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International audience; To date no experiment has reached the level of sensitivity required to observe weak nuclear force induced parity violation (PV) energy differences in chiral molecules. In this paper, we present the approach, adopted at Laboratoire de Physique des Lasers (LPL), to measure frequency differences in the vibrational spectrum of enantiomers. We review different spectroscopic methods developed at LPL leading to the highest resolutions, as well as 20 years of CO2 laser stabilization work enabling such precise measurements. After a first attempt to observe PV vibrational frequency shifts using sub-Doppler saturated absorption spectroscopy in a cell, we are currently aiming at an experiment based on Doppler-free two-photon Ramsey interferometry on a supersonic beam. We report on our latest progress towards observing PV with chiral organo-metallic complexes containing a heavy rhenium atom.

es proprietes spectrales d'un laser femtoseconde ont ete exploitees pour realiser des mesures de frequences optiques de tres haute precision. Les mesures sont referencees a un etalon primaire situe a l'Observatoire de Paris et achemine au LPL par un lien optique. Plusieurs etalons de frequence, reposant sur des transitions electroniques ou rovibrationnelles de molecules, ont ete mesures avec des incertitudes relatives comprises entre 2x 10 -12 et 5 x 10 -14 La mesure de l'evolution de leurs frequences au cours du temps permettra de tester une eventuelle variation des constantes fondamentales.

Spectacular improvements in both resolution and signal-to-noise ratio of two-photon Ramsey fringes obtained at 30 THz have been achieved by implementing a new detection scheme. A molecular beam of SF/sub 6/, after passing through the Ramsey regions, is interrogated by a separate laser beam which makes optimal use of the entire Doppler profile by generating a comb of frequencies within a compensated high-finesse cavity. Resulting molecular spectra have the highest resolution ever obtained with CO/sub 2/ lasers and, as a standard, the system will soon outperform the best currently available.

A two-photon Ramsey-fringe experiment with a supersonic beam of SF6 has been performed with an interzone distance of up to 50 cm. Using a He-seeded beam with 50% of SF6, the two-photon transition P(4)E0 in the 2ν3 band reveals its magnetic hyperfine structure and the periodicity of the fringes is 500 Hz. The strength of the central fringe of the main hyperfine component corresponds to a flux of 1010–1011useful molecules/s, which is very promising for a new frequency standard in the 30-THz spectral region.

Nous avons pu enregistrer des signaux de franges de Ramsey a 10.6 μm sur un jet supersonique de SF 6 , avec une periode de 400 Hz et un rapport signal sur bruit de 20 dans une bande passante de 1 Hz. Les performances metrologiques atteintes par cette nouvelle source sont desormais comparables a celles de l'etalon actuel a 10.6 μm.

We report a limit on the fractional temporal variation of the proton-to-electron mass ratio as $\frac{1}{({m}_{P}/{m}_{e})}\frac{\ensuremath{\partial}}{\ensuremath{\partial}t}({m}_{P}/{m}_{e})=(\ensuremath{-}3.8\ifmmode\pm\else\textpm\fi{}5.6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}\text{ }\text{ }{\mathrm{yr}}^{\ensuremath{-}1}$, obtained by comparing the frequency of a rovibrational transition in ${\mathrm{SF}}_{6}$ with the fundamental hyperfine transition in Cs. The ${\mathrm{SF}}_{6}$ transition was accessed using a ${\mathrm{CO}}_{2}$ laser to interrogate spatial 2-photon Ramsey fringes. The atomic transition was accessed using a primary standard controlled with a Cs fountain. This result is direct and model-free.

Nous avons mis au point une nouvelle technique de mesure de frequence dans l'IR (autour de 30THz) utilisant le peigne d'un laser femtoseconde. La frequence optique est directement comparee a l'ecart entre 2 modes du laser femtoseconde, lequel depend uniquement du taux de repetition f r du laser femtoseconde. La frequence absolue de notre laser a CO 2 asservie sur une raie a deux photons de SF 6 a ete mesuree avec cette methode. Les premiers resultats montrent une deviation d'Allan de 3 × 10 -14 sur 1 s.