In 1983, at the time of the adoption of the present definition of the metre by the 17th General Conference on Weights and Measures (CGPM), the International Committee for Weights and Measures (CIPM) drew up recommendations for the practical realization of the definition. These have formerly been referred to as the mise en pratique of the definition of the metre. It was understood that the practical realization would, from time to time, be updated to take account of new measurements and improvements in techniques of laser stabilization. In 1992 the CIPM, acting on the advice of the then Consultative Committee for the Definition of the Metre (CCDM), adopted a revision of the mise en pratique in its Recommendation 3 (CI-1992). The text was published in Metrologia (1993/94 30 523–41). In 1997 a second revised version of the practical realization of the definition of the metre was adopted by the CIPM in its Recommendation 1 (CI-1997). The text was published in Metrologia (1999 36 211–44). In 2001, the CIPM again adopted a revised version of the practical realization of the metre and this time included recommended frequencies for other optical frequency standards. The text of this Recommendation (Recommendation 1 (CI-2002)) is given here∗. In addition, a revised list of recommended radiations, and an appendix containing the source data used in estimating the wavelengths, frequencies and uncertainties of the recommended radiations are given. In adopting the revised practical realization, the CIPM acknowledged the considerable effort put into its preparation by the Consultative Committee for Length (CCL) through its Working Group on the mise en

https://iopscience.iop.org/article/10.1088/0026-1394/40/2/316/pdf

Practical realization of the definition of the metre, including recommended radiations of other optical frequency standards (2001)

Three distinct techniques exist for distributing an ultrastable frequency reference over optical fibers. For the distribution of a microwave frequency reference, an amplitude-modulated continuous wave (cw) laser can be used. Over kilometer-scale lengths this approach provides an instability at 1 s of ∼3×10−14 without stabilization of the fiber-induced noise and ∼1×10−14 with active noise cancellation. An optical frequency reference can be transferred by directly transmitting a stabilized cw laser over fiber and then disseminated to other optical and microwave regions using an optical frequency comb. This provides an instability at 1 s of 2×10−14 without active noise cancellation and 3×10−15 with active noise cancellation [Recent results reduce the instability at 1 s to 6×10−18.] Finally, microwave and optical frequency references can be simultaneously transmitted using an optical frequency comb, and we expect the optical transfer to be similar in performance to the cw optical frequency transfer. The insta...

Remote transfer of ultrastable frequency references via fiber networks

Parity violation leads to energy differences ΔpvH=NAΔpvE of enantiomers in the femtojoule to picojoule per mole range. Recently introduced methods of electroweak quantum chemistry predict such energy differences to be one to two orders of magnitude larger than previously accepted—but still very small. How can such small energies be measured and what are the consequences for our understanding of molecular chirality, biomolecular homochirality, and perhaps fundamental physics? The review gives some tentative answers to these questions. We discuss the current status of theory and some of the current experimental approaches.

How Important is Parity Violation for Molecular and Biomolecular Chirality

We give a snapshot of the rapidly developing field of ultracold polar molecules and walk the reader through the papers appearing in this Topical Issue.

https://link.springer.com/content/pdf/10.1140%2Fepjd%2Fe2004-00151-x.pdf

Editorial: Quo vadis, cold molecules?

We present theoretical predictions and experimental measurements for the achievable phase noise, timing jitter, and frequency stability in the coherent transport of an optical frequency over a fiber-optic link. Both technical and fundamental limitations to the coherent transfer are discussed. Measurements of the coherent transfer of an optical carrier over links ranging from 38 to 251 km demonstrate good agreement with theory. With appropriate experimental design and bidirectional transfer on a single optical fiber, the frequency instability at short times can reach the fundamental limit imposed by delay-unsuppressed phase noise from the fiber link, yielding a frequency instability that scales as link length to the 3/2 power. For two-way transfer on separate outgoing and return fibers, the instability is severely limited by differential fiber noise.

