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Wolff W, Dogan M, Luna H, Coutinho LH, Mootheril D, Baek W, Pfeifer T, Dorn A. Absolute electron impact ionization cross-sections for CF4: Three dimensional recoil-ion imaging combined with the relative flow technique. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2024; 95:095103. [PMID: 39230363 DOI: 10.1063/5.0219527] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2024] [Accepted: 08/05/2024] [Indexed: 09/05/2024]
Abstract
Here we present measurements of dissociative and non-dissociative cross-sections for the electron impact of the CF4 molecule. The present experiments are based on a Recoil Ion Momentum Spectrometer (RIMS), a standard gas mixing setup for CF4, and a reference gas. The measurements were carried out at several electron energies up to 1 keV, covering the energy range of previous experiments. We apply the relative flow technique (RFT) to convert the relative cross-sections measured by the RIMS into absolute values. Using the combination of RIMS and RFT, ion collection and calibration errors were minimized. The results were compared with theoretical and experimental studies available in the literature. Previous electron impact experiments present relative cross-sections or use correction terms for the absolute cross-sections due to losses of energetic ions. We elucidate the differences between the new measurement method and the existing ones in the literature and explain why the present method can be considered reliable. Furthermore, we show how reducing correction terms affects the results.
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Oelmann JH, Guth L, Heldt T, Griesbach N, Hector R, Lackmann N, Nauta J, Pfeifer T, Crespo López-Urrutia JR. Closed-cycle noble gas recycling system for high-repetition rate high-harmonic generation. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2024; 95:035115. [PMID: 38477653 DOI: 10.1063/5.0176563] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Accepted: 02/20/2024] [Indexed: 03/14/2024]
Abstract
We present a compact closed-loop recycling system for noble and inert gases. It has been developed for an extreme-ultraviolet (XUV) frequency comb based on high-harmonic generation at 100 MHz repetition rate. The system collects gas injected at several bars of backing pressure through a micrometer-sized nozzle into the laser-interaction region with a differential pumping system comprising turbomolecular pumps, and subsequently compresses the gas to a pressure of up to 200 bar. By drastically reducing the waste of expensive gases such as xenon and krypton, it enables the long operation times needed for spectroscopic measurements, as well as for continuous operation of the XUV frequency comb.
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Guillemin R, Inhester L, Ilchen M, Mazza T, Boll R, Weber T, Eckart S, Grychtol P, Rennhack N, Marchenko T, Velasquez N, Travnikova O, Ismail I, Niskanen J, Kukk E, Trinter F, Gisselbrecht M, Feifel R, Sansone G, Rolles D, Martins M, Meyer M, Simon M, Santra R, Pfeifer T, Jahnke T, Piancastelli MN. Isotope effects in dynamics of water isotopologues induced by core ionization at an x-ray free-electron laser. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2023; 10:054302. [PMID: 37799711 PMCID: PMC10550338 DOI: 10.1063/4.0000197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Accepted: 09/05/2023] [Indexed: 10/07/2023]
Abstract
Dynamical response of water exposed to x-rays is of utmost importance in a wealth of science areas. We exposed isolated water isotopologues to short x-ray pulses from a free-electron laser and detected momenta of all produced ions in coincidence. By combining experimental results and theoretical modeling, we identify significant structural dynamics with characteristic isotope effects in H2O2+, D2O2+, and HDO2+, such as asymmetric bond elongation and bond-angle opening, leading to two-body or three-body fragmentation on a timescale of a few femtoseconds. A method to disentangle the sequences of events taking place upon the consecutive absorption of two x-ray photons is described. The obtained deep look into structural properties and dynamics of dissociating water isotopologues provides essential insights into the underlying mechanisms.
