395 research outputs found

    Dynamical Spectroscopy of Transient He2 Molecules

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    The velocities of atoms can be manipulated by near-resonant laser light. After many absorption-spontaneous emission cycles momentum is transferred to the atoms in the direction of the laser beam. In this way atoms can be slowed down and cooled to milliKelvin temperatures and below. In three mutually orthogonal pairs of counter-propagating laser beams in combination with a magnetic field atoms can be cooled and trapped. In this so-called magneto-optical trap (MOT) two atoms can be excited to a molecular state by absorption of a photon. This technique is called photoassociation spectroscopy. In our case we study metastable helium atoms, which have a large internal energy. When two metastable helium atoms approach each other, one of the atoms ionizes and the ions are detected by a microchannelplates detector. When a probe laser beam is directed onto the MOT cloud and scanned in frequency, atom pairs can be excited to several ro-vibrational states. In the excited state the metastable helium atoms are accelerated towards each other and ionize at short internuclear distance. The ro-vibrational states appear as peaks in the ionization signal and from the position of these states information on the excited state interaction potential can be extracted

    Photo induced collisions with laser cooled He* atoms

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    This paper presents an experimental investigation of cold collisions between metastable Helium atoms in an optical trap at 1mK. Penning (PI) and associative (AI) ionization reactions are distinguished using a mass spectrometer and studied under influence of near resonant laser light. Sensitive behavior of the ion rate is observed when the laser is tuned close to resonance. Experimental ?ndings are well described, on an absolute scale, by a semi-classical model we have developed for optical collisions and by a modi?ed Julienne-ViguÂŽe model

    Foliebekisting maakt dubbelgekromde betonconstructies betaalbaar

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    Dubbel gekromde betonconstructies in civiele werken zien we steeds vaker in Nederland. Technisch zijn dergelijke constructies goed te maken, maar hoe houden we het betaalbaar? De bekisting en de stalen wapening zijn de duurste onderdelen van het productieproces. Om die kosten te drukken, doet constructie adviesbureau ABT onderzoek naar een nieuw type bekisting. Die bestaat uit folie

    Rotationally induced Penning ionization of ultracold photoassociated helium dimers

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    We have studied photoassociation of metastable \tripS helium atoms near the \tripS-\tripP asymptote by both ion detection in a magneto-optical trap and trap-loss measurements in a magnetic trap. A detailed comparison between the results of the two experiments gives insight into the mechanism of the Penning ionization process. We have identified four series of resonances corresponding to vibrational molecular levels belonging to different rotational states in two potentials. The corresponding spin states become quasi-purely quintet at small interatomic distance, and Penning ionization is inhibited by spin conservation rules. Only a weak rotational coupling is responsible for the contamination by singlet spin states leading to a detectable ion signal. However, for one of these series Bose statistics does not enable the rotational coupling and the series detected through trap-loss does not give rise to sufficient ionization for detection.Comment: 7 pages, 4 figures, submitted to EuroPhysics Letter

    On the Role of Penning Ionization in Photoassociation Spectroscopy

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    We study the role of Penning ionization on the photoassociation spectra of He(^3S)-He(^3S). The experimental setup is discussed and experimental results for different intensities of the probe laser are shown. For modelling the experimental results we consider coupled-channel calculations of the crossing of the ground state with the excited state at the Condon point. The coupled-channel calculations are first applied to model systems, where we consider two coupled channels without ionization, two coupled channels with ionization, and three coupled channels, for which only one of the excited states is ionizing. Finally, coupled-channel calculations are applied to photoassociation of He(^3S)-He(^3S) and good agreement is obtained between the model and the experimental results.Comment: 14 pages, 18 figures, submitted to the special issue on Cold Molecules of J. Phys.

