Criteria for the observation of strong-field photoelectron holography

Photoelectron holography is studied experimentally and computationally using the ionization of ground-state xenon atoms by intense near-infrared radiation. A strong dependence of the occurrence of the holographic pattern on the laser wavelength and intensity is observed, and it is shown that the observation of the hologram requires that the ponderomotive energy Up is substantially larger than the photon energy. The holographic interference is therefore favored by longer wavelengths and higher laser intensities. Our results indicate that the tunneling regime is not a necessary condition for the observation of the holographic pattern, which can be observed under the conditions formally attributed to the multiphoton regime. © 2011 American Physical Society

Attosecond time-resolved photoelectron holography

Ultrafast strong-field physics provides insight into quantum phenomena that evolve on an attosecond time scale, the most fundamental of which is quantum tunneling. The tunneling process initiates a range of strong field phenomena such as high harmonic generation (HHG), laser-induced electron diffraction, double ionization and photoelectron holography—all evolving during a fraction of the optical cycle. Here we apply attosecond photoelectron holography as a method to resolve the temporal properties of the tunneling process. Adding a weak second harmonic (SH) field to a strong fundamental laser field enables us to reconstruct the ionization times of photoelectrons that play a role in the formation of a photoelectron hologram with attosecond precision. We decouple the contributions of the two arms of the hologram and resolve the subtle differences in their ionization times, separated by only a few tens of attoseconds

Population transfer to high angular momentum states in infrared-assisted XUV photoionization of helium

An extreme-ultraviolet (XUV) laser pulse consisting of harmonics of a fundamental near-infrared (NIR) laser frequency is combined with the NIR pulse to systematically study two-color photoionization of helium atoms. A time-resolved photoelectron spectroscopy experiment is carried out where energy- A nd angle-resolved photoelectron distributions are obtained as a function of the NIR intensity and wavelength. Time-dependent Schrödinger equation calculations are performed for the conditions corresponding to the experiment and used to extract residual populations of Rydberg states resulting from excitation by the XUV + NIR pulse pair. The residual populations are studied as a function of the NIR intensity (3.5 × 1010-8 × 1012 W cm-2) and wavelength (760-820 nm). The evolution of the photoelectron distribution and the residual populations are interpreted using an effective restricted basis model, which includes the minimum set of states relevant to the features observed in the experiments. As a result, a comprehensive and intuitive picture of the laser-induced dynamics in helium atoms exposed to a two-color XUV-NIR light field is obtained. © 2020 The Author(s). Published by IOP Publishing Ltd

Control of the Coulomb explosion of I

We present calculated results for the optimization highly-charged fragment ion formation in the Coulomb explosion of I2 in an intense laser field. Calculations are performed using a simple genetic algorithm and a classical model for the Coulomb explosion process. We find that at low intensity the production of highly-charged fragment ions is optimized by a Fourier-limited pulse, whereas at higher intensity the Coulomb explosion is optimized by a sequence of pulses, with a time-separation determined by enhanced ionization at the critical internuclear distance. Our calculations provide insight into the sensitivity of adaptive pulse shaping experiments to the parameters and evolutionary approaches used

Time-dependent fragment distributions detected via pump-probe ionisation: a theoretical approach

We show how in molecular predissociation a method combining ultrafast pump-probe techniques with a measurement of the relative recoil velocity can map time-dependent neutral fragment distributions into the ionic continuum. With an appropriate probe pulse exciting a resonant transition (such as (1+1) Resonance Enhanced Multiphoton Ionisation, or excitation of ZEKE states), the temporal evolution of fragment distributions can in principle be measured. Numerical simulations on NaI predissociation are compared to a simple approximate mapping interpretation. The results are discussed in terms of the interplay between temporal and energetic resolution with respect to current experimental limitations

Femtosecond XUV induced dynamics of the methyl iodide cation

XXI International Conference on Ultrafast Phenomena 2018 (UP 2018). -- 3 pags, 1 figXUV wavelength-selected pulses obtained with high harmonic generation are studies of cation dynamics with state-by-state resolution. We demonstrate this by pump-probe experiments on CH3I+ cations and identify both resonant and non-resonant dynamics

Femtosecond XUV-IR induced photodynamics in the methyl iodide cation

12 pags., 7 figs., 1 tab.The time-resolved photodynamics of the methyl iodide cation (CH3I+) are investigated by means of femtosecond XUV-IR pump-probe spectroscopy. A time-delay-compensated XUV monochromator is employed to isolate a specific harmonic, the 9th harmonic of the fundamental 800 nm (13.95 eV, 88.89 nm), which is used as a pump pulse to prepare the cation in several electronic states. A time-delayed IR probe pulse is used to probe the dissociative dynamics on the first excited state potential energy surface. Photoelectrons and photofragment ions - and I+ - are detected by velocity map imaging. The experimental results are complemented with high level ab initio calculations for the potential energy curves of the electronic states of CH3I+ as well as with full dimension on-the-fly trajectory calculations on the first electronically excited state, considering the presence of the IR pulse. The and I+ pump-probe transients reflect the role of the IR pulse in controlling the photodynamics of CH3I+ in the state, mainly through the coupling to the ground state and to the excited state manifold. Oscillatory features are observed and attributed to a vibrational wave packet prepared in the state. The IR probe pulse induces a coupling between electronic states leading to a slow depletion of fragments after the cation is transferred to the ground states and an enhancement of I+ fragments by absorption of IR photons yielding dissociative photoionization.MLMS acknowledges financial support through a predoctoral contract from Universidad Complutense de Madrid (Spain) and FULMATEN-CM project funded by Madrid Regional Government under programme Y2018/NMT-5028. GR thanks the Netherlands Organization for Scientific Research (NWO) for financial support (Rubicon 68-50-1410). This project has received funding (SMP) from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant agreement No. 842539 (ATTO-CONTROL) and has been financed in part by the Spanish State Research Agency (AEI/10.13039/501100011033), Grants PGC2018-096444-B-I00, PID2019-106125GB-I00 and PID2019-106732GB-I00, and the Madrid Regional Government through the program Proyectos Sin´ergicos de I + D (Grant Y2018/NMT-5028 FULMATEN-CM). FM acknowledges support from the ‘Severo Ochoa’ Programme for Centres of Excellence in R & D (SEV-2016-0686) and the ‘María de Maeztu’ Programme for Units of Excellence in R & D (CEX2018-000805-M). All calculations were performed at the Mare Nostrum Supercomputer of the Red Española de Supercomputacion (BSC-RES) and the Centro de Computaci ´ on´ Científica de la Universidad Autonoma de Madrid (CCC-UAM). MV and OK acknowledge the support ´ from the Deutsche Forschungsgeminschaft (KO 4920/1-1). This work was performed in the Max Born Institut (Berlin) in the kHz Laboratory and received financial support from LaserLab Europe through the MBI002239 project