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Ertel D, Schmoll M, Kellerer S, Jäger A, Weissenbilder R, Moioli M, Ahmadi H, Busto D, Makos I, Frassetto F, Poletto L, Schröter CD, Pfeifer T, Moshammer R, Sansone G. Ultrastable, high-repetition-rate attosecond beamline for time-resolved XUV-IR coincidence spectroscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2023; 94:073001. [PMID: 37404094 DOI: 10.1063/5.0139496] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Accepted: 05/30/2023] [Indexed: 07/06/2023]
Abstract
The implementation of attosecond photoelectron-photoion coincidence spectroscopy for the investigation of atomic and molecular dynamics calls for a high-repetition-rate driving source combined with experimental setups characterized by excellent stability for data acquisition over time intervals ranging from a few hours up to a few days. This requirement is crucial for the investigation of processes characterized by low cross sections and for the characterization of fully differential photoelectron(s) and photoion(s) angular and energy distributions. We demonstrate that the implementation of industrial-grade lasers, combined with a careful design of the delay line implemented in the pump-probe setup, allows one to reach ultrastable experimental conditions leading to an error in the estimation of the time delays of only 12 as over an acquisition time of 6.5 h. This result opens up new possibilities for the investigation of attosecond dynamics in simple quantum systems.
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Oelmann JH, Heldt T, Guth L, Nauta J, Lackmann N, Wössner V, Kokh S, Pfeifer T, López-Urrutia JRC. Photoelectron tomography with an intra-cavity velocity-map imaging spectrometer at 100 MHz repetition rate. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2022; 93:123303. [PMID: 36586896 DOI: 10.1063/5.0104679] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Accepted: 11/16/2022] [Indexed: 06/17/2023]
Abstract
We present a compact velocity-map imaging (VMI) spectrometer for photoelectron imaging at 100 MHz repetition rate. Ultrashort pulses from a near-infrared frequency comb laser are amplified in a polarization-insensitive passive femtosecond enhancement cavity. In the focus, multi-photon ionization (MPI) of gas-phase atoms is studied tomographically by rotating the laser polarization. We demonstrate the functioning of the VMI spectrometer by reconstructing photoelectron angular momentum distributions from xenon MPI. Our intra-cavity VMI setup collects electron energy spectra at high rates, with the advantage of transferring the coherence of the cavity-stabilized femtosecond pulses to the electrons. In addition, the setup will allow studies of strong-field effects in nanometric tips.
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Stierhof J, Kühn S, Winter M, Micke P, Steinbrügge R, Shah C, Hell N, Bissinger M, Hirsch M, Ballhausen R, Lang M, Gräfe C, Wipf S, Cumbee R, Betancourt-Martinez GL, Park S, Niskanen J, Chung M, Porter FS, Stöhlker T, Pfeifer T, Brown GV, Bernitt S, Hansmann P, Wilms J, Crespo López-Urrutia JR, Leutenegger MA. A new benchmark of soft X-ray transition energies of Ne , CO 2 , and SF 6 : paving a pathway towards ppm accuracy. THE EUROPEAN PHYSICAL JOURNAL. D, ATOMIC, MOLECULAR, AND OPTICAL PHYSICS 2022; 76:38. [PMID: 35273463 PMCID: PMC8888507 DOI: 10.1140/epjd/s10053-022-00355-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Accepted: 01/23/2022] [Indexed: 06/14/2023]
Abstract
ABSTRACT A key requirement for the correct interpretation of high-resolution X-ray spectra is that transition energies are known with high accuracy and precision. We investigate the K-shell features of Ne , CO 2 , and SF 6 gases, by measuring their photo ion-yield spectra at the BESSY II synchrotron facility simultaneously with the 1s-np fluorescence emission of He-like ions produced in the Polar-X EBIT. Accurate ab initio calculations of transitions in these ions provide the basis of the calibration. While the CO 2 result agrees well with previous measurements, the SF 6 spectrum appears shifted by ∼ 0.5 eV, about twice the uncertainty of the earlier results. Our result for Ne shows a large departure from earlier results, but may suffer from larger systematic effects than our other measurements. The molecular spectra agree well with our results of time-dependent density functional theory. We find that the statistical uncertainty allows calibrations in the desired range of 1-10 meV, however, systematic contributions still limit the uncertainty to ∼ 40-100 meV, mainly due to the temporal stability of the monochromator energy scale. Combining our absolute calibration technique with a relative energy calibration technique such as photoelectron energy spectroscopy will be necessary to realize its full potential of achieving uncertainties as low as 1-10 meV.
