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- ItemDelayed relaxation of highly excited naphthalene cations(Bristol : IOP Publ., 2020) Reitsma, G.; Hummert, J.; Dura, J.; Loriot, V.; Vrakking, M.J.J.; Lépine, F.; Kornilov, O.The efficiency of energy transfer in ultrafast electronic relaxation of molecules depends strongly on the complex interplay between electronic and nuclear motion. In this study we use wavelength-selected XUV pulses to induce relaxation dynamics of highly excited cationic states of naphthalene. Surprisingly, the observed relaxation lifetimes increase with the cationic excitation energy. We propose that this is a manifestation of a quantum mechanical population trapping that leads to delayed relaxation of molecules in the regions with a high density of excited states. © 2019 Published under licence by IOP Publishing Ltd.
- ItemRobust transverse structures in rescattered photoelectron wavepackets and their consequences(Bristol : IOP Publ., 2020) Bredtmann, T.; Patchkovskii, S.Initial-state symmetry has been under-appreciated in strong-field spectroscopies, where laser fields dominate the dynamics. We demonstrate numerically that the transverse photoelectron phase structure, arising from the initial-state symmetry, is robust in strong-field rescattering, and has pronounced effects on strong-field photoelectron spectra. Interpretation of rescattering experiments need to take these symmetry effects into account. In turn, robust transverse photoelectron phase structures may enable attosecond sub-Ångström super-resolution imaging with structured electron beams.
- ItemStrong-Field Ionization of Linear Molecules by a Bichromatic Elliptically Polarized Laser Field with Coplanar Counterrotating or Corotating Components of Different Frequencies(Bristol : IOP Publ., 2020) Gazibegović-Busuladžić, A.; Busuladžić, M.; Čerkić, A.; Hasović, E.; Becker, W.; Milošević, D.B.We investigate strong-field ionization of linear molecules by a two-color laser field of frequencies rω and sω having coplanar counterrotating or corotating elliptically polarized components (ω is the fundamental laser field frequency and r and s are integers). Using the improved molecular strong-field approximation we analyze direct above-threshold ionization (ATI) and high-order ATI (HATI) spectra. More precisely, reflection and rotational symmetries of these spectra for linear molecules aligned in the laser-field polarization plane are considered. The reflection symmetries for particular molecular orientations, known to be valid for a bicircular field (this is the field with circularly polarized counterrotating components), are valid also for arbitrary component ellipticities. However, specific rotational symmetries that are satisfied for HATI by a bicircular field, are violated for an arbitrary elliptically polarized field with counterrotating components. For the corotating case and the N2 molecule we analyze molecular-orientation-dependent interferences and plateau structures for various ellipticities.
- ItemGeneration of elliptically polarized soft x rays using high-order harmonic generation with orthogonal two-color laser fields(Bristol : IOP Publ., 2020) Milošević, D.B.; Becker, W.High-order harmonic generation by orthogonally polarized two-color (OTC) laser fields is analysed using strong-field approximation and quantum-orbit theory. Results for the field components frequency ratio of 2:1 and 3:1 are presented and compared. We have shown that, depending on the relative phase between the field components, the shape of the high-harmonic spectrum can be very different from that obtained by a monochromatic linearly polarized laser field. It is also shown that it is possible to generate elliptically polarized high-order harmonics with very high photon energies using OTC laser field with the frequency ratio of 3:1 and a long fundamental wavelength. An effective relative phase control of the harmonic emission is demonstrated. The obtained results are explained using the quantum-orbit theory. © Published under licence by IOP Publishing Ltd.
- ItemGeneration and characterization of isolated attosecond pulses for coincidence spectroscopy at 100 kHz repetition rate(Bristol : IOP Publ., 2020) Witting, T.; Furch, F.; Osolodkov, M.; Schell, F.; Menoni, C.; Schulz, C.P.; Vrakking, M.J.J.An attosecond pump-probe beamline with 100 kHz repetition rate for coincidence experiments has been developed. It is based on non-collinear optical parametric chirped pulse ampli-cation and delivers 100 µJ sub-4 fs to an high-harmonic generation source. Details on the generation and characterization of isolated attosecond pulses will be presented. © 2019 Published under licence by IOP Publishing Ltd.
