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High-resolution QCL frequency comb spectrometer for the detection of trace gases and their isotopes

English title High-resolution QCL frequency comb spectrometer for the detection of trace gases and their isotopes
Applicant Emmenegger Lukas
Number 176584
Funding scheme Bridge - Discovery
Research institution Luftfremdstoffe / Umwelttechnik EMPA
Institution of higher education Swiss Federal Laboratories for Materials Science and Technology - EMPA
Main discipline Other disciplines of Physics
Start/End 01.05.2018 - 30.04.2022
Approved amount 2'000'000.00
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All Disciplines (3)

Other disciplines of Physics
Climatology. Atmospherical Chemistry, Aeronomy
Microelectronics. Optoelectronics

Keywords (4)

Heterodyne Spectroscopy; Frequency Comb; Trace Gas Analysis; Quantum Cascade Lasers

Lay Summary (German)

Der mittlere Infrarotbereich (MIR) des elektromagnetischen Spektrums enthält die fundamentalen Rotations-Schwingungsübergänge der meisten gasförmigen Moleküle. Diese Eigenschaft ist relevant für unzählige analytische Anwendungen in den Bereichen Umwelt, Medizin, Industrie und Sicherheit. Infrarot Frequenzkämme basierend auf Quantenkaskadenlasern (QCL) haben das Potential, die Gasanalytik, durch eine bisher unerreichte Kombination von Präzision, Geschwindigkeit und spektraler Abdeckung, zu revolutionieren.
Lay summary
Inhalt und Ziele

Im Projekt CombTrace werden neuartige QCL-Frequenzkämme entwickelt, die eine hohe optische Bandbreite aufweisen und das gesamte MIR Spektrum abdecken (ETHZ, J. Faist). Entscheiden ist dabei die Kompaktheit, Helligkeit, und optische Leistungsdichte dieser Halbleiter-Laser. Durch spezielle Frequenz-Locking-Techniken werden die QCL Frequenzkämme so stabilisiert, dass eine bisher unerreichte Empfindlichkeit in spektroskopischen Anwendungen möglich wird (UniNE, T. Südmeyer). Der optische Aufbau in einem Heterodynespektrometer erlaubt die spektral hochaufgelöste Analytik von gasförmigen Molekülen und deren Isotope, zum beispiel des Radiocarbons 14CO2 (Empa, L. Emmenegger). In Zusammenarbeit mit dem Industriepartner (IRSweep) wird ein Demonstrator für die zeitlich und spektral hochaufgelöste Analytik von Spurengasen und deren Isotope entwickelt.


Die Heterodynespektroskopie mit Halbleiterlasern im mittleren Infrarotbereich eröffnet grundlegend neue Möglichkeiten in der Spurengasanalytik. Da keine mechanischen Teile verwendet werden, ergibt sich das Potential für miniaturisierte Designs. Dies hohe Empfindlichkeit und Selektivität ist für zahlreiche Anwendungen in den Bereichen Umwelt, Medizin, Sicherheit und Industrie von grosser Bedeutung.
Direct link to Lay Summary Last update: 12.02.2018

Responsible applicant and co-applicants


Associated projects

Number Title Start Funding scheme
145138 Laser spectroscopic breath analysis for the prevention of obesity through indi-vidual energy balance monitoring 01.01.2014 NRP 69 Healthy Nutrition and Sustainable Food Production
166104 Spectral properties of quantum cascade lasers: from noise analysis to stabilization 01.04.2016 Project funding (Div. I-III)
148992 ICOS-CH: Integrated Carbon Observation System in Switzerland 01.07.2013 Research Infrastructure
165639 Monolithic, self referenced quantum cascade laser frequency comb 01.04.2016 Project funding (Div. I-III)
157208 Balloon-borne mid-infrared laser spectroscopy for in-situ water vapor measurements in the Upper Troposphere and Lower Stratosphere 01.02.2015 Project funding (Div. I-III)
166255 Clumped isotopes as a novel tracer for the N2O cycle 01.09.2016 Project funding (Div. I-III)


The mid-infrared (MIR) part of the electromagnetic spectrum contains the fundamental ro-vibrational transitions of a wide range of molecules that are relevant in environmental, medical, industrial and security applications. Quantum Cascade Lasers (QCLs) are arguably the most attractive MIR light source for spectroscopy. Switzerland plays a leading role both in the development of QCLs, pioneered by the co-applicant J. Faist, and in their application in laser spectroscopy. The group of the main applicant L. Emmenegger at Empa is a major player in this field, in particular for the challenging measurement of isotopic ratios. Recently, J. Faist’s group at ETHZ has demonstrated the first direct MIR frequency comb generation from QCLs, thus paving the ground for MIR combs that uniquely combine compactness, brightness, speed, and spectral coverage. This development has the potential for revolutionizing dual-comb heterodyne spectroscopy in the MIR, which is rapidly gaining interest as it has the combined potential of high accuracy and precision with wide spectral coverage and fast acquisition.To date, however, QCL comb spectroscopy is still strongly limited by the spectral stability, coverage, and resolution of QCL combs. Consequently, suitable applications are mainly those requiring fast spectral analysis of liquids and solids, which have inherently broad and strong absorption features. CombTrace will bring fundamental change by providing a large spectral coverage of > 200 cm-1 with a resolution in the kHz range and a sub-MHz spectral sampling rate. These properties will be made possible by integrating another scientific field of strong Swiss expertise, which is time and frequency metrology in the laboratory of co-applicant T. Südmeyer. This will lead to unprecedented sensitivity, selectivity, and multicomponent capability in gas spectroscopy, as will be demonstrated by the measurement of the rare radiocarbon (14CO2) and the simultaneous detection of several multiply substituted (clumped) isotopologues of carbon dioxide. Both are highly relevant in environmental and medical applications, and provide an excellent demonstrator for countless future applications.To achieve these goals, CombTrace proposes to develop the next generation of QCL combs that exhibit high optical bandwidth, even in the most challenging 4-5 um spectral range, and of fundamental redesigns to provide dispersion compensation at high power operation. Furthermore, specific locking techniques will be developed to stabilize QCL combs to allow high resolution and sensitivity in spectroscopic measurements. The optical setup will be designed to achieve outstanding signal-to-noise ratio, and it will include temperature-controlled multipass absorption cells that allow adjusting the population of the ro-vibrational states (hot-bands) of the target molecules to increase the selectivity for selected (isotopic) species. Furthermore, specific quantification algorithms will be developed to fully benefit from both the large spectral coverage and high resolution offered by QCL combs. In short, CombTrace relies on the following work-packages led by highly experienced and recognized partners:(i)development of QCL combs at 4-5 um with high optical power and large bandwidth(J. Faist, ETHZ);(ii)stabilization of QCL frequency combs with respect to power and frequency by locking techniques(T. Südmeyer, UniNE);(iii)development of QCL dual-comb demonstrator for selected trace gases, including 14CO2 and multiply substituted CO2 isotopologues (L. Emmenegger, Empa).The strong involvement of the implementation partner IRsweep - an ETH and Empa spin-off company - guarantees that the consortium remains focused on developments that are relevant for future commercial applications and technology transfer. Furthermore, it acknowledges the fact that dual QCL combs have the potential to achieve miniaturized designs that may open the door to large volume markets.