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Schotsch F, Zebergs I, Augustin S, Lindenblatt H, Hoibl L, Djendjur D, Schroeter CD, Pfeifer T, Moshammer R. TrapREMI: A reaction microscope inside an electrostatic ion beam trap. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:123201. [PMID: 34972421 DOI: 10.1063/5.0065454] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Accepted: 11/04/2021] [Indexed: 06/14/2023]
Abstract
A new experimental setup has been developed to investigate the reactions of molecular ions and charged clusters with a variety of projectile beams. An Electrostatic Ion Beam Trap (EIBT) stores fast ions at keV energies in an oscillatory motion. By crossing it with a projectile beam, e.g., an IR laser, molecular reactions can be induced. We implemented a Reaction Microscope (REMI) in the field-free region of the EIBT to perform coincidence spectroscopy on the resulting reaction products. In contrast to prior experiments, this unique combination of techniques allows us to measure the 3D momentum-vectors of ions, electrons, and neutrals as reaction products in coincidence. At the same time, the EIBT allows for advanced target preparation techniques, e.g., relaxation of hot molecules during storage times of up to seconds, autoresonance cooling, and recycling of target species, which are difficult to prepare. Otherwise, the TrapREMI setup can be connected to a variety of projectile sources, e.g., atomic gas jets, large-scale radiation facilities, and ultrashort laser pulses, which enable even time-resolved studies. Here, we describe the setup and a first photodissociation experiment on H2 +, which demonstrates the ion-neutral coincidence detection in the TrapREMI.
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Kurz N, Fischer D, Pfeifer T, Dorn A. Reaction microscope for investigating ionization dynamics of weakly bound alkali dimers. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:123202. [PMID: 34972432 DOI: 10.1063/5.0069506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Accepted: 11/12/2021] [Indexed: 06/14/2023]
Abstract
We report on the implementation of a far-off-resonant, optical dipole force trap in a reaction microscope combined with a magneto-optical trap. Kinematically complete multi-photon ionization experiments were performed on optically trapped 6Li atoms and photo-associated 6Li2 molecules in their highest vibrational state. The apparatus allows us to distinguish different ionization mechanisms related to the presence of the IR field of the optical dipole trap that can occur during ionization of 6Li and 6Li2 in strong fields. In a series of proof-of-principle experiments, we detect weakly bound dimers via three-photon ionization with femtosecond pulses (τ = 30 fs) at a central wavelength of 780 nm and measure directly the momenta of the photoelectrons in coincidence with recoil ions.
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Stark J, Warnecke C, Bogen S, Chen S, Dijck EA, Kühn S, Rosner MK, Graf A, Nauta J, Oelmann JH, Schmöger L, Schwarz M, Liebert D, Spieß LJ, King SA, Leopold T, Micke P, Schmidt PO, Pfeifer T, Crespo López-Urrutia JR. An ultralow-noise superconducting radio-frequency ion trap for frequency metrology with highly charged ions. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:083203. [PMID: 34470420 DOI: 10.1063/5.0046569] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2021] [Accepted: 07/13/2021] [Indexed: 06/13/2023]
Abstract
We present a novel ultrastable superconducting radio-frequency (RF) ion trap realized as a combination of an RF cavity and a linear Paul trap. Its RF quadrupole mode at 34.52 MHz reaches a quality factor of Q ≈ 2.3 × 105 at a temperature of 4.1 K and is used to radially confine ions in an ultralow-noise pseudopotential. This concept is expected to strongly suppress motional heating rates and related frequency shifts that limit the ultimate accuracy achieved in advanced ion traps for frequency metrology. Running with its low-vibration cryogenic cooling system, electron-beam ion trap, and deceleration beamline supplying highly charged ions (HCIs), the superconducting trap offers ideal conditions for optical frequency metrology with ionic species. We report its proof-of-principle operation as a quadrupole-mass filter with HCIs and trapping of Doppler-cooled 9Be+ Coulomb crystals.
