Complete characterization of weak, ultrashort near-UV pulses by spectral interferometry

We present a method for a complete characterization of a femtosecond ultraviolet pulse when a fundamental near-infrared beam is also available. Our approach relies on generation of second harmonic from the pre-characterized fundamental, which serves as a reference against which an unknown pulse is measured using spectral interference (SI). The characterization apparatus is a modified second harmonic frequency resolved optical gating setup which additionally allows for taking SI spectrum. The presented method is linear in the unknown field, simple and sensitive. We checked its accuracy using test pulses generated in a thick nonlinear crystal, demonstrating the ability to measure the phase in a broad spectral range, down to 0.1% peak spectral intensity as well as retrieving pi leaps in the spectral phase

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$^2$ 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 ($10^{11}$/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

Gamma-induced background in the KATRIN main spectrometer

International audienceThe KArlsruhe TRItium Neutrino (KATRIN) experiment aims to make a model-independent determination of the effective electron antineutrino mass with a sensitivity of 0.2 eV/c 2 . It investigates the kinematics of β -particles from tritium β -decay close to the endpoint of the energy spectrum. Because the KATRIN main spectrometer (MS) is located above ground, muon-induced backgrounds are of particular concern. Coincidence measurements with the MS and a scintillator-based muon detector system confirmed the model of secondary electron production by cosmic-ray muons inside the MS. Correlation measurements with the same setup showed that about 12% of secondary electrons emitted from the inner surface are induced by cosmic-ray muons, with approximately one secondary electron produced for every 17 muon crossings. However, the magnetic and electrostatic shielding of the MS is able to efficiently suppress these electrons, and we find that muons are responsible for less than 17% (90% confidence level) of the overall MS background

The design, construction, and commissioning of the KATRIN experiment

The KArlsruhe TRItium Neutrino (KATRIN) experiment, which aims to make a direct and model-independent determination of the absolute neutrino mass scale, is a complex experiment with many components. More than 15 years ago, we published a technical design report (TDR) [1] to describe the hardware design and requirements to achieve our sensitivity goal of 0.2 eV at 90% C.L. on the neutrino mass. Since then there has been considerable progress, culminating in the publication of first neutrino mass results with the entire beamline operating [2]. In this paper, we document the current state of all completed beamline components (as of the first neutrino mass measurement campaign), demonstrate our ability to reliably and stably control them over long times, and present details on their respective commissioning campaigns

SPECTROSCOPIC PROBING OF POTENTIAL SURFACES IN REACTIVE COLLISIONS

Depuis quelque temps les méthodes spectroscopiques apportent des résultats remarquables concernant les états intermédiaires instables, ABC*, qui forment les "états de transition" dans des collisions réactives simples. Dans un traitement (relativement) simple l'"état de transition" résulte de la photodissociation de la molécule et on construit les potentiels d'interaction durant le processus de séparation des fragments (demi-collision) avec émission ou absorption de photons. La méthode est illustrée par l'exemple de la photolyse NaI, donnant lieu à une photoémission du composé intermédiaire NaI≠*. Pour les collisions réactives, où l'on peut rencontrer de nombreuses surfaces de potentiel, on a réalisé récemment des progrès prometteurs. L'état actuel des efforts de recherche théorique et expérimental sera discuté dans le cadre de quelques réactions d'échange telles que H+H2, Mg+H2, Hg+Cl2 et K+NaCl.For the investigation of unstable intermediates, ABC*, which constitute the "transition states" in some simple reactive collisions, spectroscopic methods are beginning to provide valuable results. In a (relatively) simple approach molecules are photodissociated, and the interaction potentials during the process of separation (half-collision) are mapped in either absorption or emission ; the method will be described exemplary for the photolysis of NaI, giving rise to emission from NaI≠*. For reactive collisions, where a manyfold of potentials may be encountered, some promising progres shas been achieved recently. The current status of some theoretical and experimental efforts will be discussed for a number of exchange reactions, e.g., H+H2, Mg+HS2, Hg+Cl2, K+NaCl

Vibrational excitation of adsorbed molecules by photoelectrons of very low energy: Acrylonitrile on Cu (100)

In this study, we report on a powerful method of primary photoelectron scattering by adsorbed species. Specifically, threshold-energy (E kin,max < 0.5 eV) two-photon photoelectrons (2PPE) are used to probe acrylonitrile (ACN) molecules chemisorbed onto a Cu(100) substrate, held at room temperature. This has proven to constitute a perfect tool to reveal the ACN vibrational modes in the chemisorbed state. From the dynamics of the directional (perpendicular to the copper surface) electron energy loss we conclude that only a few fundamental vibrational motions of adsorbed ACN are excited, namely the CC, CN and C-H stretch modes. From the excitation probability spectra threshold energies, Eth, of these modes was extracted: Eth(CC) = 182(15) meV, Eth(CN) = 248(16) meV - which are shifted noticeably from the equivalent gas phase values; and E th(C-H) ∼360-380 meV - which varies only marginally from the gas phase value. The interpretation of the excitation spectra suggests that the di-σ adsorption configuration of the terminal C- and N-atoms dominates, which agrees well with the orientation and bindings predicted in Density Functional Theory (DFT) calculations. Consistent with this is the observation that the contribution to the 2PPE excitation spectra from the C-H stretch motion is by far the largest, which are not directly affected by chemisorption bonding. © 2011 the Owner Societies.This research received financial support from the Ministerio de Ciencia y Tecnología of Spain (grants CSD2009-00038 and CTQ2007-61749) and from the Santander-Complutense University research grant programme. J. T. acknowledges a PhD fellowship from the Ministerio de Educación y Ciencia of Spain.Peer Reviewe

High-resolution spectroscopy of gaseous 83m^\mathrm{83m}Kr conversion electrons with the KATRIN experiment

International audienceIn this work, we present the first spectroscopic measurements of conversion electrons originating from the decay of metastable gaseous 83mKr with the Karlsruhe Tritium Neutrino (KATRIN) experiment. The obtained results represent one of the major commissioning milestones for the subsequent direct neutrino mass measurement with KATRIN. The successful campaign demonstrates the functionalities of the KATRIN beamline. Precise measurement of the narrow K-32, L3-32, and N2,3-32 conversion electron lines allowed to verify the eV-scale energy resolution of the KATRIN main spectrometer necessary for competitive measurement of the absolute neutrino mass scale