1
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Tran S, Tran KC, Saenz Rodriguez A, Kong W. Kinetic energy distributions of atomic ions from disintegration of argon containing nanoclusters in moderately intense nanosecond laser fields: Coulomb explosion or hydrodynamic expansion. Phys Chem Chem Phys 2024; 26:8631-8640. [PMID: 38436420 DOI: 10.1039/d3cp05894h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/05/2024]
Abstract
We report kinetic energies (KE) of multiply charged atomic ions (MCAI) from interactions of moderately intense nanosecond lasers at 532 nm with argon containing clusters, including neat and doped clusters with a trace amount of trichlorobenzene. We develop a mathematical method to retrieve speed and thereby kinetic energy information from analyzing the time-of-flight profiles of the MCAI. This method should be generally applicable in detections of energetic charged particles with high velocities, a realm where velocity map imaging is inadequate. From this analysis, we discover that the KE of MCAI from doped clusters demonstrates a quadratic dependence on the charge of the atomic ions, while for neat clusters, the dependence is cubic. This result confirms the nature of the cluster disintegration process to be dominated by Coulomb explosion. This result bears more similarity to reports from extreme vacuum ultraviolet (EUV) fields with similar intensities, than to reports from near infrared (NIR) intense laser fields. However, the charge state distribution from our experiment is the opposite: we observe more higher charge state ions than reported in EUV fields, and our charge state distribution is actually similar to those reported in NIR fields. We also report a significant effect of the external electric field on the charge state distribution of the atomic ions: the presence of an electric field can significantly increase the charge from the atomic ions, as shown by a three-fold reduction in the average kinetic energy per charge. Although molecular dynamics simulations have been implemented for experiments in the EUV and NIR, our results allude to the need of a concerted effort in this regime of moderately intense nanosecond laser fields. The significant decrease in charge state distribution and the significant increase in KE from doped clusters, compared with neat clusters, is a telltale sign that the true interaction time between the laser field and the cluster may be substantially shorter than the duration of the laser, a welcome relief for molecular dynamics simulations.
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Affiliation(s)
- Steven Tran
- Department of Chemistry, Oregon State University, Corvallis, Oregon, 97331, USA.
| | - Kim C Tran
- Department of Chemistry, Oregon State University, Corvallis, Oregon, 97331, USA.
| | - Axel Saenz Rodriguez
- Department of Mathematics, Oregon State University, Corvallis, Oregon, 97331, USA
| | - Wei Kong
- Department of Chemistry, Oregon State University, Corvallis, Oregon, 97331, USA.
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2
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Bacellar C, Chatterley AS, Lackner F, Pemmaraju CD, Tanyag RMP, Verma D, Bernando C, O'Connell SMO, Bucher M, Ferguson KR, Gorkhover T, Coffee RN, Coslovich G, Ray D, Osipov T, Neumark DM, Bostedt C, Vilesov AF, Gessner O. Anisotropic Surface Broadening and Core Depletion during the Evolution of a Strong-Field Induced Nanoplasma. PHYSICAL REVIEW LETTERS 2022; 129:073201. [PMID: 36018694 DOI: 10.1103/physrevlett.129.073201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Revised: 04/30/2022] [Accepted: 06/29/2022] [Indexed: 06/15/2023]
Abstract
Strong-field ionization of nanoscale clusters provides excellent opportunities to study the complex correlated electronic and nuclear dynamics of near-solid density plasmas. Yet, monitoring ultrafast, nanoscopic dynamics in real-time is challenging, which often complicates a direct comparison between theory and experiment. Here, near-infrared laser-induced plasma dynamics in ∼600 nm diameter helium droplets are studied by femtosecond time-resolved x-ray coherent diffractive imaging. An anisotropic, ∼20 nm wide surface region, defined as the range where the density lies between 10% and 90% of the core value, is established within ∼100 fs, in qualitative agreement with theoretical predictions. At longer timescales, however, the width of this region remains largely constant while the radius of the dense plasma core shrinks at average rates of ≈71 nm/ps along and ≈33 nm/ps perpendicular to the laser polarization. These dynamics are not captured by previous plasma expansion models. The observations are phenomenologically described within a numerical simulation; details of the underlying physics, however, remain to be explored.