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Belsa B, Amini K, Liu X, Sanchez A, Steinle T, Steinmetzer J, Le AT, Moshammer R, Pfeifer T, Ullrich J, Moszynski R, Lin CD, Gräfe S, Biegert J. Erratum: Publisher's Note: "Laser-induced electron diffraction of the ultrafast umbrella motion in ammonia" [Struct. Dyn. 8, 014301 (2021)]. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2021; 8:049901. [PMID: 34497865 PMCID: PMC8410134 DOI: 10.1063/4.0000117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Indexed: 06/13/2023]
Abstract
[This corrects the article DOI: 10.1063/4.0000046.].
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Sanchez A, Amini K, Wang SJ, Steinle T, Belsa B, Danek J, Le AT, Liu X, Moshammer R, Pfeifer T, Richter M, Ullrich J, Gräfe S, Lin CD, Biegert J. Molecular structure retrieval directly from laboratory-frame photoelectron spectra in laser-induced electron diffraction. Nat Commun 2021; 12:1520. [PMID: 33750798 PMCID: PMC7943781 DOI: 10.1038/s41467-021-21855-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Accepted: 02/17/2021] [Indexed: 01/31/2023] Open
Abstract
Ubiquitous to most molecular scattering methods is the challenge to retrieve bond distance and angle from the scattering signals since this requires convergence of pattern matching algorithms or fitting methods. This problem is typically exacerbated when imaging larger molecules or for dynamic systems with little a priori knowledge. Here, we employ laser-induced electron diffraction (LIED) which is a powerful means to determine the precise atomic configuration of an isolated gas-phase molecule with picometre spatial and attosecond temporal precision. We introduce a simple molecular retrieval method, which is based only on the identification of critical points in the oscillating molecular interference scattering signal that is extracted directly from the laboratory-frame photoelectron spectrum. The method is compared with a Fourier-based retrieval method, and we show that both methods correctly retrieve the asymmetrically stretched and bent field-dressed configuration of the asymmetric top molecule carbonyl sulfide (OCS), which is confirmed by our quantum-classical calculations.
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Nauta J, Oelmann JH, Borodin A, Ackermann A, Knauer P, Muhammad IS, Pappenberger R, Pfeifer T, Crespo López-Urrutia JR. XUV frequency comb production with an astigmatism-compensated enhancement cavity. OPTICS EXPRESS 2021; 29:2624-2636. [PMID: 33726454 DOI: 10.1364/oe.414987] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Accepted: 12/21/2020] [Indexed: 06/12/2023]
Abstract
We have developed an extreme ultraviolet (XUV) frequency comb for performing ultra-high precision spectroscopy on the many XUV transitions found in highly charged ions (HCI). Femtosecond pulses from a 100 MHz phase-stabilized near-infrared frequency comb are amplified and then fed into a femtosecond enhancement cavity (fsEC) inside an ultra-high vacuum chamber. The low-dispersion fsEC coherently superposes several hundred incident pulses and, with a single cylindrical optical element, fully compensates astigmatism at the w0 = 15 µm waist cavity focus. With a gas jet installed there, intensities reaching ∼ 1014 W/cm2 generate coherent high harmonics with a comb spectrum at 100 MHz rate. We couple out of the fsEC harmonics from the 7th up to the 35th (42 eV; 30 nm) to be used in upcoming experiments on HCI frequency metrology.
