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Disentangling the Effect of Ionic Coupling and Multiple Interfering Terms in Attosecond Molecular Interferometry
Authors:
Ioannis Makos,
Jakub Benda,
David Busto,
Benjamin Steiner,
Barbara Merzuk,
Serguei Patchkovskii,
Van-Hung Hoang,
Uwe Thumm,
Zdeněk Mašín,
Giuseppe Sansone
Abstract:
Attosecond interferometry in a two-color field is central to attosecond metrology and spectroscopy. In this technique, a photoelectron wave packet is released when a single photon from an extreme ultraviolet comb is absorbed. The wave packet then either emits or absorbs one or more near-infrared photons, leading to the formation of sidebands of the main photoelectron peaks. This picture applies we…
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Attosecond interferometry in a two-color field is central to attosecond metrology and spectroscopy. In this technique, a photoelectron wave packet is released when a single photon from an extreme ultraviolet comb is absorbed. The wave packet then either emits or absorbs one or more near-infrared photons, leading to the formation of sidebands of the main photoelectron peaks. This picture applies well to atoms and assumes that the near-infrared laser pulse only acts on the photoelectron leaving the parent ion. The effect of the near-infrared pulse on the electronic structure of the cation is not considered, since the field usually cannot induce transitions between its electronic levels. Here, we demonstrate how dynamics induced by the near-infrared field in the cation can significantly impact the amplitude and phases of the sideband signal of the photoelectrons associated with specific dissociative channels of CO$_2$ molecules. This coupling of the near-infrared field with the molecular cation opens a third quantum pathway contributing to the signal measured in attosecond interferometry. Through angle- and energy-resolved characterization of the sideband oscillations, we observe reduction of interference amplitude over specific energy range upon angle integration. By comparison with theoretical predictions, we can isolate the contributions of specific interfering pathways to the two-color multi-pathway photoionization process. The scheme investigated in our work is general, and our observations highlight the importance of the additional pathway for accurately interpreting attosecond interferometry experiments involving molecules and more complex quantum systems.
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Submitted 25 April, 2026;
originally announced April 2026.
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Strong-Field Photoelectron Interferometry with Near-Single-Cycle Yb Lasers
Authors:
Mahmudul Hasan,
Phi-Hung Tran,
Jingsong Gao,
Van-Hung Hoang,
Ming-Shian Tsai,
Ming-Chang Chen,
Uwe Thumm,
Charles Lewis Cocke,
Chii-Dong Lin,
Anh-Thu Le,
and Meng Han
Abstract:
The concept of using photoelectron interferometry in short laser fields to probe electron dynamics and target structures was introduced more than two decades ago. However, the quality of experimental data has remained insufficient for quantitative analysis, largely due to the instability of few-cycle Ti:Sa laser pulses, the current workhorse of short pulses. Here, we report the first systematic st…
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The concept of using photoelectron interferometry in short laser fields to probe electron dynamics and target structures was introduced more than two decades ago. However, the quality of experimental data has remained insufficient for quantitative analysis, largely due to the instability of few-cycle Ti:Sa laser pulses, the current workhorse of short pulses. Here, we report the first systematic strong-field ionization experiments performed with industrial-grade, carrier-envelope-phase (CEP) stabilized, near-single-cycle Yb lasers. By measuring photoelectron momentum distributions in the direct-ionization regime, we show that single-cycle cosine-shaped pulses can separate and enhance both spider-leg and fishbone holographic structures. The spider-leg structure enables extraction of the electron scattering phase from the Ar atomic potential-information typically accessible only through attosecond metrology, while the fishbone structure reveals the orbital-parity contrast between Ar atoms and nitrogen molecules. Our measurements are quantitatively reproduced by both semiclassical Herman-Kluk-propagator and \textit{ab initio} simulations, paving the way for precision studies of electron-molecule scattering with widely accessible industrial-grade lasers.
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Submitted 2 September, 2025; v1 submitted 1 September, 2025;
originally announced September 2025.
