53 research outputs found
Evidence for speed-dependent effects in NH3 self-broadened spectra: towards a new determination of the Boltzmann constant
In this paper we present an accurate analysis of the shape of an isolated
rovibrational ammonia line from the strong nu2 band around 10 m, 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 NH3. Accurate lineshape parameters of the nu2 saQ(6,3)
line are obtained. Our current project aiming at measuring the Boltzmann
constant, kB, by laser spectroscopy will straight away benefit from such
knowledge. We anticipate that a first optical determination of kB with a
competitive uncertainty of a few ppm is now reachable.Comment: 13 pages, 5 figures, 1 tabl
Probing weak force induced parity violation by high resolution mid-infrared molecular spectroscopy
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
Determination of the Boltzmann constant by laser spectroscopy as a basis for future measurements of the thermodynamic temperature
In this paper, we present the latest results on the measurement of the
Boltzmann constant kB, by laser spectroscopy of ammonia at 10 ?m. The Doppler
absorption profile of a ro-vibrational line of an NH3 gas sample at thermal and
pressure equilibrium is measured as accurately as possible. The absorption cell
is placed inside a large 1m3 thermostat filled with an ice-water mixture, which
sets the temperature very close to 273.15 K. Analysing this profile, which is
related to the Maxwell-Boltzmann molecular speed distribution, leads to a
determination of the Boltzmann constant via a measurement of the Doppler width
(proportional tosqrt(kBT)). A spectroscopic determination of the Boltzmann
constant with an uncertainty as low as 37 ppm is obtained. Recent improvements
with a new passive thermostat lead to a temperature accuracy, stability and
homogeneity of the absorption cell better than 1 ppm over a day
Mid-IR frequency measurement using an optical frequency comb and a long-distance remote frequency reference
We have built a frequency chain which enables to measure the absolute
frequency of a laser emitting in the 28-31 THz frequency range and stabilized
onto a molecular absorption line. The set-up uses an optical frequency comb and
an ultrastable 1.55 m frequency reference signal, transferred from
LNE-SYRTE to LPL through an optical link. We are now progressing towards the
stabilization of the mid-IR laser via the frequency comb and the extension of
this technique to quantum cascade lasers. Such a development is very
challenging for ultrahigh resolution molecular spectroscopy and fundamental
tests of physics with molecules
A revised uncertainty budget for measuring the Boltzmann constant using the Doppler Broadening Technique on ammonia
We report on our on-going effort to measure the Boltzmann constant, kB, 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 kB
at the part per million accuracy level are outlined
Measurement of the Boltzmann constant by the Doppler broadening technique at a 3,8x10-5 accuracy level
In this paper, we describe an experiment performed at the Laboratoire de
Physique des Lasers and dedicated to an optical measurement of the Boltzmann
constant. With the proposed innovative technique, determining comes down to an
ordinary frequency measurement. The method consists in measuring as accurately
as possible the Doppler absorption profile of a rovibrational line of ammonia
in thermal equilibrium. This profile is related to the Maxwell-Boltzmann
molecular velocity distribution along the laser beam. A fit of the absorption
line shape leads to a determination of the Doppler width proportional to
sqrt(kT) and thus to a determination of the Boltzmann constant. The laser
source is an ultra-stable CO2 laser with a wavelength . The absorption cell is
placed in a thermostat keeping the temperature at 273.15 K within 1.4 mK. We
were able to measure with a relative uncertainty as small as 3.8x10-5, which
represents an improvement of an order of magnitude for an integration time
comparable to our previous measurement published in 2007 [1
A widely tunable 10-m quantum cascade laser phase-locked to a state-of-the-art mid-infrared reference for precision molecular spectroscopy
We report the coherent phase-locking of a quantum cascade laser (QCL) at
10-m to the secondary frequency standard of this spectral region, a CO2
laser stabilized on a saturated absorption line of OsO4. 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 NH3 and methyltrioxorhenium, two species of interest for applications in
precision measurements.Comment: 5 pages, 4 figure
Accurate determination of the Boltzmann constant by Doppler spectroscopy: Towards a new definition of the kelvin
proceedings of the ICAP 2012 conference (23rd International Conference on Atomic Physics)International audienceAccurate molecular spectroscopy in the mid-infrared region allows precision measurements of fundamental constants. For instance, measuring the linewidth of an isolated Doppler-broadened absorption line of ammonia around 10 µm enables a determination of the Boltzmann constant k B. We report on our latest measurements. By fitting this lineshape to several models which include Dicke narrowing or speed-dependent collisional effects, we find that a determination of k B with an uncertainty of a few ppm is reachable. This is comparable to the best current uncertainty obtained using acoustic methods and would make a significant contribution to any new value of k B determined by the CODATA. Furthermore, having multiple independent measurements at these accuracies opens the possibility of defining the kelvin by fixing k B , an exciting prospect considering the upcoming redefinition of the International System of Units
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