225 research outputs found
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-precise measurement of optical frequency ratios
We developed a novel technique for frequency measurement and synthesis, based
on the operation of a femtosecond comb generator as transfer oscillator. The
technique can be used to measure frequency ratios of any optical signals
throughout the visible and near-infrared part of the spectrum. Relative
uncertainties of for averaging times of 100 s are possible. Using a
Nd:YAG laser in combination with a nonlinear crystal we measured the frequency
ratio of the second harmonic at 532 nm to the fundamental at
1064 nm, .Comment: 4 pages, 4 figure
Monitoring of the operating parameters of the KATRIN Windowless Gaseous Tritium Source
The Karlsruhe Tritium Neutrino (KATRIN) experiment will measure the absolute
mass scale of neutrinos with a sensitivity of \m_{\nu} = 200 meV/c by
high-precision spectroscopy close to the tritium beta-decay endpoint at 18.6
keV. Its Windowless Gaseous Tritium Source (WGTS) is a beta-decay source of
high intensity (/s) and stability, where high-purity molecular tritium
at 30 K is circulated in a closed loop with a yearly throughput of 10 kg. To
limit systematic effects the column density of the source has to be stabilised
at the 0.1% level. This requires extensive sensor instrumentation and dedicated
control and monitoring systems for parameters such as the beam tube
temperature, injection pressure, gas composition and others. Here we give an
overview of these systems including a dedicated Laser-Raman system as well as
several beta-decay activity monitors. We also report on results of the WGTS
demonstrator and other large-scale test experiments giving proof-of-principle
that all parameters relevant to the systematics can be controlled and monitored
on the 0.1% level or better. As a result of these works, the WGTS systematics
can be controlled within stringent margins, enabling the KATRIN experiment to
explore the neutrino mass scale with the design sensitivity.Comment: 32 pages, 13 figures. modification to title, typos correcte
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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