    Frequency shifts of photoassociative spectra of ultracold metastable Helium atoms : a new measurement of the s-wave scattering length

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    We observe light-induced frequency shifts in one-color photoassociative spectra of magnetically trapped 4^4He∗^* atoms in the metastable 23S12^3S_1 state. A pair of ultracold spin-polarized 23S12^3S_1 helium atoms is excited into a molecular bound state in the purely long range 0u+0_u^+ potential connected to the 23S1−23P02^3S_1 - 2^3P_0 asymptote. The shift arises from the optical coupling of the molecular excited bound state with the scattering states and the bound states of two colliding 23S12^3S_1 atoms. We measure the frequency-shifts for several ro-vibrational levels in the 0u+0^+_u potential and find a linear dependence on the photoassociation laser intensity. Comparison with a theoretical analysis provides a good indication for the s-wave scattering length aa of the quintet (5ÎŁg+^5\Sigma_g^+) potential, a=7.2±0.6a=7.2\pm 0.6 nm, which is significantly lower than most previous results obtained by non-spectroscopic methods.Comment: 7 pages, 4 figure

    Development of novel low-mass module concepts based on MALTA monolithic pixel sensors

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    The MALTA CMOS monolithic silicon pixel sensors has been developed in the Tower 180 nm CMOS imaging process. It includes an asynchronous readout scheme and complies with the ATLAS inner tracker requirements for the HL-LHC. Several 4-chip MALTA modules have been built using Al wedge wire bonding to demonstrate the direct transfer of data from chip-to-chip and to read out the data of the entire module via one chip only. Novel technologies such as Anisotropic Conductive Films (ACF) and nanowires have been investigated to build a compact module. A lightweight flex with 17 {\mu}m trace spacing has been designed, allowing compact packaging with a direct attachment of the chip connection pads to the flex using these interconnection technologies. This contribution shows the current state of our work towards a flexible, low material, dense and reliable packaging and modularization of pixel detectors.Comment: 5 pages + 1 page references,8 figure

    MALTA monolithic pixel sensors in TowerJazz 180 nm technology

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    Depleted Monolithic Active Pixel Sensors are of highest interest at the HL-LHC and beyond for the replacement of the Pixel trackers in the outermost layers of experiments where the requirement on total area and cost effectiveness is much bigger. They aim to provide high granularity and low material budget over large surfaces with ease of integration. Our research focuses on MALTA, a radiation hard DMAPS with small collection electrode designed in TowerJazz 180 nm CMOS imaging technology and asynchronous read-out. Latest prototypes are radiation hard up to 2 × 1015 1 MeV neq/cm2 with a time resolution better than 2 ns

    Timing performance of radiation hard MALTA monolithic Pixel sensors

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    The MALTA family of Depleted Monolithic Active Pixel Sensor (DMAPS) produced in Tower 180 nm CMOS technology targets radiation hard applications for the HL-LHC and beyond. Several process modifications and front-end improvements have resulted in radiation hardness up to 2×1015 1 MeV neq/cm22 \times 10^{15}~1~\text{MeV}~\text{n}_{eq}/\text{cm}^2 and time resolution below 2 ns, with uniform charge collection efficiency across the Pixel of size 36.4×36.4 Όm236.4 \times 36.4~\mu\text{m}^2 with a 3 Όm23~\mu\text{m}^2 electrode size. The MALTA2 demonstrator produced in 2021 on high-resistivity epitaxial silicon and on Czochralski substrates implements a new cascoded front-end that reduces the RTS noise and has a higher gain. This contribution shows results from MALTA2 on timing resolution at the nanosecond level from the CERN SPS test-beam campaign of 2021.Comment: 8 pages, 8 figures. Submitted to Journal of Instrumentation (JINST). Proceedings of the 23rd International Workshop on Radiation Imaging Detectors IWORID 202

    Performance of the MALTA Telescope

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    MALTA is part of the Depleted Monolithic Active Pixel sensors designed in Tower 180nm CMOS imaging technology. A custom telescope with six MALTA planes has been developed for test beam campaigns at SPS, CERN, with the ability to host several devices under test. The telescope system has a dedicated custom readout, online monitoring integrated into DAQ with realtime hit map, time distribution and event hit multiplicity. It hosts a dedicated fully configurable trigger system enabling to trigger on coincidence between telescope planes and timing reference from a scintillator. The excellent time resolution performance allows for fast track reconstruction, due to the possibility to retain a low hit multiplicity per event which reduces the combinatorics. This paper reviews the architecture of the system and its performance during the 2021 and 2022 test beam campaign at the SPS North Area
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