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Affiliation(s)
- Camila Bacellar
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Chemistry, University of California Berkeley, Berkeley, California 94720, USA
| | - Adam S Chatterley
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Chemistry, University of California Berkeley, Berkeley, California 94720, USA
| | - Florian Lackner
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Chemistry, University of California Berkeley, Berkeley, California 94720, USA
| | - C D Pemmaraju
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Rico Mayro P Tanyag
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
| | - Deepak Verma
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
| | - Charles Bernando
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, USA
| | - Sean M O O'Connell
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
| | - Maximilian Bucher
- Argonne National Laboratory, 9700 South Cass Avenue B109, Lemont, Illinois 60439, USA
| | - Ken R Ferguson
- Linac Coherent Light Source, LCLS, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Tais Gorkhover
- Linac Coherent Light Source, LCLS, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
- Institute of Optics and Atomic Physics, Technical University of Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Ryan N Coffee
- Linac Coherent Light Source, LCLS, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Giacomo Coslovich
- Linac Coherent Light Source, LCLS, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Dipanwita Ray
- Linac Coherent Light Source, LCLS, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Timur Osipov
- Linac Coherent Light Source, LCLS, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
| | - Daniel M Neumark
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
- Department of Chemistry, University of California Berkeley, Berkeley, California 94720, USA
| | - Christoph Bostedt
- Argonne National Laboratory, 9700 South Cass Avenue B109, Lemont, Illinois 60439, USA
- Linac Coherent Light Source, LCLS, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA
- Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA
| | - Andrey F Vilesov
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California 90089, USA
| | - Oliver Gessner
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
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3
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Yao Y, Zhang J, Pandey R, Wu D, Kong W, Xue L. Intensity dependence of multiply charged atomic ions from argon clusters in moderate nanosecond laser fields. J Chem Phys 2021; 155:144301. [PMID: 34654315 DOI: 10.1063/5.0065086] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
We report the laser intensity dependence of multiply charged atomic ions (MCAIs) Arn+ with 2 ≤ n ≤ 8 from argon clusters in focused nanosecond laser fields at 532 nm. The laser field, in the range of 1011-1012 W/cm2, is insufficient for optical field ionization but is adequate for multiphoton ionization. The MCAI sections of the mass spectra for clusters containing 3700 and 26 000 atoms are dominated by Arn+ with 7 ≤ n ≤ 9, extending to Ar14+. While the distributions of the MCAIs remain largely constant throughout the intensity range of the laser, the abundance of Ar+ relative to the abundances of the MCAIs increases dramatically with increasing laser intensity. Consequently, exponential fittings of the yields result in a larger exponent for Ar+ than for MCAIs, and the exponents of MCAIs with 2 ≤ n ≤ 8 are similar, with only slight variations for different charge states. The width of the arrival time and, hence, the corresponding kinetic energy of Ar+ also increases with increasing laser intensities, while the width of the arrival time of MCAIs remains constant throughout the range of measurements. These results call for more detailed theoretical investigations in this regime of laser-matter interactions.
