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In this paper we present an accurate analysis of the shape of an isolated rovibrational ammonia line from the strong 2 band around 10 µm, recorded by laser absorption spectroscopy. Experimental spectra obtained under controlled temperature and pressure, are confronted to various models that take into account Dicke narrowing or speed-dependent effects. Our results show clear evidence for speed-dependent broadening and shifting, which had never been demonstrated so far in NH 3 . Accurate lineshape parameters of the ν 2 saQ(6,3) line are obtained. Our current project aiming at measuring the Boltzmann constant, k B , by laser spectroscopy will straight away benefit from such knowledge. We anticipate that a first optical determination of k B with a competitive uncertainty of a few ppm is now reachable.

We report the coherent phase-locking of a quantum cascade laser (QCL) at 10-µm to the secondary frequency standard of this spectral region, a CO 2 laser stabilized on a saturated absorption line of OsO 4 . The stability and accuracy of the standard are transferred to the QCL resulting in a line width of the order of 10 Hz, and leading to our knowledge to the narrowest QCL to date. The locked QCL is then used to perform absorption spectroscopy spanning 6 GHz of NH 3 and methyltrioxorhenium, two species of interest for applications in precision measurements.With their rich internal structure, molecules can play a decisive role in precision tests of fundamental physics. They are being used to test fundamental symmetries such as parity 1-3 or parity and time reversal 4 , to measure absolute values of fundamental constants 5-7 and their possible temporal variation [8][9][10] . Many of these experiments can be cast as measurements of resonance frequencies of molecular transitions, for which ultra-stable and accurate sources in the mid-infrared (mid-IR) are highly desirable, since most rovibrational transitions are to be found in that region.Our group has a long-standing interest in performing spectroscopic precision measurements on molecules at extreme resolutions around 10 µm 1,9,11 . We are currently working on two such measurements: the determination of the Boltzmann constant, k B , by Doppler spectroscopy of ammonia 6,12 and the first observation of parity violation by Ramsey interferometry of a beam of chiral molecules 3,13 . For these experiments, we currently use spectrometers based on custom built ultra-stable CO 2 lasers. We obtain the required metrological frequency stability and accuracy -10 Hz line width, 1 Hz stability at 1 s, accuracy of a few tens of hertz 14,15 -by stabilizing these lasers to saturated absorption lines of molecules such as OsO 4 . CO 2 lasers have a major shortcoming: a lack of tunability. They emit at CO 2 molecular resonances. An emission line is found every 30 to 50 GHz in the 9-11 µm wavelength range, and each line is tunable over about 100 MHz. Although, as in our spectrometers, this range can be extended a few gigahertz using electrooptical modulators (EOMs), this is done at the expense of power (EOMs at these wavelengths have an efficiency of 10 −4 ) and necessitates subsequent spectral filtering. Overcoming these difficulties without the loss of stability is key to enabling precision measurements in the mid-IR.One solution would be to use frequency combreferenced continuous-wave (cw) [16][17][18] or femtosecond mid-IR sources. These are based on frequency mixing in nonlinear crystals and provide absolute-frequency referencing, reasonable line widths and tunability, but are very complex and often exhibit limited power. By comparison, cw quantum cascade lasers (QCLs) are a new mature and robust technology that offer broad and continuous tuning over several hundred gigahertz at 100 mW-level powers. Several can be combined giving access to the whole mid-IR region. Recent studies of...

A theoretical model of the influence of detection bandwidth properties on observed line shapes in laser absorption spectroscopy is described. The model predicts artificial frequency shifts, extra broadenings and line asymmetries which must be taken into account in order to obtain accurate central frequencies and other spectroscopic parameters. This reveals sources of systematic effects most probably underestimated so far potentially affecting spectroscopic measurements. This may impact many fields of research, from atmospheric and interstellar physics to precision spectroscopic measurements devoted to metrological applications, tests of quantum electrodynamics or other fundamental laws of nature. Our theoretical model is validated by linear absorption experiments performed on H 2 O and NH 3 molecular lines recorded by precision laser spectroscopy in two distinct spectral regions, nearand mid-infrared. Possible means of recovering original line shape parameters or experimental conditions under which the detection bandwidth has a negligible impact, given a targeted accuracy, are proposed. Particular emphasis is put on the detection bandwidth adjustments required to use such high-quality molecular spectra for a spectroscopic determination of the Boltzmann constant at the 1 ppm level of accuracy.

Abstract:Despite periodic violent conflict between farmers and Fulani herders in many parts of Ghana, cooperative relations between them remain strong. They are “cultural neighbors” who cooperate both in times of violent conflict and during periods of no conflict. Cooperation between them is expressed through everyday interactions, cattle entrustment, resource sharing, trade, friendship, intermarriages, visitations, exchanges, communal labor, and social solidarity. Borrowing from theorizations of cultural neighborhood and everyday peace, this paper uses specific case studies from Northern and Southern Ghana to illustrate the enactment of cooperation between herders and farmers in areas of violent farmer-herder conflict.

Abstract:The impacts of environmental change and degradation on human populations, including the possibility of sharp increases in the number of people considered "environmental migrants" have gained considerable attention. Migrating communities may try to distribute their members along particular lines of kinship, gender, marriage and/or services linked to land exploitation and agriculture. This paper explores archives and narratives of African migrants in northwestern Benin and northeastern Ghana. These regions have been marked by severe ecological change and resource deterioration over the years, as well as changes in marital patterns, family relations and customary practices. In the case of Benin, the paper looks at different ethnic groups that migrated from neighboring countries to the study region. It then focuses on the Biali, who undertake marriage journeys after practicing rituals, which are often related to agricultural activities. The Frafra (Ghana), who, in their bid to out-migrate as a livelihood/coping strategy in the advent of environmental deterioration and rainfall variability, are confronted with high bride prices, changing family relations and customary practices. The paper concludes by highlighting socio-cultural changes that ensue in the face of outmigration among different ethnic groups, especially the Biali and Frafra, and the relationship between non-environmental and environmental factors, and mobility strategies. OPEN ACCESSSustainability 2014, 6 376

We report on our on-going effort to measure the Boltzmann constant, k B , using the Doppler Broadening Technique. The main systematic effects affecting the measurement are discussed. A revised error budget is presented in which the global uncertainty on systematic effects is reduced to 2.3 ppm. This corresponds to a reduction of more than one order of magnitude compared to our previous Boltzmann constant measurement. Means to reach a determination of k B at the part per million accuracy level are outlined.

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