by the power equivalent noise of the detector.