High-stability transfer of an optical frequency over long fiber-optic links

We have developed a saturation spectroscopy experiment to test the prediction that enantiomers of chiral molecules have different spectra because of the parity violation associated with neutral currents in the weak interaction between electrons and nuclei. First experimental tests have been conducted on hyperfine components of vibration-rotation transitions of CHFClBr in the $9.3\ensuremath{\mu}\mathrm{m}$ spectral range. The frequencies of saturation resonances of separated enantiomers have been compared and found to be identical within 13 Hz ( $\ensuremath{\Delta}\ensuremath{\nu}/\ensuremath{\nu}l{4.10}^{\ensuremath{-}13}$).

Limit on the parity nonconserving energy difference between the enantiomers of a chiral molecule by laser spectroscopy

We present in this article results on a new dissemination system of an ultrastable reference signal at 100 MHz on a standard fiber network. The 100 MHz signal is simply transferred by amplitude modulation of an optical carrier. Two different approaches for compensating the noise introduced by the link have been implemented. The limits of the two systems are analyzed and several solutions are suggested in order to improve the frequency stability and to further extend the distribution distance. Nevertheless, our system is a good tool for the best cold atom fountains comparison between laboratories, up to 100 km, with a relative frequency resolution of 10 −14 at 1 s integration time and 10 −17 for 1 day of measurement. The distribution system may be upgraded to fulfill the stringent distribution requirements for the future optical clocks.

/pdf/high-resolution-frequency-standard-dissemination-via-optical-5ci58nqke0.pdf

High resolution frequency standard dissemination via optical fiber metropolitan network

We have developed a frequency stabilization scheme for CO/sub 2/ lasers using only external modulation via an electrooptic modulator (EOM). One of the two laser sidebands which are generated by the EOM and frequency-modulated is set in resonance with a Fabry-Perot cavity, itself filled with OsO/sub 4/ as an absorber. The saturation signal of an OsO/sub 4/ line detected in transmission of the Fabry-Perot cavity is used for stabilization. We obtained a stability of 0.1 Hz (/spl Delta//spl nu///spl nu/=3.5 10/sup -15/) on a 100-s time scale, and a reproducibility up to 10 Hz with the strongest OsO/sub 4/ reference lines. These results largely improve the performance of our previous setup for which modulation was applied through piezoelectric transducers. Further, the stabilized laser is not frequency-modulated and is easily tunable.

CO/sub 2/ laser stabilization to 0.1-Hz level using external electrooptic modulation

We have stabilized a CO2 laser on narrow saturated absorption resonances of CO2 detected on the transmitted beam of an external Fabry-Perot cavity in the 30 THz spectral region. By using another CO2 laser stabilized on a close OsO4 line whose absolute frequency is precisely known, and measuring the beat frequency 4 with a precision of 100 Hz, we determined the absolute frequency of twenty CO2 laser lines, with uncertainties between 100 Hz and 1 kHz mainly limited by the accuracy of the OsO4 grid. The set of measurements reveal some discrepancies with data based on measurements performed with the widely used saturated fluorescence technique; we attribute these to pressure shifts of several kilohertz under the conditions of this last method.

http://iopscience.iop.org/article/10.1088/0026-1394/34/4/4/pdf

CO2 laser stabilized on narrow saturated absorption resonances of CO2, improved absolute frequency measurements

The distribution and the comparison of an ultrastable reference frequency using optical fibres have been greatly improved in the last ten years. LNE-SYRTE and LPL (University Paris 13) have been pioneering the development of these new methods. In this paper we present a review of the methods and the results obtained. The frequency stability and accuracy of optical links surpass the well-established methods using GNSS and geostationary satellites. In this paper we show that it is possible to use public telecommunication network carrying Internet data to compare and distribute ultrastable metrological signals over long distances. In addition both frequency stability and accuracy are equivalent to those obtained with links developed with a dedicated fibre network. This novel technique paves the way to the deployment of a national and continental wide ultrastable metrological optical network.

/pdf/transfert-de-frequence-par-fibre-optique-en-metrologie-4xxdowgcm6.pdf

Ch. Daussy

Papers

Limit on the parity nonconserving energy difference between the enantiomers of a chiral molecule by laser spectroscopy

High resolution frequency standard dissemination via optical fiber metropolitan network

CO/sub 2/ laser stabilization to 0.1-Hz level using external electrooptic modulation

CO2 laser stabilized on narrow saturated absorption resonances of CO2, improved absolute frequency measurements

Transfert de fréquence par fibre optique en métrologie