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Affiliation(s)
- Yuzhong Yao
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA
| | - Jie Zhang
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA
| | - Rahul Pandey
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA
| | - Di Wu
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA
| | - Wei Kong
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, USA
| | - Lan Xue
- Department of Statistics, Oregon State University, Corvallis, Oregon 97331, USA
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4
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Yao Y, Freund WM, Zhang J, Kong W. Volume averaging effect in nonlinear processes of focused laser fields. J Chem Phys 2021; 155:064202. [PMID: 34391368 DOI: 10.1063/5.0061038] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
We report theoretical derivations and experimental results on the volume averaging effect of nonlinear processes in focused laser fields. This effect is considered detrimental in revealing the intensity dependence of a nonlinear process, caused by the intensity variation across the sampled volume of a focused laser. Following the treatment in the literature, we prove that if the signal dependence can be expressed as a simple power function of the laser intensity and if the detection region encompasses effectively the whole volume, volume average does not affect the final conclusion on the derived exponent. However, to reveal the detailed saturation effect of a multi-photon process, intensity selective scans involving spatial filters and displacement of the laser focus (z-scan) are required. Moreover, to fully capture the dependence of the signal on the variation of the laser intensity, the degree of spatial discrimination and the corresponding range of the z-scan need to be modeled carefully. Limitations in the dynamic range of the detector or the laser power, however, can thwart the desired scan range, resulting in erroneous fitting exponents. Using our nanosecond laser with a non-ideal Gaussian beam profile based on multiphoton ionization of argon atoms from a collimated molecular beam and from ambient argon gas, we report experimental measurements of the beam waist and Rayleigh range and compare the experimental intensity dependence of Ar+ with theoretical values. Agreements between theory and experiment are remarkable.
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Affiliation(s)
- Yuzhong Yao
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, USA
| | - William M Freund
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, USA
| | - Jie Zhang
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, USA
| | - Wei Kong
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331-4003, USA
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Yao Y, Zhang J, Pandey R, Kong W. Production of Multiply Charged Argon Ions in Moderate Nanosecond Laser Fields: An Open Question or a Forgone Conclusion? J Phys Chem Lett 2020; 11:9971-9974. [PMID: 33207881 PMCID: PMC8009038 DOI: 10.1021/acs.jpclett.0c02948] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We reply to the Viewpoint by Vatsa and Mathur on our publication reporting the observation of multiply charged atomic ions from argon clusters doped with aromatic chromophores in a moderate nanosecond laser field. Vatsa and Mathur raised three concerns about the proposed explanation and offered additional ideas for the reported process. We agree with some of their concerns and welcome the addition of information, and we also clarify a few misunderstandings of our intention, perhaps caused by our implicit assumption of contextual relations. While the experimental results are indisputable, the interpretation is still a topic of debate, subject to further experimental investigations and theoretical modeling.
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Affiliation(s)
- Yuzhong Yao
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, United States
| | - Jie Zhang
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, United States
| | - Rahul Pandey
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, United States
| | - Wei Kong
- Department of Chemistry, Oregon State University, Corvallis, Oregon 97331, United States
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Vatsa RK, Mathur D. Generation of Multiply Charged Argon Ions in Nanosecond Laser Field Ionization of Argon Clusters. J Phys Chem Lett 2020; 11:9842-9845. [PMID: 33207882 DOI: 10.1021/acs.jpclett.0c02223] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Zhang and co-workers ( J. Phys. Chem. Lett. 2020, 11, 1100-1105) have recently reported results of experiments involving irradiation of argon clusters doped with bromofluorene chromophores by nanosecond-long pulses of 532 nm laser light. Multiply charged ions of atomic argon (Arn+, 1 ≤ n ≤ 7) and carbon (Cn+, 1 ≤ n ≤ 4) are observed, which are sought to be rationalized using an evaporation model. The distinguishing facet of exploding clusters being progenitors of energetic ions and electrons constitutes the key driver for contemporary research in laser-cluster interactions; it is, therefore, important to point out inconsistencies that are intrinsic to the model of Zhang and co-workers. In light of similar reports already in the literature, we show that their model is of limited utility in describing the dynamics that govern how fast, multiply charged atomic ions result from laser irradiation of gas-phase clusters. We posit that it is plasma behavior that underpins cluster heating and cluster explosion dynamics.