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Belsa B, Amini K, Liu X, Sanchez A, Steinle T, Steinmetzer J, Le AT, Moshammer R, Pfeifer T, Ullrich J, Moszynski R, Lin CD, Gräfe S, Biegert J. Laser-induced electron diffraction of the ultrafast umbrella motion in ammonia. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2021; 8:014301. [PMID: 34026922 PMCID: PMC8121549 DOI: 10.1063/4.0000046] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Accepted: 12/25/2020] [Indexed: 06/12/2023]
Abstract
Visualizing molecular transformations in real-time requires a structural retrieval method with Ångström spatial and femtosecond temporal atomic resolution. Imaging of hydrogen-containing molecules additionally requires an imaging method sensitive to the atomic positions of hydrogen nuclei, with most methods possessing relatively low sensitivity to hydrogen scattering. Laser-induced electron diffraction (LIED) is a table-top technique that can image ultrafast structural changes of gas-phase polyatomic molecules with sub-Ångström and femtosecond spatiotemporal resolution together with relatively high sensitivity to hydrogen scattering. Here, we image the umbrella motion of an isolated ammonia molecule (NH3) following its strong-field ionization. Upon ionization of a neutral ammonia molecule, the ammonia cation (NH3 +) undergoes an ultrafast geometrical transformation from a pyramidal ( Φ HNH = 107 ° ) to planar ( Φ HNH = 120 ° ) structure in approximately 8 femtoseconds. Using LIED, we retrieve a near-planar ( Φ HNH = 117 ± 5 ° ) field-dressed NH3 + molecular structure 7.8 - 9.8 femtoseconds after ionization. Our measured field-dressed NH3 + structure is in excellent agreement with our calculated equilibrium field-dressed structure using quantum chemical ab initio calculations.
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Leutenegger MA, Kühn S, Micke P, Steinbrügge R, Stierhof J, Shah C, Hell N, Bissinger M, Hirsch M, Ballhausen R, Lang M, Gräfe C, Wipf S, Cumbee R, Betancourt-Martinez GL, Park S, Yerokhin VA, Surzhykov A, Stolte WC, Niskanen J, Chung M, Porter FS, Stöhlker T, Pfeifer T, Wilms J, Brown GV, Crespo López-Urrutia JR, Bernitt S. High-Precision Determination of Oxygen K_{α} Transition Energy Excludes Incongruent Motion of Interstellar Oxygen. PHYSICAL REVIEW LETTERS 2020; 125:243001. [PMID: 33412031 DOI: 10.1103/physrevlett.125.243001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Revised: 10/19/2020] [Accepted: 10/30/2020] [Indexed: 06/12/2023]
Abstract
We demonstrate a widely applicable technique to absolutely calibrate the energy scale of x-ray spectra with experimentally well-known and accurately calculable transitions of highly charged ions, allowing us to measure the K-shell Rydberg spectrum of molecular O_{2} with 8 meV uncertainty. We reveal a systematic ∼450 meV shift from previous literature values, and settle an extraordinary discrepancy between astrophysical and laboratory measurements of neutral atomic oxygen, the latter being calibrated against the aforementioned O_{2} literature values. Because of the widespread use of such, now deprecated, references, our method impacts on many branches of x-ray absorption spectroscopy. Moreover, it potentially reduces absolute uncertainties there to below the meV level.
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Nauta J, Oelmann JH, Ackermann A, Knauer P, Pappenberger R, Borodin A, Muhammad IS, Ledwa H, Pfeifer T, Crespo López-Urrutia JR. 100 MHz frequency comb for low-intensity multi-photon studies: intra-cavity velocity-map imaging of xenon. OPTICS LETTERS 2020; 45:2156-2159. [PMID: 32287180 DOI: 10.1364/ol.389327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2020] [Accepted: 03/06/2020] [Indexed: 06/11/2023]
Abstract
We raise the power from a commercial 10 W frequency comb inside an enhancement cavity and perform multi-photon ionization of gas-phase atoms at 100 MHz for the first time, to the best of our knowledge. An intra-cavity velocity-map-imaging setup collects electron-energy spectra of xenon at rates several orders of magnitude higher than those of conventional laser systems. Consequently, we can use much lower intensities ${\sim}{{10}^{12}} \;{\rm W}/{{\rm cm}^2} $∼1012W/cm2 without increasing acquisition times above just a few seconds. The high rate and coherence of the stabilized femtosecond pulses are known to be transferred to the actively stabilized cavity and will allow studying purely perturbative multi-photon effects, paving the road towards a new field of precision tests in nonlinear physics.
