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  • CLEO: Dual-Comb Spectroscopy
May 2010
SAN JOSE, Calif., May 18, 2010 — Frequency combs can improve Fourier transform spectroscopy, (FTS), according to an international team of researchers. Birgitta Bernhardt of Max Planck Institute for Quantum Optics, Germany, reported their proof-of-principle results yesterday morning at the CLEO/QELS technical session titled "Novel Sources and Systems for Spectroscopic Sensing."

Birgitta Bernhardt of the Max Planck Institute for Quantum Optics in Germany discusses MIR frequency comb Fourier transform spectroscopy on Monday, May 17, 2010, in the technical session titled "Novel Sources and Systems for Spectroscopic Sensing," part of CLEO/QELS in San Jose, Calif. Photonics Media photo by Laura S. Marshall.

There are drawbacks to traditional Fourier transform spectroscopy (FTS), Bernhardt said: the incoherent light source with its low signal-to-noise ratio (SNR); the resolution limits; the pre-determined recording time. So she and her fellow researchers set out to investigate the effects of frequency combs on FTS. Combs should improve the SNR, they reasoned, and they should improve the resolution and help to enable a more-compact setup.

They looked at the setup of a Michaelson interferometer with a moving mirror that down-converts spectra from the light source into the RF domain. Two frequency combs with slightly different repetition rates, they reasoned, should be able to replace the moving mirror.

Their proof-of-principle experiment consisted of mid-IR frequency comb Fourier transform spectroscopy, carried out with two interfering Cr2+:ZnSe femtosecond oscillators, emitting around 2400 nm. They were able to measure acetylene spectra within 10 μs with 12 GHz resolution.

The next steps, Bernhardt said, are improving the stability of the lasers used in the system; pursuing active stabilization; spectral broadening with chalcogenide PC fibers; and new sources for the infrared.

Bernhardt worked on this project with Evgeni Sorokin of Inst. fur Photonik, Technische Univ. Wien, Austria; Patrick Jacquet of Lab de Photophysique Moleculaire, CNRS, France; Raphael Thon of Lab de Photophysique Moleculaire, CNRS, France; Thomas Becker of Max-Planck-Inst. fur Quantenoptik, Germany; Irina T. Sorokina of Norwegian Univ. of Science and Technology, Norway; Theodor W. Hansch of Max-Planck-Inst. fur Quantenoptik, Germany, and Ludwig-Maximilians-Univ., Germany; and Nathalie Picque of Max-Planck-Inst. fur Quantenoptik, Germany, and Lab de Photophysique Moleculaire, CNRS, France.

Laura S. Marshall  

A smooth, highly polished surface, for reflecting light, that may be plane or curved if wanting to focus and or magnify the image formed by the mirror. The actual reflecting surface is usually a thin coating of silver or aluminum on glass.
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