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Photoelectron -- residual-ion entanglement in streaked shake-up ionization of helium
Authors:
Hongyu Shi,
Uwe Thumm
Abstract:
Streaked photoelectron emission spectra access the correlated dynamics of photoelectrons and residual target electrons with attosecond temporal resolution. We calculated ab initio single-ionization spectra for photoemission from helium atoms by co-linearly polarized ultrashort XUV and assisting few-femtosecond IR pulses. Distinguishing direct and shake-up ionization resulting in ground-state and e…
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Streaked photoelectron emission spectra access the correlated dynamics of photoelectrons and residual target electrons with attosecond temporal resolution. We calculated ab initio single-ionization spectra for photoemission from helium atoms by co-linearly polarized ultrashort XUV and assisting few-femtosecond IR pulses. Distinguishing direct and shake-up ionization resulting in ground-state and excited (n=2,3) He+ residual ions, respectively, we examined the effects of the correlated photoemission dynamics on the photoelectron phase-accumulation as a function of the observable photoelectron detection direction and kinetic energy, and XUV-IR pulse delay. We tracked the dynamical evolution of the residual ion in relative streaked photoemission delays and found dominant contributions for shake-up emission from the residual ion - photoelectron interaction. These are in very good and fair agreement, respectively, for n=2 and n=3 shake-up photoemission along the pulse-polarization directions, with previous experimental and theoretical investigations [Ossiander et. al. 2017] and reveal a strong photoemission-direction dependence for shake-up ionization due to the coupling between the photoelectron and evolving residual-ion charge distribution in the IR-laser field.
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Submitted 5 September, 2024;
originally announced September 2024.
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Simultaneous imaging of vibrational, rotational, and electronic wave packet dynamics in a triatomic molecule
Authors:
Huynh Van Sa Lam,
Van-Hung Hoang,
Anbu Selvam Venkatachalam,
Surjendu Bhattacharyya,
Keyu Chen,
Sina Jacob,
Sanduni Kudagama,
Tu Thanh Nguyen,
Daniel Rolles,
Uwe Thumm,
Artem Rudenko,
Vinod Kumarappan
Abstract:
Light-induced molecular dynamics often involve the excitation of several electronic, vibrational, and rotational states. Since the ensuing electronic and nuclear motion determines the pathways and outcomes of photoinduced reactions, our ability to monitor and understand these dynamics is crucial for molecular physics, physical chemistry, and photobiology. However, characterizing this complex motio…
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Light-induced molecular dynamics often involve the excitation of several electronic, vibrational, and rotational states. Since the ensuing electronic and nuclear motion determines the pathways and outcomes of photoinduced reactions, our ability to monitor and understand these dynamics is crucial for molecular physics, physical chemistry, and photobiology. However, characterizing this complex motion represents a significant challenge when different degrees of freedom are strongly coupled. In this Letter, we demonstrate how the interplay between vibrational, rotational, and electronic degrees of freedom governs the evolution of molecular wave packets in the low-lying states of strong-field-ionized sulfur dioxide. Using time-resolved Coulomb explosion imaging (CEI) and quantum mechanical wave packet simulations, we directly map the bending vibrations of the molecule, show how the vibrational wave packet is influenced by molecular alignment, and elucidate the consequences of nuclear motion for the coupling between the two lowest electronic states of the cation. Our results demonstrate that multi-coincident CEI can be an efficient experimental tool for characterizing coupled electronic and nuclear motion in polyatomic molecules.
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Submitted 6 June, 2025; v1 submitted 15 August, 2024;
originally announced August 2024.
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Strong-field control of plasmonic properties in core-shell nanoparticles
Authors:
Jeffrey Powell,
Jianxiong Li,
Adam Summers,
Seyyed Javad Robatjazi,
Michael Davino,
Philipp Rupp,
Erfan Saydanzad,
Christopher M. Sorensen,
Daniel Rolles,
Matthias F. Kling,
Carlos Trallero-Herrero,
Uwe Thumm,
Artem Rudenko
Abstract:
The strong-field control of plasmonic nanosystems opens up new perspectives for nonlinear plasmonic spectroscopy and petahertz electronics. Questions, however, remain regarding the nature of nonlinear light-matter interactions at sub-wavelength spatial and ultrafast temporal scales. Addressing this challenge, we investigated the strong-field control of the plasmonic response of Au nanoshells with…
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The strong-field control of plasmonic nanosystems opens up new perspectives for nonlinear plasmonic spectroscopy and petahertz electronics. Questions, however, remain regarding the nature of nonlinear light-matter interactions at sub-wavelength spatial and ultrafast temporal scales. Addressing this challenge, we investigated the strong-field control of the plasmonic response of Au nanoshells with a SiO$_2$ core to an intense laser pulse. We show that the photoelectron energy spectrum from these core-shell nanoparticles displays a striking transition between the weak and strong-field regime. This observed transition agrees with the prediction of our modified Mie-theory simulation that incorporates the nonlinear dielectric nanoshell response. The demonstrated intensity-dependent optical control of the plasmonic response in prototypical core-shell nanoparticles paves the way towards ultrafast switching and opto-electronic signal modulation with more complex nanostructures.
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Submitted 15 August, 2021;
originally announced August 2021.
