Long-distance frequency transfer over an urban fiber link using optical phase stabilization

We transferred the frequency of an ultra-stable laser over 86 km of urban fiber. The link is composed of two cascaded 43-km fibers connecting two laboratories, LNE-SYRTE and LPL in Paris area. In an effort to realistically demonstrate a link of 172 km without using spooled fiber extensions, we implemented a recirculation loop to double the length of the urban fiber link. The link is fed with a 1542-nm cavity stabilized fiber laser having a sub-Hz linewidth. The fiber-induced phase noise is measured and cancelled with an all fiber-based interferometer using commercial off the shelf pigtailed telecommunication components. The compensated link shows an Allan deviation of a few 10-16 at one second and a few 10-19 at 10,000 seconds

Progress towards an accurate determination of the Boltzmann constant by Doppler spectroscopy

In this paper, we present significant progress performed on an experiment dedicated to the determination of the Boltzmann constant, k, by accurately measuring the Doppler absorption profile of a line in a gas of ammonia at thermal equilibrium. This optical method based on the first principles of statistical mechanics is an alternative to the acoustical method which has led to the unique determination of k published by the CODATA with a relative accuracy of 1.7 ppm. We report on the first measurement of the Boltzmann constant by laser spectroscopy with a statistical uncertainty below 10 ppm, more specifically 6.4 ppm. This progress results from improvements in the detection method and in the statistical treatment of the data. In addition, we have recorded the hyperfine structure of the probed saQ(6,3) rovibrational line of ammonia by saturation spectroscopy and thus determine very precisely the induced 4.36 (2) ppm broadening of the absorption linewidth. We also show that, in our well chosen experimental conditions, saturation effects have a negligible impact on the linewidth. Finally, we draw the route to future developments for an absolute determination of with an accuracy of a few ppm.Comment: 22 pages, 11 figure

Education can improve the negative perception of a threatened long-lived scavenging bird, the Andean condor

Human-wildlife conflicts currently represent one of the main conservation problems for wildlife species around the world. Vultures have serious conservation concerns, many of which are related to people's adverse perception about them due to the belief that they prey on livestock. Our aim was to assess local perception and the factors influencing people's perception of the largest scavenging bird in South America, the Andean condor. For this, we interviewed 112 people from Valle Fértil, San Juan province, a rural area of central west Argentina. Overall, people in the area mostly have an elementary education, and their most important activity is livestock rearing. The results showed that, in general, most people perceive the Andean condor as an injurious species and, in fact, some people recognize that they still kill condors. We identified two major factors that affect this perception, the education level of villagers and their relationship with livestock ranching. Our study suggests that conservation of condors and other similar scavengers depends on education programs designed to change the negative perception people have about them. Such programs should be particularly focused on ranchers since they are the ones who have the worst perception of these scavengers. We suggest that highlighting the central ecological role of scavengers and recovering their cultural value would be fundamental to reverse their persecution and their negative perception by people.Fil: Cailly Arnulphi, Verónica Beatríz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; ArgentinaFil: Lambertucci, Sergio Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Borghi, Carlos Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentin

Première observation de la structure hyperfine magnétique dans le spectre infrarouge de l'ammoniac

We give the first experimental observation of a magnetic hyperfine structure in the infrared spectrum of ammonia through saturation spectroscopy. The ν 2 as R(2,0) transition of 15NH3 in close coincidence with the 10R(42) CO2 laser line has been recorded with a 2 kHz halfwidth, which was limited by the molecular transit time across the laser beam. The observed spectrum appeared to be very sensitive to an external magnetic field so that the earth field has to be compensated.Nous présentons la première observation expérimentale, par spectroscopie de saturation, de la structure hyperfine magnétique dans le spectre infrarouge de l'ammoniac. Le spectre de la transition as R(2,0) de la bande ν 2 de 15NH3, en quasi-coïncidence avec la raie 10R(42) du laser à CO2, a été enregistré avec une demi-largeur de raie de 2 kHz, limitée par le temps de vol des molécules à travers le faisceau laser. Ce spectre s'est avéré très sensible à un champ magnétique extérieur de sorte que le champ terrestre a dû être compensé

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

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

Limit on the Parity Nonconserving Energy Difference between the Enantiomers of a Chiral Molecule by Laser Spectroscopy

International audienceWe 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 μm spectral range. The frequencies of saturation resonances of separated enantiomers have been compared and found to be identical within 13 Hz (Δν/ν<4.10−13)

Improved sensitivity in the search for a parity-violating energy difference in the vibrational spectrum of the enantiomers of CHFClBr

The theoretical prediction that enantiomers of chiral molecules have different spectra because of parity violation associated with neutral currents in the weak interaction has been experimentally looked for. Last searches of a frequency difference in the vibrational spectrum of the enantiomers of CHFClBr obtained with our infrared saturation spectrometer is presented. The frequencies of a saturation resonance of separated enantiomers of CHFClBr have been compared at a $5\times10^{-14}$ level. A residual pressure shift probably induced by uncontrolled impurities of the samples has been observed and found to limit our experimental sensitivity. Finally no parity violating frequency difference is observed within the present sensitivity of $2.5\times10^{-13}$. A new experimental scheme is proposed which should let the parity violation effect observable