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Ben Ltaief L, Shcherbinin M, Mandal S, Krishnan SR, Richter R, Pfeifer T, Bauer M, Ghosh A, Mudrich M, Gokhberg K, LaForge AC. Electron transfer mediated decay of alkali dimers attached to He nanodroplets. Phys Chem Chem Phys 2020; 22:8557-8564. [DOI: 10.1039/d0cp00256a] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Double ionization of alkali dimers attached to He nanodroplets by electron transfer mediated decay (ETMD).
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Ben Ltaief L, Shcherbinin M, Mandal S, Krishnan SR, LaForge AC, Richter R, Turchini S, Zema N, Pfeifer T, Fasshauer E, Sisourat N, Mudrich M. Charge Exchange Dominates Long-Range Interatomic Coulombic Decay of Excited Metal-Doped Helium Nanodroplets. J Phys Chem Lett 2019; 10:6904-6909. [PMID: 31625747 DOI: 10.1021/acs.jpclett.9b02726] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Atoms and molecules attached to rare-gas clusters are ionized by an interatomic autoionization process traditionally termed "Penning ionization" when the host cluster is resonantly excited. Here we analyze this process in the light of the interatomic Coulombic decay (ICD) mechanism, which usually contains a contribution from charge exchange at a short interatomic distance and one from virtual photon transfer at a large interatomic distance. For helium (He) nanodroplets doped with alkali metal atoms (Li, Rb), we show that long-range and short-range contributions to the interatomic autoionization can be clearly distinguished by detecting electrons and ions in coincidence. Surprisingly, ab initio calculations show that even for alkali metal atoms floating in dimples at a large distance from the nanodroplet surface, autoionization is largely dominated by charge-exchange ICD. Furthermore, the measured electron spectra manifest the ultrafast internal relaxation of the droplet mainly into the 1s2s1S state and partially into the metastable 1s2s3S state.
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Micke P, Stark J, King SA, Leopold T, Pfeifer T, Schmöger L, Schwarz M, Spieß LJ, Schmidt PO, Crespo López-Urrutia JR. Closed-cycle, low-vibration 4 K cryostat for ion traps and other applications. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2019; 90:065104. [PMID: 31254988 DOI: 10.1063/1.5088593] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Accepted: 05/15/2019] [Indexed: 06/09/2023]
Abstract
In vacuo cryogenic environments are ideal for applications requiring both low temperatures and extremely low particle densities. This enables reaching long storage and coherence times, for example, in ion traps, essential requirements for experiments with highly charged ions, quantum computation, and optical clocks. We have developed a novel cryostat continuously refrigerated with a pulse-tube cryocooler and providing the lowest vibration level reported for such a closed-cycle system with 1 W cooling power for a <5 K experiment. A decoupling system suppresses vibrations from the cryocooler by three orders of magnitude down to a level of 10 nm peak amplitudes in the horizontal plane. Heat loads of about 40 W (at 45 K) and 1 W (at 4 K) are transferred from an experimental chamber, mounted on an optical table, to the cryocooler through a vacuum-insulated massive 120 kg inertial copper pendulum. The 1.4 m long pendulum allows installation of the cryocooler in a separate, acoustically isolated machine room. At the experimental chamber, we measured the residual vibrations using an interferometric setup. The positioning of the 4 K elements is reproduced to better than a few micrometer after a full thermal cycle to room temperature. Extreme high vacuum on the 10-15 mbar level is achieved. In collaboration with the Max-Planck-Institut für Kernphysik, such a setup is now in operation at the Physikalisch-Technische Bundesanstalt for a next-generation optical clock experiment using highly charged ions.
