arXiv subjects

Hugo W. van der Hart

Publications and source records attributed to Hugo W. van der Hart.

7 recordsLinked to original sources

arXiv2026

Roadmap on Attosecond Science

Twenty-five years have passed since the first experimental demonstration of attosecond pulses, marking the advent of our ability to resolve and control electron motion in real time. What began as a technological breakthrough - generating the shortest flashes ever produced - has evolved into a powerful approach for probing and steering electronic dynamics in atoms, molecules, and solids. This roadmap, authored by leading experts in the field, surveys the recent rapid progress in the generation and characterization of attosecond pulses, emerging attosecond measurement and control techniques, and their expanding range of applications. It reviews current and future developments in attosecond light sources, including novel laser technologies, waveform synthesizers, new schemes for high-order harmonic generation, attosecond pulse generation at free-electron lasers, and structured light. Advances in attosecond measurement methodologies are also discussed, encompassing all-attosecond pump-probe spectroscopy, attosecond four-wave mixing, attosecond microscopy, spectroscopy with light transients, and attosecond interferometry. Furthermore, the roadmap addresses applications of attosecond spectroscopy to reveal electron dynamics in molecules and condensed matter systems from both theoretical and experimental perspectives, and highlights emerging directions at the interface with quantum optics and quantum entanglement. Overall, this work aims to serve as a comprehensive resource for navigating the evolving landscape of attosecond science.

physics.optics↗

arXiv2021

Enhancing spin polarization using ultrafast angular streaking

Through solution of the multielectron, semi-relativistic, time-dependent Schrödinger equation, we show that angular streaking produces strongly spin-polarized electrons in a noble gas. The degree of spin polarization increases with the Keldysh parameter, so that angular streaking -- ordinarily applied to investigate tunneling -- may be repurposed to generate strongly spin-polarized electron bunches. Additionally, we explore modifications of the angular streaking scheme that also enhance spin polarization.

physics.atom-ph↗

arXiv2020

Polarization control of high-harmonic generation via the spin-orbit interaction

We observe the generation of high harmonics in the plane perpendicular to the driving laser polarization and show that these are driven by the spin-orbit interaction. Using R-Matrix with time-dependence theory, we demonstrate that for certain initial states either circularly- or linearly- polarized harmonics arise via well-known selection rules between atomic states controlled by the spin-orbit interaction. Finally, we elucidate the connection between the observed harmonics and the phase of the intial state.

physics.atom-ph↗

arXiv2019

Resolving Ultra-Fast Spin-Orbit Dynamics in Heavy Many-Electron Atoms

We use R-Matrix with Time-dependence (RMT) theory, with spin-orbit effects included, to study krypton irradiated by two time-delayed XUV ultrashort pulses. The first pulse excites the atom to 4s$^{2}$4p$^{5}$5s. The second pulse then excites 4s4p$^{6}$5s autoionising levels, whose population can be observed through their subsequent decay. By varying the time delay between the two pulses, we are able to control the excitation pathway to the autoionising states. The use of cross-polarised light pulses allows us to isolate the two-photon pathway, with one photon taken from each pulse.

physics.atom-ph↗

arXiv2016

Spin and spatial dynamics in electron-impact scattering off S-wave He using R-matrix with Time-Dependence theory

R-matrix with time-dependence theory is applied to electron-impact ionisation processes for He in the S-wave model. Cross sections for electron-impact excitation, ionisation and ionisation with excitation for impact energies between 25 and 225 eV are in excellent agreement with benchmark cross sections. Ultra-fast dynamics induced by a scattering event is observed through time-dependent signatures associated with autoionisation from doubly excited states. Further insight into dynamics can be obtained through examination of the spin components of the time-dependent wavefunction.

physics.atom-ph↗

arXiv2013

Anisotropy parameters in two-colour two-photon above threshold ionization

We employ the time-dependent R-Matrix (TDRM) method to calculate anisotropy parameters for positive and negative sidebands of selected harmonics generated by two-color two-photon above threshold ionization of argon. We consider odd harmonics of an 800 nm field ranging from the 13th to 19th harmonic, overlapped by a fundamental 800 nm IR field. The anisotropy parameters obtained using the TDRM method are compared with those obtained using a second order perturbation theory with a model potential (MP) approach and a soft photon approximation (SPA) approach. Where available, a comparison is also made to published experimental results. All three theoretical approaches provide similar values for anisotropy parameters. The TDRM approach obtains values that are closest to published experimental values. At high photon energies, the differences between each of the theoretical methods become less significant.

physics.atom-ph↗

arXiv2013

Enhanced Harmonic Generation from M=1 aligned Ar+

We investigate harmonic generation (HG) from ground-state Ar+ aligned with M=1 at a laser wavelength of 390-nm and intensity of 4x10(14) Wcm-2. Using time-dependent R-matrix theory, we find that an initial state with magnetic quantum number M=1 provides a 4-fold increase in harmonic yield over M=0. HG arises primarily from channels associated with the (3)Pe threshold of Ar2+, in contrast with M=0 for which channels associated with the excited, (1)De threshold dominate HG. Multichannel and multielectron interferences lead to a more marked suppression of HG for M=1 than M=0.

physics.atom-ph↗