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Affiliation(s)
- Rajesh K Vatsa
- Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India
| | - Deepak Mathur
- Department of Atomic and Molecular Physics, Manipal Academy of Higher Education, Manipal 576 104, India
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7
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Rupp D, Flückiger L, Adolph M, Colombo A, Gorkhover T, Harmand M, Krikunova M, Müller JP, Oelze T, Ovcharenko Y, Richter M, Sauppe M, Schorb S, Treusch R, Wolter D, Bostedt C, Möller T. Imaging plasma formation in isolated nanoparticles with ultrafast resonant scattering. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2020; 7:034303. [PMID: 32596413 PMCID: PMC7304997 DOI: 10.1063/4.0000006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Accepted: 05/13/2020] [Indexed: 06/11/2023]
Abstract
We have recorded the diffraction patterns from individual xenon clusters irradiated with intense extreme ultraviolet pulses to investigate the influence of light-induced electronic changes on the scattering response. The clusters were irradiated with short wavelength pulses in the wavelength regime of different 4d inner-shell resonances of neutral and ionic xenon, resulting in distinctly different optical properties from areas in the clusters with lower or higher charge states. The data show the emergence of a transient structure with a spatial extension of tens of nanometers within the otherwise homogeneous sample. Simulations indicate that ionization and nanoplasma formation result in a light-induced outer shell in the cluster with a strongly altered refractive index. The presented resonant scattering approach enables imaging of ultrafast electron dynamics on their natural timescale.
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Affiliation(s)
- Daniela Rupp
- Authors to whom correspondence should be addressed: and
| | | | - Marcus Adolph
- IOAP, Technische Universität Berlin, 10623 Berlin, Germany
| | | | - Tais Gorkhover
- Stanford PULSE Institute, SLAC National Laboratory, Menlo Park, California 94305, USA
| | | | | | | | - Tim Oelze
- IOAP, Technische Universität Berlin, 10623 Berlin, Germany
| | | | - Maria Richter
- IOAP, Technische Universität Berlin, 10623 Berlin, Germany
| | | | | | | | | | | | - Thomas Möller
- IOAP, Technische Universität Berlin, 10623 Berlin, Germany
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8
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The Role of Electron Trajectories in XUV-Initiated High-Harmonic Generation. APPLIED SCIENCES-BASEL 2019. [DOI: 10.3390/app9030378] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
High-harmonic generation spectroscopy is a powerful tool for ultrafast spectroscopy with intrinsic attosecond time resolution. Its major limitation—the fact that a strong infrared driving pulse is governing the entire generation process—is lifted by extreme ultraviolet (XUV)-initiated high-harmonic generation (HHG). Tunneling ionization is replaced by XUV photoionization, which decouples ionization from recollision. Here we probe the intensity dependence of XUV-initiated HHG and observe strong spectral frequency shifts of the high harmonics. We are able to tune the shift by controlling the instantaneous intensity of the infrared field. We directly access the reciprocal intensity parameter associated with the electron trajectories and identify short and long trajectories. Our findings are supported and analyzed by ab initio calculations and a semiclassical trajectory model. The ability to isolate and control long trajectories in XUV-initiated HHG increases the range of the intrinsic attosecond clock for spectroscopic applications.
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9
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Schütte B, Ye P, Patchkovskii S, Austin DR, Brahms C, Strüber C, Witting T, Ivanov MY, Tisch JWG, Marangos JP. Strong-field ionization of clusters using two-cycle pulses at 1.8 μm. Sci Rep 2016; 6:39664. [PMID: 28009012 PMCID: PMC5180105 DOI: 10.1038/srep39664] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2016] [Accepted: 11/24/2016] [Indexed: 11/23/2022] Open
Abstract
The interaction of intense laser pulses with nanoscale particles leads to the production of high-energy electrons, ions, neutral atoms, neutrons and photons. Up to now, investigations have focused on near-infrared to X-ray laser pulses consisting of many optical cycles. Here we study strong-field ionization of rare-gas clusters (103 to 105 atoms) using two-cycle 1.8 μm laser pulses to access a new interaction regime in the limit where the electron dynamics are dominated by the laser field and the cluster atoms do not have time to move significantly. The emission of fast electrons with kinetic energies exceeding 3 keV is observed using laser pulses with a wavelength of 1.8 μm and an intensity of 1 × 1015 W/cm2, whereas only electrons below 500 eV are observed at 800 nm using a similar intensity and pulse duration. Fast electrons are preferentially emitted along the laser polarization direction, showing that they are driven out from the cluster by the laser field. In addition to direct electron emission, an electron rescattering plateau is observed. Scaling to even longer wavelengths is expected to result in a highly directional current of energetic electrons on a few-femtosecond timescale.