- ItemAtomic and molecular suite of R-matrix codes for ultrafast dynamics in strong laser fields and electron/positron scattering(Bristol : IOP Publ., 2020) Wragg, J.; Benda, J.; Mašín, Z.; Armstrong, G.S.J.; Clarke, D.D.A.; Brown, A.C.; Ballance, C.; Harvey, A.G.; Houfek, K.; Sunderland, A.; Plummer, M.; Gorfinkiel, J.D.; Van Der Hart, H.We describe and illustrate a number of recent developments of the atomic and molecular ab initio R-matrix suites for both time-dependent calculations of ultrafast laser-induced dynamics and time-independentcalculations of photoionization and electron scattering. © 2019 Published under licence by IOP Publishing Ltd.
- ItemSignatures of Light-Induced Potential Energy Surfaces in H2+(Bristol : IOP Publ., 2020) Kübel, M.; Spanner, M.; Dube, Z.; Naumov, A. Yu; Vrakking, M.J.J.; Corkum, P.B.; Villeneuve, D.M.; Staudte, A.Using theory and Cold Target Recoil Ion Momentum Spectroscopy we find signatures of light-induced molecular potential energy surfaces in the 3-dimensional proton momentum distributions of dissociating H+2. © 2020 Journal of Physics: Conference Series. All rights reserved.
- ItemMolecular Auger Interferometry(Bristol : IOP Publ., 2020) Khokhlova, M.; Cooper, B.; Ueda, K.; Prince, K.C.; Kolorenč, P.; Ivanov, M.; Averbukh, V.We propose a theory of interferometric measurement of a normal Auger decay width in molecules. Molecular Auger interferometry is based on the coherent phase control of Auger dynamics in a two-colour (ω/2ω) laser field. We show that, in contrast to atoms, in oriented molecules of certain point groups (e.g. CH3F) the relative ω/2ω phase modulates the total ionisation yield. A simple analytical formula is derived for the extraction of the widths of Auger-active states from a molecular Auger interferogram, avoiding the need of either attosecond or high-resolution spectroscopy.
- ItemUltrafast Structural Changes in Chiral Molecules Measured with Free-Electron Lasers(Bristol : IOP Publ., 2020) Schmidt, P.; Music, V.; Hartmann, G.; Boll, R.; Erk, B.; Bari, S.; Allum, F.; Baumann, T.M.; Brenner, G.; Brouard, M.; Burt, M.; Coffee, R.; Dörner, S.; Galler, A.; Grychtol, P.; Heathcote, D.; Inhester, L.; Kazemi, M.; Larsson, M.; Li, Z.; Lutmann, A.; Manschwetus, B.; Marder, L.; Mason, R.; Moeller, S.; Osipov, T.; Otto, H.; Passow, C.; Rolles, D.; Rupprecht, P.; Schubert, K.; Schwob, L.; Thomas, R.; Vallance, C.; Von Korff Schmising, C.; Wagner, R.; Walter, P.; Wolf, T.J.A.; Zhaunerchyk, V.; Meyer, M.; Ehresmann, A.; Knie, A.; Demekhin, P.V.; Ilchen, M.(X-ray) free-electron lasers are employed to site specifically interrogate atomic fragments during ultra-fast photolysis of chiral molecules via time-resolved photoelectron circular dichroism. © 2020 Institute of Physics Publishing. All rights reserved.
- ItemPopulation transfer to high angular momentum states in infrared-assisted XUV photoionization of helium(Bristol : IOP Publ., 2020) Mayer, Nicola; Peng, Peng; Villeneuve, David M.; Patchkovskii, Serguei; Ivanov, Misha; Kornilov, Oleg; Vrakking, Marc J.J.; Niikura, HiromichiAn 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.