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Enhanced high-harmonic generation from chromium-doped magnesium oxide
Authors:
V. E. Nefedova,
S. Fröhlich,
N. Tancogne-Dejean,
W. Boutu,
F. Navarrete,
M. F. Ciappina,
D. Franz,
D. Gauthier,
A. Hamdou,
S. Kaassamani,
R. Nicolas,
Q. Ripault,
G. Jargot,
U. Thumm,
M. Hanna,
P. Georges,
A. Rubio,
H. Merdji
Abstract:
High-order harmonic generation (HHG) from crystals offers a new source of coherent extreme ultraviolet (XUV) attosecond radiation.
High-order harmonic generation (HHG) from crystals offers a new source of coherent extreme ultraviolet (XUV) attosecond radiation.
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Submitted 30 September, 2020; v1 submitted 3 January, 2020;
originally announced January 2020.
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A semi-classical approach for solving the time-dependent Schrödinger equation in spatially inhomogeneous electromagnetic pulses
Authors:
Jianxiong Li,
Uwe Thumm
Abstract:
To solve the time-dependent Schrödinger equation in spatially inhomogeneous pulses of electromagnetic radiation, we propose an iterative semi-classical complex trajectory approach. In numerical applications, we validate this method against ab initio numerical solutions by scrutinizing (a) electronic states in combined Coulomb and spatially homogeneous laser fields and (b) streaked photoemission fr…
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To solve the time-dependent Schrödinger equation in spatially inhomogeneous pulses of electromagnetic radiation, we propose an iterative semi-classical complex trajectory approach. In numerical applications, we validate this method against ab initio numerical solutions by scrutinizing (a) electronic states in combined Coulomb and spatially homogeneous laser fields and (b) streaked photoemission from hydrogen atoms and plasmonic gold nanospheres. In comparison with streaked photoemission calculations performed in strong-field approximation, we demonstrate the improved reconstruction of the spatially inhomogeneous induced plasmonic infrared field near a nanoparticle surface from streaked photoemission spectra.
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Submitted 16 November, 2019;
originally announced December 2019.
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Streaking and Wigner time delays in photoemission from atoms and surfaces
Authors:
Chang-hua Zhang,
Uwe Thumm
Abstract:
Streaked photoemission metrology allows the observation of an apparent relative time delay between the detection of photoelectrons from different initial electronic states. This relative delay is obtained by recording the photoelectron yield as a function of the delay between an ionizing ultrashort extended ultraviolet (XUV) pulse and a streaking infrared (IR) pulse. Theoretically, photoemission d…
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Streaked photoemission metrology allows the observation of an apparent relative time delay between the detection of photoelectrons from different initial electronic states. This relative delay is obtained by recording the photoelectron yield as a function of the delay between an ionizing ultrashort extended ultraviolet (XUV) pulse and a streaking infrared (IR) pulse. Theoretically, photoemission delays can be defined based on i) the phase shift the photoelectron wavefunction accumulates during the release and propagation of the photoelectron (``Wigner delay") and, alternatively, ii) the streaking trace in the calculated photoemission spectrum (``streaking delay"). We investigate the relation between Wigner and streaking delays in the photoemission from atomic and solid-surface targets. For solid targets and assuming a vanishing IR-skin depth, both Wigner and streaking delays can be interpreted as an average propagation time needed by photoelectrons to reach the surface, while the two delays differ for non-vanishing skin depths. For atomic targets, the difference between Wigner and streaking delays depends on the range of the ionic potential.
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Submitted 7 June, 2011;
originally announced June 2011.
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Attosecond probing of instantaneous AC Stark shifts in helium atoms
Authors:
Feng He,
Camilo Ruiz,
Andreas Becker,
Uwe Thumm
Abstract:
Based on numerical solutions of the time-dependent Schrödinger equation for either one or two active electrons, we propose a method for observing instantaneous level shifts in an oscillating strong infrared (IR) field in time, using a single tunable attosecond pulse to probe excited states of the perturbed atom. The ionization probability in the combined fields depends on both, the frequency of th…
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Based on numerical solutions of the time-dependent Schrödinger equation for either one or two active electrons, we propose a method for observing instantaneous level shifts in an oscillating strong infrared (IR) field in time, using a single tunable attosecond pulse to probe excited states of the perturbed atom. The ionization probability in the combined fields depends on both, the frequency of the attosecond pulse and the time delay between both pulses, since the IR field shifts excited energy levels into and out of resonance with the attosecond probe pulse. We show that this method (i) allows the detection of instantaneous atomic energy gaps with sub-laser-cycle time resolution and (ii) can be applied as an ultrafast gate for more complex processes such as non-sequential double-ionization.
