| 1. |
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| 2. |
- Allum, Felix, et al.
(författare)
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Coulomb explosion imaging of CH3I and CH2CII photodissociation dynamics
- 2018
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 149:20
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Tidskriftsartikel (refereegranskat)abstract
- The photodissociation dynamics of CH3I and CH2CII at 272 nm were investigated by time-resolved Coulomb explosion imaging, with an intense non-resonant 815nmprobe pulse. Fragment ion momenta over a widem/z range were recorded simultaneously by coupling a velocity map imaging spectrometer with a pixel imaging mass spectrometry camera. For both molecules, delay-dependent pump-probe features were assigned to ultraviolet-induced carbon-iodine bond cleavage followed by Coulomb explosion. Multi-mass imaging also allowed the sequential cleavage of both carbon-halogen bonds in CH2ClI to be investigated. Furthermore, delay-dependent relative fragment momenta of a pair of ions were directly determined using recoil-frame covariance analysis. These results are complementary to conventional velocity map imaging experiments and demonstrate the application of time-resolved Coulomb explosion imaging to photoinduced real-time molecular motion.
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| 3. |
- Arnold, Cord L., et al.
(författare)
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Spatiotemporal coupling of attosecond pulses
- 2019
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Ingår i: 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019. - 9781728104690 ; Part F140-CLEO_Europe 2019
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Konferensbidrag (refereegranskat)abstract
- Attosecond pulses in the extreme ultraviolet (XUV) spectral range are today routinely generated via high-order harmonic generation (HHG), when intense ultrashort laser pulses are focused into a gaseous generation medium. The effect is most easily understood in a semi-classical picture [1]. An electron can tunnel ionize from the distorted atomic potential, pick up kinetic energy in the laser field, potentially return to its parent ion and recombine. The excess energy is emitted as XUV photon. The process repeats for every half-cycle of the driving field, resulting in a train of attosecond pulses and in the frequency domain in the well-known, odd-order comb of harmonics. Two main families of electron trajectories leading to the same photon energy can be distinguished into 'short' and 'long', according to their time of travel in the continuum. Due to the complicated nature of the HHG process, attosecond pulses usually cannot be separated into their temporal and spatial profiles, but instead have strong chromatic aberration and are spatio-temporally coupled [2-4].
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| 4. |
- Brasse, Felix, et al.
(författare)
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Time-resolved inner-shell photoelectron spectroscopy : From a bound molecule to an isolated atom
- 2018
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 97:4
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Tidskriftsartikel (refereegranskat)abstract
- Due to its element and site specificity, inner-shell photoelectron spectroscopy is a widely used technique to probe the chemical structure of matter. Here, we show that time-resolved inner-shell photoelectron spectroscopy can be employed to observe ultrafast chemical reactions and the electronic response to the nuclear motion with high sensitivity. The ultraviolet dissociation of iodomethane (CH3I) is investigated by ionization above the iodine 4d edge, using time-resolved inner-shell photoelectron and photoion spectroscopy. The dynamics observed in the photoelectron spectra appear earlier and are faster than those seen in the iodine fragments. The experimental results are interpreted using crystal-field and spin-orbit configuration interaction calculations, and demonstrate that time-resolved inner-shell photoelectron spectroscopy is a powerful tool to directly track ultrafast structural and electronic transformations in gas-phase molecules.
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| 5. |
- Burt, Michael, et al.
(författare)
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Coulomb-explosion imaging of concurrent CH2BrI photodissociation dynamics
- 2017
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 96:4
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics following laser-induced molecular photodissociation of gas-phase CH2BrI at 271.6 nm were investigated by time-resolved Coulomb-explosion imaging using intense near-IR femtosecond laser pulses. The observed delay-dependent photofragment momenta reveal that CH2BrI undergoes C-I cleavage, depositing 65.6% of the available energy into internal product states, and that absorption of a second UV photon breaks the C-Br bond of C(H)2Br. Simulations confirm that this mechanism is consistent with previous data recorded at 248 nm, demonstrating the sensitivity of Coulomb-explosion imaging as a real-time probe of chemical dynamics.
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| 6. |
- Busto, David, et al.
(författare)
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Fano's Propensity Rule in Angle-Resolved Attosecond Pump-Probe Photoionization
- 2019
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 123:13
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Tidskriftsartikel (refereegranskat)abstract
- In a seminal article, Fano predicts that absorption of light occurs preferably with increase of angular momentum. We generalize Fano's propensity rule to laser-assisted photoionization, consisting of absorption of an extreme-ultraviolet photon followed by absorption or emission of an infrared photon. The predicted asymmetry between absorption and emission leads to incomplete quantum interference in attosecond photoelectron interferometry. It explains both the angular dependence of the photoionization time delays and the delay dependence of the photoelectron angular distributions. Our theory is verified by experimental results in Ar in the 20-40 eV range.
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| 7. |
- Cheng, Yu Chen, et al.
