Six European National Measurement Institutes (NMIs) have joined forces within the European Metrology Research Programme funded project NANOTRACE to develop the next generation of optical interferometers having a target uncertainty of 10 pm. These are needed for NMIs to provide improved traceable dimensional metrology that can be disseminated to the wider nanotechnology community, thereby supporting the growth in nanotechnology. Several approaches were followed in order to develop the interferometers. This paper briefly describes the different interferometers developed by the various partners and presents the results of a comparison of performance of the optical interferometers using an x-ray interferometer to generate traceable reference displacements.

Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc. ID XXXXX); published Month X, XXXXWe have detected and analyzed narrow, high contrast coherent population trapping resonances, which appear in transmission of the probe monochromatic light beam under action of the counterpropagating two-frequency laser radiation, on example of the nonclosed three level Λ-system formed by spectral components of the Doppler broadened D2 line of cesium atoms (in the cell with the rarefied Cs vapor). These nontrivial resonances are determined directly by the trapped atomic population on the definite lower level of the Λ-system and may be used in atomic frequency standards, sensitive magnetometers and in ultrahigh resolution laser spectroscopy of atoms and molecules.OCIS Codes: 030.1670, 120.4800, 140.3425, 300.6210, 300.6360 At the phenomenon of the coherent population trapping (CPT), a multilevel quantum system subject to decay processes is coherently driven into a superposition state immune from the further excitation, in which the system population is trapped. The CPT is the basis of a number of important applications: ultrahigh resolution spectroscopy, atomic clocks, magnetometry, optical switching, coherent cooling and trapping of atoms and also in some others described, for example in reviews [1][2][3]. In particular, narrow CPT resonances, detected in absorption of a twofrequency laser radiation (and also in the corresponding induced fluorescence spectrum of a gas medium) on three level atomic Λ-systems, are successfully applied in atomic frequency standards [4] and in high sensitive magnetometers [5]. For these applications, researchers use, mainly, vapors of alkali earth atoms (in particular Cs or Rb), whose ground quantum term consists of two sublevels of the hyperfine structure [6]. Resonance excitation of atoms on the Λ-system scheme is realized by means of the two-frequency radiation from given sublevels (Fig.1). Such Λ-systems are not closed because of presence of channels of the radiative decay of the excited state│3 > on some Zeeman sublevels of lower levels which don't interact with the two-frequency radiation [1][2][3]. Therefore highly narrow CPT resonances, recorded by known methods on the population of the upper level │3 > (Fig.1), have a comparatively small contrast on a more wide spectral background of absorption or fluorescence [4]. At the same time, more contrast CPT resonances may appear in dependences of populations of lower long-lived levels│1 > and │2 > of a nonclosed Λ-system (Fig.1) on the frequency difference (ω2 − ω1) of the bichromatic laser pumping. Indeed, let us consider interaction of such a system with 2 monochromatic laser fields. Frequencies ω1 and ω2 of given fields are close to centers Ω31 and Ω32 of electrodipole transitions │1 > − │3 > and │2 > − │3 > respectively (Fig.1). The population of this nonclosed Λ-system will be exhausted at intensification of the twofrequency laser pumping with the exception of a fraction of atoms, which may ...

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Lasers from nine national metrology institutes (NMIs) were compared as part of the CCL-K11 ongoing key comparison, initiated by the 13th meeting of the Comité Consultative des Longeurs (CCL) in 2007. The absolute frequency of the f component of the R(127) 11–5 transition of molecular iodine was measured for these lasers following the technical protocol for CCL-K11. The results of these measurements are compiled in the present report.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).