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Shcherbinin M, Westergaard FV, Hanif M, Krishnan SR, LaForge AC, Richter R, Pfeifer T, Mudrich M. Inelastic scattering of photoelectrons from He nanodroplets. J Chem Phys 2019; 150:044304. [PMID: 30709284 DOI: 10.1063/1.5074130] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
We present a detailed study of inelastic energy-loss collisions of photoelectrons emitted from He nanodroplets by tunable extreme ultraviolet (XUV) radiation. Using coincidence imaging detection of electrons and ions, we probe the lowest He droplet excited states up to the electron impact ionization threshold. We find significant signal contributions from photoelectrons emitted from free He atoms accompanying the He nanodroplet beam. Furthermore, signal contributions from photoionization and electron impact excitation/ionization occurring in pairs of nearest-neighbor atoms in the He droplets are detected. This work highlights the importance of inelastic electron scattering in the interaction of nanoparticles with XUV radiation.
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20
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Stooß V, Cavaletto SM, Donsa S, Blättermann A, Birk P, Keitel CH, Březinová I, Burgdörfer J, Ott C, Pfeifer T. Real-Time Reconstruction of the Strong-Field-Driven Dipole Response. PHYSICAL REVIEW LETTERS 2018; 121:173005. [PMID: 30411962 DOI: 10.1103/physrevlett.121.173005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Indexed: 06/08/2023]
Abstract
The reconstruction of the full temporal dipole response of a strongly driven time-dependent system from a single absorption spectrum is demonstrated, only requiring that a sufficiently short pulse is employed to initialize the coherent excitation of the system. We apply this finding to the time-domain observation of Rabi cycling between doubly excited atomic states in the few-femtosecond regime. This allows us to pinpoint the breakdown of few-level quantum dynamics at the critical laser intensity near 2 TW/cm^{2} in doubly excited helium. The present approach unlocks single-shot real-time-resolved signal reconstruction across timescales down to attoseconds for nonequilibrium states of matter. In contrast to conventional pump-probe schemes, there is no need for scanning time delays in order to access real-time information. The potential future applications of this technique range from testing fundamental quantum dynamics in strong fields to measuring and controlling ultrafast chemical and biological reaction processes when applied to traditional transient-absorption spectroscopy.
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Micke P, Kühn S, Buchauer L, Harries JR, Bücking TM, Blaum K, Cieluch A, Egl A, Hollain D, Kraemer S, Pfeifer T, Schmidt PO, Schüssler RX, Schweiger C, Stöhlker T, Sturm S, Wolf RN, Bernitt S, Crespo López-Urrutia JR. The Heidelberg compact electron beam ion traps. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:063109. [PMID: 29960545 DOI: 10.1063/1.5026961] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Electron beam ion traps (EBITs) are ideal tools for both production and study of highly charged ions (HCIs). In order to reduce their construction, maintenance, and operation costs, we have developed a novel, compact, room-temperature design, the Heidelberg Compact EBIT (HC-EBIT). Four already commissioned devices operate at the strongest fields (up to 0.86 T) reported for such EBITs using permanent magnets, run electron beam currents up to 80 mA, and energies up to 10 keV. They demonstrate HCI production, trapping, and extraction of pulsed Ar16+ bunches and continuous 100 pA ion beams of highly charged Xe up to charge state 29+, already with a 4 mA, 2 keV electron beam. Moreover, HC-EBITs offer large solid-angle ports and thus high photon count rates, e.g., in x-ray spectroscopy of dielectronic recombination in HCIs up to Fe24+, achieving an electron-energy resolving power of E/ΔE > 1500 at 5 keV. Besides traditional on-axis electron guns, we have also implemented a novel off-axis gun for laser, synchrotron, and free-electron laser applications, offering clear optical access along the trap axis. We report on its first operation at a synchrotron radiation facility demonstrating the resonant photoexcitation of highly charged oxygen.
