Mid-infrared femtosecond frequency comb spectroscopy – COMBSPECTRO

The present project is a collaboration between the group of Dr. Nathalie Picqué at Laboratoire de Photophysique Moléculaire LPPM from CNRS (Orsay, France) and the Division of Pr. Theodor W. Hänsch at the Max Planck Institute für QuantenOptik MPQ (Garching, Germany). The project will be carried out in the frame of the European Associated Laboratory ?European Laboratory for Frequency Comb Spectroscopy? (PIs: N. Picqué, T.W. Hänsch). The methodology to be implemented is subject to a procedure of intellectual property protection. Three patents (1 CNRS, 2 CNRS-MPQ) are pending. Contacts with the company MenloSystems GmbH are also taken, for the commercial exploitation of the joint patents and results from the collaboration between LPPM and MPQ. In a first step approach, we have already shown in the frame of this collaboration that our original approach, Frequency Comb Fourier transform spectroscopy (2C-FTS), offers simultaneously large spectral bandwidth, high spectral resolution, fast acquisition time, accurate and quantitative measurements and simultaneous measurements of absorption and dispersion associated with the lines. These qualities have been demonstrated in the near-infrared region. Moreover, they reveal that a new generation of Fourier spectrometers is being designed with unprecedented qualities. The practice of Fourier transform spectroscopy may not involve any more the Michelson interferometer, which is presently the essential component of Fourier spectrometers. Based on the time domain interference of two frequency combs this new generation will benefit from the long experience of traditional FT spectroscopy. It provides an acquisition time at the limit, a potential extreme sensitivity, from low to extreme resolution, extreme accuracies, absorption and dispersion, compactness, potential spectral extension from THz to VUV. New opportunities in fields relevant to biology, chemistry, environment, industry, medicine, and physics will be provided thanks the quality of the spectra produced by this new instrumentation?Various instrumental methodologies concerned with FTS will benefit from these improvements: hyperspectral imaging, microscopy, spatial resolution, time resolution, selectivity (vibrational circular dichroism, ions, paramagnetic species, short-lived radicals?), and attenuated total reflection. The extreme sensitivity associated with the broad spectral coverage will enable the extensive spectral study of modern physical objects as for instance cold molecules or quantum solids. The applications include solid, liquid and gas states characterization, industrial process control, fundamental spectroscopy and dynamics, fundamental tests and variation of fundamental constants, rarefied samples characterization, trace gas detection (pollution, risk management), real time spectroscopy?. The objective of this project is to move to a step further in the development of 2C-FTS by reaching the molecular fingerprint mid-infrared domain. We aim at developing a cutting-edge instrument. It will outperform traditional mid-infrared Fourier transform spectroscopy by improving measurement time by a factor 100 000, sensitivity by a factor 1 000, resolution by a factor 1 000 and accuracy by a factor 100. The first one will be dedicated to low and intermediate (Doppler-limited) resolution spectroscopy and will privilege a posteriori correction of the interferogram or specific data triggering scheme (according to a patent pending), with an experimental set-up as light as possible and avoiding phase-locking electronics. This instrument will present an important commercial potential. In the course of the present project, we will focus its applications to real-time spectroscopy, time resolved spectroscopy of single events and trace gas detection, but we will also pay attention to prompt the interest of the communities that make use of spectroscopy (homeland security, chemistry, environmental monitoring, biomedicine, industrial process control?) and we will favour collaborations and disseminations of our technique both in basic research laboratories and industries. The second one will explore the potentialities of 2C-FTS for precision spectroscopy. This instrument will aim at providing unprecedented accuracies in the measurement of line profiles. We have recently shown precision in the wavenumber scale of 10 Hz (relative precision 10-13) in the 1.5 µm region. We aim at reproducing and even improving this figure in the mid-infrared, at converting this precision into an accuracy and at settling new strategies in order to make Frequency Comb Fourier transform spectroscopy an effective tool for intermediate frequency metrology. Furthermore, as the instrumental lineshape is negligible in our high resolution broadband spectra, we plan to study molecular line profiles and intensities with an extreme accuracy. We will in particular investigate the water vapour infrared continuum with this new tool.