227 research outputs found
Accurate reference gas mixtures containing tritiated molecules: Their production and ramanâbased analysis
Highly accurate, quantitative analyses of mixtures of hydrogen isotopologuesâboth the stable species, H, D2, and HD, and the radioactive species, T, HT, and DTâare of great importance in fields as diverse as deuteriumâtritium fusion, neutrino mass measurements using tritium ÎČ-decay, or for photonuclear experiments in which hydrogenâdeuterium targets are used. In this publication we describe a production, handling, and analysis facility capable of fabricating well-defined gas samples, which may contain any of the stable and radioactive hydrogen isotopologues, with sub-percent accuracy for the relative species concentrations. The production is based on precise manometric gas mixing of H, D, and T. The heteronuclear isotopologues HD, HT, and DT are generated via controlled, in-line catalytic reaction or by ÎČ-induced self-equilibration, respectively. The analysis was carried out using an in-line intensity- and wavelength-calibrated Raman spectroscopy system. This allows for continuous monitoring of the composition of the circulating gas during the self-equilibration or catalytic evolution phases. During all procedures, effects, such as exchange reactions with wall materials, were considered with care. Together with measurement statistics, these and other systematic effects were included in the determination of composition uncertainties of the generated reference gas samples. Measurement and calibration accuracy at the level of 1% was achieved
Absolute fluorescence and absorption measurements over a dynamic range of 106 with cavity-enhanced laser-induced fluorescence
We present a novel spectroscopic technique that exhibits high sensitivity and a large dynamic range for the measurement of absolute absorption coefficients. We perform a simultaneous and correlated laser-induced fluorescence and cavity ring-down measurement of the same sample in a single pulsed laser beam. The combined measurement offers a large dynamic range and a lower limit of detection than either technique on its own. The methodology, dubbed cavity-enhanced laser-induced fluorescence, is developed and rigorously tested against the electronic spectroscopy of 1,4-bis(phenylethynyl)benzene in a molecular beam and density measurements in a cell. We outline how the method can be used to determine absolute quantities, such as sample densities, absorption cross sections, and fluorescence quantum yields, particularly in spatially confined samples
Ultra-cold atoms in an optical cavity: two-mode laser locking to the cavity avoiding radiation pressure
The combination of ultra-cold atomic clouds with the light fields of optical
cavities provides a powerful model system for the development of new types of
laser cooling and for studying cooperative phenomena. These experiments
critically depend on the precise tuning of an incident pump laser with respect
to a cavity resonance. Here, we present a simple and reliable experimental
tuning scheme based on a two-mode laser spectrometer. The scheme uses a first
laser for probing higher-order transversal modes of the cavity having an
intensity minimum near the cavity's optical axis, where the atoms are confined
by a magnetic trap. In this way the cavity resonance is observed without
exposing the atoms to unwanted radiation pressure. A second laser, which is
phase-locked to the first one and tuned close to a fundamental cavity mode
drives the coherent atom-field dynamics.Comment: 7 pages, 7 figure
Commissioning of the vacuum system of the KATRIN Main Spectrometer
The KATRIN experiment will probe the neutrino mass by measuring the
beta-electron energy spectrum near the endpoint of tritium beta-decay. An
integral energy analysis will be performed by an electro-static spectrometer
(Main Spectrometer), an ultra-high vacuum vessel with a length of 23.2 m, a
volume of 1240 m^3, and a complex inner electrode system with about 120000
individual parts. The strong magnetic field that guides the beta-electrons is
provided by super-conducting solenoids at both ends of the spectrometer. Its
influence on turbo-molecular pumps and vacuum gauges had to be considered. A
system consisting of 6 turbo-molecular pumps and 3 km of non-evaporable getter
strips has been deployed and was tested during the commissioning of the
spectrometer. In this paper the configuration, the commissioning with bake-out
at 300{\deg}C, and the performance of this system are presented in detail. The
vacuum system has to maintain a pressure in the 10^{-11} mbar range. It is
demonstrated that the performance of the system is already close to these
stringent functional requirements for the KATRIN experiment, which will start
at the end of 2016.Comment: submitted for publication in JINST, 39 pages, 15 figure
Phase- coherent comparison of two optical frequency standards over 146 km using a telecommunication fiber link
We have explored the performance of two "dark fibers" of a commercial
telecommunication fiber link for a remote comparison of optical clocks. The two
fibers, linking the Leibniz University of Hanover (LUH) with the
Physi-kalisch-Technische Bundesanstalt (PTB) in Braunschweig, are connected in
Hanover to form a total fiber length of 146 km. At PTB the performance of an
optical frequency standard operating at 456 THz was imprinted to a cw trans-fer
laser at 194 THz, and its frequency was transmitted over the fiber. In order to
detect and compensate phase noise related to the optical fiber link we have
built a low-noise optical fiber interferometer and investigated noise sources
that affect the overall performance of the optical link. The frequency
stability at the remote end has been measured using the clock laser of PTB's
Yb+ frequency standard operating at 344 THz. We show that the frequency of a
frequency-stabilized fiber laser can be transmitted over a total fiber length
of 146 km with a relative frequency uncertainty below 1E-19, and short term
frequency instability given by the fractional Allan deviation of
sy(t)=3.3E-15/(t/s)
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