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Submitted 26 May, 2011;
originally announced May 2011.
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Dielectric response effects in attosecond time-resolved streaked photoelectron spectra of metal surfaces
Authors:
Chang-hua Zhang,
Uwe Thumm
Abstract:
The release of conduction-band electrons from a metal surface by a sub-femtosecond extreme ultraviolet (XUV) pulse, and their propagation through the solid, provokes a dielectric response in the solid that acts back on the photoelectron wave packet. We calculated the (wake) potential associated with this photoelectron self-interaction in terms of bulk and surface plasmon excitations and show that…
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The release of conduction-band electrons from a metal surface by a sub-femtosecond extreme ultraviolet (XUV) pulse, and their propagation through the solid, provokes a dielectric response in the solid that acts back on the photoelectron wave packet. We calculated the (wake) potential associated with this photoelectron self-interaction in terms of bulk and surface plasmon excitations and show that it induces a considerable, XUV-frequency-dependent temporal shift in laser-streaked XUV photoemission spectra, suggesting the observation of the ultrafast solid-state dielectric response in contemporary streaked photoemission experiments.
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Submitted 3 February, 2011;
originally announced February 2011.
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Electron-Ion Interaction Effects in Attosecond Time-Resolved Photoelectron Spectra
Authors:
C. -H. Zhang,
U. Thumm
Abstract:
Photoionization by attosecond (as) extreme ultraviolet (xuv) pulses into the laser-dressed continuum of the ionized atom is commonly described in strong-field approximation (SFA), neglecting the Coulomb interaction between the emitted photoelectron (PE) and residual ion. By solving the time-dependent Schödinger equation (TDSE), we identify a temporal shift $δτ$ in streaked PE spectra, which become…
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Photoionization by attosecond (as) extreme ultraviolet (xuv) pulses into the laser-dressed continuum of the ionized atom is commonly described in strong-field approximation (SFA), neglecting the Coulomb interaction between the emitted photoelectron (PE) and residual ion. By solving the time-dependent Schödinger equation (TDSE), we identify a temporal shift $δτ$ in streaked PE spectra, which becomes significant at small PE energies. Within an eikonal approximation, we trace this shift to the combined action of Coulomb and laser forces on the released PE, suggesting the experimental and theoretical scrutiny of their coupling in streaked PE spectra. The initial state polarization effect by the laser pulse on the xuv streaked spectrum is also examined.
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Submitted 20 September, 2010;
originally announced September 2010.
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Evidence for parallel confinement in resonant charge transfer of negative hydrogen ion near metal surfaces
Authors:
Himadri S. Chakraborty,
Thomas Niederhausen,
Uwe thumm
Abstract:
Using a wave packet propagation approach, we find that the resonant charge transfer process of H^- near a Cu(111) surface is strongly influenced by transient hybrid states. These states originate from an ion-induced confinement parallel to the surface together with the surface-localization character of the metal potential along the surface normal. The lowest members of these states have lifetime…
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Using a wave packet propagation approach, we find that the resonant charge transfer process of H^- near a Cu(111) surface is strongly influenced by transient hybrid states. These states originate from an ion-induced confinement parallel to the surface together with the surface-localization character of the metal potential along the surface normal. The lowest members of these states have lifetimes of the order of interaction times in typical particle-surface scattering experiments. The propagation of the electron probability density provides clear evidence for this effect in visualizing the evolution and the decay of these transient states.
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Submitted 8 May, 2003;
originally announced May 2003.
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Extended Classical Over-Barrier Model for Collisions of Highly Charged Ions with Conducting and Insulating Surfaces
Authors:
Jens J. Ducree,
Fulvio Casali,
Uwe Thumm
Abstract:
We have extended the classical over-barrier model to simulate the neutralization dynamics of highly charged ions interacting under grazing incidence with conducting and insulating surfaces. Our calculations are based on simple model rates for resonant and Auger transitions. We include effects caused by the dielectric response of the target and, for insulators, localized surface charges. Characte…
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We have extended the classical over-barrier model to simulate the neutralization dynamics of highly charged ions interacting under grazing incidence with conducting and insulating surfaces. Our calculations are based on simple model rates for resonant and Auger transitions. We include effects caused by the dielectric response of the target and, for insulators, localized surface charges. Characteristic deviations regarding the charge transfer processes from conducting and insulating targets to the ion are discussed. We find good agreement with previously published experimental data for the image energy gain of a variety of highly charged ions impinging on Au, Al, LiF and KI crystals.
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Submitted 28 November, 1997;
originally announced November 1997.