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22
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Blessenohl MA, Dobrodey S, Warnecke C, Rosner MK, Graham L, Paul S, Baumann TM, Hockenbery Z, Hubele R, Pfeifer T, Ames F, Dilling J, Crespo López-Urrutia JR. An electron beam ion trap and source for re-acceleration of rare-isotope ion beams at TRIUMF. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:052401. [PMID: 29864823 DOI: 10.1063/1.5021045] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Electron beam driven ionization can produce highly charged ions (HCIs) in a few well-defined charge states. Ideal conditions for this are maximally focused electron beams and an extremely clean vacuum environment. A cryogenic electron beam ion trap fulfills these prerequisites and delivers very pure HCI beams. The Canadian rare isotope facility with electron beam ion source-electron beam ion sources developed at the Max-Planck-Institut für Kernphysik (MPIK) reaches already for a 5 keV electron beam and a current of 1 A with a density in excess of 5000 A/cm2 by means of a 6 T axial magnetic field. Within the trap, the beam quickly generates a dense HCI population, tightly confined by a space-charge potential of the order of 1 keV times the ionic charge state. Emitting HCI bunches of ≈107 ions at up to 100 Hz repetition rate, the device will charge-breed rare-isotope beams with the mass-over-charge ratio required for re-acceleration at the Advanced Rare IsotopE Laboratory (ARIEL) facility at TRIUMF. We present here its design and results from commissioning runs at MPIK, including X-ray diagnostics of the electron beam and charge-breeding process, as well as ion injection and HCI-extraction measurements.
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23
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Heeg KP, Kaldun A, Strohm C, Reiser P, Ott C, Subramanian R, Lentrodt D, Haber J, Wille HC, Goerttler S, Rüffer R, Keitel CH, Röhlsberger R, Pfeifer T, Evers J. Spectral narrowing of x-ray pulses for precision spectroscopy with nuclear resonances. Science 2017; 357:375-378. [PMID: 28751603 DOI: 10.1126/science.aan3512] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Accepted: 06/26/2017] [Indexed: 11/02/2022]
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24
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Kaldun A, Blättermann A, Stooß V, Donsa S, Wei H, Pazourek R, Nagele S, Ott C, Lin CD, Burgdörfer J, Pfeifer T. Observing the ultrafast buildup of a Fano resonance in the time domain. Science 2017; 354:738-741. [PMID: 27846603 DOI: 10.1126/science.aah6972] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Accepted: 09/30/2016] [Indexed: 11/02/2022]
Abstract
Although the time-dependent buildup of asymmetric Fano line shapes in absorption spectra has been of great theoretical interest in the past decade, experimental verification of the predictions has been elusive. Here, we report the experimental observation of the emergence of a Fano resonance in the prototype system of helium by interrupting the autoionization process of a correlated two-electron excited state with a strong laser field. The tunable temporal gate between excitation and termination of the resonance allows us to follow the formation of a Fano line shape in time. The agreement with ab initio calculations validates our experimental time-gating technique for addressing an even broader range of topics, such as the emergence of electron correlation, the onset of electron-internuclear coupling, and quasi-particle formation.
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25
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Wolter B, Pullen MG, Le AT, Baudisch M, Doblhoff-Dier K, Senftleben A, Hemmer M, Schröter CD, Ullrich J, Pfeifer T, Moshammer R, Gräfe S, Vendrell O, Lin CD, Biegert J. Ultrafast electron diffraction imaging of bond breaking in di-ionized acetylene. Science 2017; 354:308-312. [PMID: 27846561 DOI: 10.1126/science.aah3429] [Citation(s) in RCA: 106] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Accepted: 09/19/2016] [Indexed: 01/27/2023]
Abstract
Visualizing chemical reactions as they occur requires atomic spatial and femtosecond temporal resolution. Here, we report imaging of the molecular structure of acetylene (C2H2) 9 femtoseconds after ionization. Using mid-infrared laser-induced electron diffraction (LIED), we obtained snapshots as a proton departs the [C2H2]2+ ion. By introducing an additional laser field, we also demonstrate control over the ultrafast dissociation process and resolve different bond dynamics for molecules oriented parallel versus perpendicular to the LIED field. These measurements are in excellent agreement with a quantum chemical description of field-dressed molecular dynamics.
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