01-Dec-2009 - Ludwig-Maximilians-Universität München (LMU)

Instantaneous trace gas fingerprint with laser frequency combs

Scientists at the MPQ record ultrasensitive absorption broadband spectra within tens of microseconds by combining cavity enhancement and frequency comb spectroscopy

Trace gas spectroscopic detection has drawn much interest in recent years, as it both allows a better understanding of the molecular spectra of weak overtone transitions and in situ non-intrusive sensing of compounds at low concentration. However, recording a broadband spectrum within a very short measurement time and with high sensitivity remains a challenge. At the Max Planck Institute of Quantum Optics, a team of scientists around Professor Theodor W. Hänsch and Doctor Nathalie Picqué in a cooperation involving the Laboratoire de Photophysique Moléculaire du Centre National de la Recherche Scientifique (Orsay, France), the University of Tokyo (Chiba, Japan) and the Ludwig Maximilian's University (Munich, Germany) have implemented a new instrument, based on laser frequency combs, which holds much promise for such a breakthrough. The remarkable convergence between two separate fields, ultrafast optics and frequency metrology, has led to the precise control of the frequency spectrum produced by mode-locked lasers, which consists of a regular comb of sharp lines. The resulting optical frequency combs, pioneered by 2005 Nobel Prize laureate Professor Theodor W. Hänsch, have had tremendous impact on the various areas of precision measurement and extreme nonlinear optics. A growing list of applications includes molecular spectroscopy. Here, the new instrument comes into play. All the equidistant modes of a first laser frequency comb are injected into a resonant passive high finesse cavity, which contains a gas sample. Inside the cavity the interaction length between the light and the sample is dramatically enlarged due to multiple reflections. This enhances the molecular absorption signal by several orders of magnitude. The light transmitted by the cavity exhibits a broad band spectrum of absorption lines, which needs to be analysed by a spectrometer: a second frequency comb, with a slightly detuned repetition frequency. The beat notes between pairs of lines from the two combs reveal the optical spectrum. This Fourier transform spectrometer without moving parts is one-million times faster than the scanning Michelson-based Fourier transform interferometer, which has been the dominating instrument in analytical sciences for decades. The cavity-enhanced dual-comb spectrometer described here has the potential to become a powerful tool for ultrasensitive spectroscopy without sacrificing high-resolution, spectral bandwidth, and high-speed. A proof-of-principle experiment has been undertaken by Birgitta Bernhardt, with the help of Akira Ozawa and Patrick Jacquet, all graduate students. With Ytterbium-based fiber frequency combs emitting around 1040 nm, they succeeded for the first time in resolving the crowded weak overtone spectrum of ammonia, a molecule of planetological and environmental interests. Moreover the spectrum was recorded within only 18 microseconds and the achieved sensitivity is already 20-fold better, with a 100-fold shorter measurement time, than present state-of-the-art experiments. "As we are able to record such sensitive spectra every 20 microseconds, our technique exhibits an intriguing potential for the monitoring of chemical reactions or the spectroscopic sensing of dynamic single-events. Furthermore, we could extend our experimental concept to any region of the electromagnetic spectrum, in particular to the mid-infrared 'molecular fingerprint' region where no powerful real-time techniques are available at present. Here the implementation of the cavity-enhanced-dual-comb method would for instance allow sub-ppb minimum detectable concentrations for a variety of molecules of atmospheric relevance. This exhilarating perspective however still presents challenging issues", states Birgitta Bernhardt. The field of trace gas sensing is presently advancing in many different directions ranging from biomedicine to environmental monitoring or analytical chemistry, plasma physics and laboratory astrophysics. The cavity-enhanced dual-comb spectroscopy technique might find many important applications for practical spectroscopy. Original publication: B. Bernhardt et al.; "Cavity-enhanced dual-comb spectroscopy"; Nature Photonics, Advance Online Publication, January 2010

Ludwig-Maximilians-Universität München (LMU)

Request information now

Recommend news PDF version / Print

Share on

Facts, background information, dossiers
  • láser
  • ytterbium
  • plasma
  • ammonia
More about LMU
More about Max-Planck-Gesellschaft
More about University of Tokyo
  • News

    Electrons Passed Around

    Photoinduced charge transfers are an interesting electronic property of Prussian blue and some analogously structured compounds. A team of researchers has now been able to elucidate the ultrafast processes in the light-induced charge transfer between iron and manganese in a manganese-contai ... more

    How does your computer smell?

    A keen sense of smell is a powerful ability shared by many organisms. However, it has proven difficult to replicate by artificial means. Researchers combined biological and engineered elements to create what is known as a biohybrid component. Their volatile organic compound sensor can effec ... more

    World’s first fingertip-mounted sensor that maintains user’s sensitivity

    Scientists from the Technical University of Munich (TUM) and the University of Tokyo have developed an ultrathin pressure sensor that can be attached directly to the skin. It can measure how fingers interact with objects to produce valuable data for technological or medical applications. Th ... more

More about Centre National de la Recherche Scientifique
  • News

    A protein that makes you do the twist

    Asymmetry plays a major role in biology at every scale: think of DNA spirals, the fact that the human heart is positioned on the left, our preference to use our left or right hand ... A team from the Institute of biology Valrose (CNRS/Inserm/Université Côte d'Azur), in collaboration with co ... more

    For a Better Contrast

    Magnetic resonance imaging (MRI) has emerged as one of the most powerful clinical imaging tools because of its superb spatial resolution and soft tissue contrast, especially when using contrast agents. In the European Journal of Inorganic Chemistry, scientists have presented a new kind of n ... more

    Olivier Voinnet awarded 2009 EMBO Gold Medal

    Olivier Voinnet from the CNRS Institute of Plant Molecular Biology in Strasbourg, France, is awarded the 2009 EMBO Gold Medal. The researcher receives this medal for his pioneering work on the mechanisms and roles of gene silencing via RNA in plants. With this annual award, the European Mo ... more

More about MPI für Quantenoptik
  • News

    Innovative Blood Test Based on Infrared Light

    A new study carried out by a team of laser physicists, molecular biologists and physicians based at LMU Munich and the Max Planck Institute for Quantum Optics has confirmed the temporal stability of the molecular composition of blood in a population of healthy individuals. The data provide ... more

    The next phase of the proton puzzle

    Scientists at the Max Planck Institute of Quantum Optics (MPQ) have succeeded in testing quantum electrodynamics with unprecedented accuracy to 13 decimal places. The new measurement is almost twice as accurate as all previous hydrogen measurements combined and moves science one step closer ... more

    Laser takes pictures of electrons in crystals

    Microscopes of visible light allow us to see tiny objects such living cells and their interior. Yet, they cannot discern how electrons are distributed among atoms in solids. Now researchers around Prof. Eleftherios Goulielmakis of the Extreme Photonics Labs at the University of Rostock and ... more