High-resolution molecular spectroscopy in the mid-IR ­ precision measurements and tests of fundamental physics

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• Benoît Darquié (Paris - Villetaneuse)
• Friday 14 December 2012, 14:00-15:00
• Physics East 217.

If you have a question about this talk, please contact Vincent Boyer.

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Accurate molecular spectroscopy in the mid-infrared region allows precision measurements with applications in metrology or fundamental physics. I will report on some of our latest results on the determination of the Boltzmann constant kB by Doppler spectroscopy and on the search for a parity violation effect in chiral molecules. Measuring the linewidth of an isolated Doppler-broadened absorption line of ammonia around 10 µm enables a determination of kB. By fitting this lineshape to several models which include Dicke narrowing and speed-dependent collisional effects, we find that a determination of kB with an uncertainty of a few ppm is reachable. This is comparable to the current uncertainty obtained using acoustic methods and would make a significant contribution to any new value of kB determined by the CODATA . Furthermore, having multiple independent measurements at these accuracies opens the possibility of defining the kelvin by fixing kB, an exciting prospect considering the upcoming redefinition of the International System of Units. Parity violation (PV) effects have so far never been observed in chiral molecules. Originating from the weak interaction, PV should lead to frequency differences in the rovibrational spectra of the two enantiomers of a chiral molecule. However the weakness of the effect represents a very difficult experimental challenge. We propose to compare the rovibrational spectra (around 10 µm) of two enantiomers, recorded using the ultra-high resolution spectroscopy technique of Doppler-free two-photon Ramsey interferometry in a supersonic molecular beam. With an alternate beam of left- and right-handed molecules and thanks to our expertise in the control of the absolute frequency of the probe CO2 lasers, we should reach a fractional sensitivity better than 10^{-15}, on the frequency difference between enantiomers. We will review our latest results on the high-resolution spectroscopy, either in cell or in a supersonic beam, of methyltrioxorhenium, an achiral test molecule from which our collaborators are currently synthesizing chiral derivatives fulfilling all the requirements for the PV test.

This talk is part of the Cold Atoms series.

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