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Affiliation(s)
- Bernd Schütte
- Department of Physics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
| | - Peng Ye
- Department of Physics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
| | | | - Dane R. Austin
- Department of Physics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
| | - Christian Brahms
- Department of Physics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
| | - Christian Strüber
- Department of Physics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
| | - Tobias Witting
- Department of Physics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
| | - Misha Yu. Ivanov
- Department of Physics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
- Max-Born-Institut, Max-Born-Strasse 2A, 12489 Berlin, Germany
| | - John W. G. Tisch
- Department of Physics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
| | - Jon P. Marangos
- Department of Physics, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
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Li H, Mignolet B, Wang Z, Betsch KJ, Carnes KD, Ben-Itzhak I, Cocke CL, Remacle F, Kling MF. Transition from SAMO to Rydberg State Ionization in C 60 in Femtosecond Laser Fields. J Phys Chem Lett 2016; 7:4677-4682. [PMID: 27934203 PMCID: PMC5190148 DOI: 10.1021/acs.jpclett.6b02139] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2016] [Accepted: 11/02/2016] [Indexed: 05/20/2023]
Abstract
The transition between two distinct ionization mechanisms in femtosecond laser fields at 785 nm is observed for C60 molecules. The transition occurs in the investigated intensity range from 3 to 20 TW/cm2 and is visualized in electron kinetic energy spectra below the one-photon energy (1.5 eV) obtained via velocity map imaging. Assignment of several observed broad spectral peaks to ionization from superatom molecular orbitals (SAMOs) and Rydberg states is based on time-dependent density functional theory simulations. We find that ionization from SAMOs dominates the spectra for intensities below 5 TW/cm2. As the intensity increases, Rydberg state ionization exceeds the prominence of SAMOs. Using short laser pulses (20 fs) allowed uncovering of distinct six-lobe photoelectron angular distributions with kinetic energies just above the threshold (below 0.2 eV), which we interpret as over-the-barrier ionization of shallow f-Rydberg states in C60.
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Affiliation(s)
- H. Li
- J. R. Macdonald
Laboratory, Physics Department, Kansas State University, Manhattan, Kansas 66506, United States
- State
Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
| | - B. Mignolet
- Department
of Chemistry, University of Liege, B-4000 Liege, Belgium
| | - Z. Wang
- J. R. Macdonald
Laboratory, Physics Department, Kansas State University, Manhattan, Kansas 66506, United States
- The MOE Key Laboratory
of Weak-Light Nonlinear Photonics, TEDA Applied Physics
Institute and School of Physics, Nankai
University, Tianjin 300457, China
| | - K. J. Betsch
- J. R. Macdonald
Laboratory, Physics Department, Kansas State University, Manhattan, Kansas 66506, United States
| | - K. D. Carnes
- J. R. Macdonald
Laboratory, Physics Department, Kansas State University, Manhattan, Kansas 66506, United States
| | - I. Ben-Itzhak
- J. R. Macdonald
Laboratory, Physics Department, Kansas State University, Manhattan, Kansas 66506, United States
| | - C. L. Cocke
- J. R. Macdonald
Laboratory, Physics Department, Kansas State University, Manhattan, Kansas 66506, United States
| | - F. Remacle
- Department
of Chemistry, University of Liege, B-4000 Liege, Belgium
- E-mail: (F.R.)
| | - M. F. Kling
- J. R. Macdonald
Laboratory, Physics Department, Kansas State University, Manhattan, Kansas 66506, United States
- Department
of Physics, Ludwig-Maximilians-Universität
Munich, D-85748 Garching, Germany
- E-mail: (M.F.K.)
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