Author
Stéphane Schilt
Other affiliations: École Polytechnique Fédérale de Lausanne
Bio: Stéphane Schilt is an academic researcher from University of Neuchâtel. The author has contributed to research in topics: Laser & Frequency comb. The author has an hindex of 27, co-authored 150 publications receiving 2508 citations. Previous affiliations of Stéphane Schilt include École Polytechnique Fédérale de Lausanne.
Papers published on a yearly basis
Papers
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TL;DR: A simple approach to this relation with an approximate formula for evaluation of the laser linewidth that can be applied to arbitrary noise spectral densities is presented.
Abstract: Frequency fluctuations of lasers cause a broadening of their line shapes. Although the relation between the frequency noise spectrum and the laser line shape has been studied extensively, no simple expression exists to evaluate the laser linewidth for frequency noise spectra that does not follow a power law. We present a simple approach to this relation with an approximate formula for evaluation of the laser linewidth that can be applied to arbitrary noise spectral densities.
520 citations
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TL;DR: A theoretical model of wavelength modulation spectroscopy that uses a laser diode on a Lorentzian absorption line and the effect of several modulation parameters on the detected signals is evaluated, confirming the relevance of the model.
Abstract: A theoretical model of wavelength modulation spectroscopy that uses a laser diode on a Lorentzian absorption line is presented. This theory describes the general case of a current-modulated semiconductor laser, for which a combined intensity and frequency modulation with an arbitrary phase shift occurs. On the basis of this model, the effect of several modulation parameters on the detected signals is evaluated. Experimental signals measured on an absorption line of CO2 by use of a 2-microm distributed-feedback laser are also presented and validate this analysis. These experimental results agree with the calculated signals, confirming the relevance of the model.
273 citations
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TL;DR: An ammonia traces analyser based on photoacoustic spectroscopy is described, which guarantees a fast response time of the system for the monitoring of ammonia, a sticky polar molecule that adheres to most surfaces.
113 citations
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TL;DR: In this paper, a theoretical description of photo-acoustic spectroscopy generated by wavelength modulation of a semiconductor laser source is reported for a Lorentzian absorption line, which describes the first and second-harmonic photoacoustic signals produced by a current-modulated semiconductor lens.
92 citations
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TL;DR: A reduction of the PA signal of almost one order of magnitude has been observed between N(2) and He, which demonstrates the importance of the buffer gas in PA spectroscopy.
84 citations
Cited by
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TL;DR: In this article, the authors present the basis for each technique, recent developments in methods and performance limitations, and present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.
Abstract: The detection and measurement of gas concentrations using the characteristic optical absorption of the gas species is important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. This study reviews the field, covering several individual gas detection techniques including non-dispersive infrared, spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy. We present the basis for each technique, recent developments in methods and performance limitations. The technology available to support this field, in terms of key components such as light sources and gas cells, has advanced rapidly in recent years and we discuss these new developments. Finally, we present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.
1,293 citations
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TL;DR: In this paper, a calibration-free wavelength-modulation spectroscopy with second harmonic detection (WMS-2f) for measurements of gas temperature and concentration in harsh environments is presented.
Abstract: We present a practical implementation of calibration-free wavelength-modulation spectroscopy with second harmonic detection (WMS-2f) for measurements of gas temperature and concentration in harsh environments. The method is applicable to measurements using lasers with synchronous wavelength and intensity modulation (such as injection current-tuned diode lasers). The key factors that enable measurements without the on-site calibration normally associated with WMS are (1) normalization of the WMS-2f signal by the first harmonic (1f) signal to account for laser intensity, and (2) the inclusion of laser-specific tuning characteristics in the spectral-absorption model that is used to compare with measured 1f-normalized, WMS-2f signals to infer gas properties. The uncertainties associated with the calibration-free WMS method are discussed, with particular emphasis on the influence of pressure and optical depth on the WMS signals. Many of these uncertainties are also applicable to calibrated WMS measurements. An example experimental setup that combines six tunable diode laser sources between 1.3 and 2.0 mum into one probe beam for measurements of temperature, H(2)O, and CO(2) is shown. A hybrid combination of wavelength and frequency demultiplexing is used to distinguish among the laser signals, and the optimal set of laser-modulation waveforms is presented. The system is demonstrated in the harsh environment of a ground-test scramjet combustor. A comparison of direct absorption and 1f-normalized, WMS-2f shows a factor of 4 increase in signal-to-noise ratio with the WMS technique for measurements of CO(2) in the supersonic flow. Multidimensional computational fluid-dynamics (CFD) calculations are compared with measurements of temperature and H(2)O using a simple method that accounts for the influence of line-of-sight (LOS) nonuniformity on the absorption measurements. The comparisons show the ability of the LOS calibration-free technique to gain useful information about multidimensional CFD models.
446 citations
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TL;DR: A review of the development, application, and current capabilities of infrared laser-absorption spectroscopy (IR-LAS) sensors for combustion gases can be found in this paper.
438 citations
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TL;DR: The most recent technological and application advances of quantum cascade lasers are reviewed, underlining the present milestones and future directions from the Mid-infrared to the Terahertz spectral range.
Abstract: We review the most recent technological and application advances of quantum cascade lasers, underlining the present milestones and future directions from the Mid-infrared to the Terahertz spectral range. Challenges and developments, which are the subject of the contributions to this focus issue, are also introduced.
406 citations