(författare)
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Imaging multiphoton ionization dynamics of CH3I at a high repetition rate XUV free-electron laser
- 2021
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Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 54:1
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Tidskriftsartikel (refereegranskat)abstract
- XUV multiphoton ionization of molecules is commonly used in free-electron laser experiments to study charge transfer dynamics. However, molecular dissociation and electron dynamics, such as multiple photon absorption, Auger decay, and charge transfer, often happen on competing time scales, and the contributions of individual processes can be difficult to unravel. We experimentally investigate the Coulomb explosion dynamics of methyl iodide upon core-hole ionization of the shallow inner-shell of iodine (4d) and classically simulate the fragmentation by phenomenologically introducing ionization dynamics and charge transfer. Under our experimental conditions with medium fluence and relatively long XUV pulses (similar to 75 fs), we find that fast Auger decay prior to charge transfer significantly contributes to the charging mechanism, leading to a yield enhancement of higher carbon charge states upon molecular dissociation. Furthermore, we argue for the existence of another charging mechanism for the weak fragmentation channels leading to triply charged carbon atoms. This study shows that classical simulations can be a useful tool to guide the quantum mechanical description of the femtosecond dynamics upon multiphoton absorption in molecular systems.
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| 8. |
- Coudert-Alteirac, Hélène, et al.
(författare)
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Micro-focusing of broadband high-order harmonic radiation by a double toroidal mirror
- 2017
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Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 7:11
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Tidskriftsartikel (refereegranskat)abstract
- We present an optical system based on two toroidal mirrors in aWolter configuration to focus broadband extreme ultraviolet (XUV) radiation. Optimization of the focusing optics alignment is carried out with the aid of an XUV wavefront sensor. Back-propagation of the optimized wavefront to the focus yields a focal spot of 3.6 × 4.0 μm2 full width at half maximum, which is consistent with ray-tracing simulations that predict a minimum size of 3.0 × 3.2 μm2. This work is important for optimizing the intensity of focused high-order harmonics in order to reach the nonlinear interaction regime.
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| 9. |
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| 10. |
- Dacasa, Hugo, et al.
(författare)
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Single-shot extreme-ultraviolet wavefront measurements of high-order harmonics
- 2019
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Ingår i: Optics Express. - 1094-4087. ; 27:3, s. 2656-2670
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Tidskriftsartikel (refereegranskat)abstract
- We perform wavefront measurements of high-order harmonics using an extreme-ultraviolet (XUV) Hartmann sensor and study how their spatial properties vary with different generation parameters, such as pressure in the nonlinear medium, fundamental pulse energy and duration as well as beam size. In some conditions, excellent wavefront quality (up to 휆/11) was obtained. The high throughput of the intense XUV beamline at the Lund Laser Centre allows us to perform single-shot measurements of both the full harmonic beam generated in argon and individual harmonics selected by multilayer mirrors. We theoretically analyze the relationship between the spatial properties of the fundamental and those of the generated high-order harmonics, thus gaining insight into the fundamental mechanisms involved in high-order harmonic generation (HHG).
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| 11. |
- Ganguly, Smita, et al.
(författare)
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Coincidence study of core-ionized adamantane: Site-sensitivity within a carbon cage?
- 2022
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Ingår i: Physical chemistry chemical physics : PCCP. - 1463-9084. ; 24:47, s. 28994-29003
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the fragmentation dynamics of adamantane dications produced after core-ionization at the carbon edge followed by Auger decay. The combination of high-resolution electron spectroscopy, energy-resolved electron-ion multi-coincidence spectroscopy and different theoretical models allows us to give a complete characterization of the processes involved after ionization. We show that energy- and site-sensitivity is observed even for a highly-symmetric molecule that lacks any unique atomic site.
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| 12. |
- Ganguly, Smita, et al.
(författare)
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Resonant Inner-Shell Photofragmentation of Adamantane (C10H16)
- 2023
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Ingår i: Molecules. - 1420-3049. ; 28:14
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Tidskriftsartikel (refereegranskat)abstract
- Adamantane, the smallest diamondoid molecule with a symmetrical cage, contains two distinct carbon sites, CH and CH2. The ionization/excitation of the molecule leads to the cage opening and strong structural reorganization. While theoretical predictions suggest that the carbon site CH primarily causes the cage opening, the role of the other CH2 site remains unclear. In this study, we used advanced experimental Auger electron-ion coincidence techniques and theoretical calculations to investigate the fragmentation dynamics of adamantane after resonant inner-shell photoexcitation. Our results demonstrate that some fragmentation channels exhibit site-sensitivity of the initial core-hole location, indicating that different carbon site excitations could lead to unique cage opening mechanisms.
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| 13. |
- Garg, D., et al.
(författare)
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Fragmentation Dynamics of Fluorene Explored Using Ultrafast XUV-Vis Pump-Probe Spectroscopy
- 2022
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Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- We report on the use of extreme ultraviolet (XUV, 30.3 nm) radiation from the Free-electron LASer in Hamburg (FLASH) and visible (Vis, 405 nm) photons from an optical laser to investigate the relaxation and fragmentation dynamics of fluorene ions. The ultrashort laser pulses allow to resolve the molecular processes occurring on the femtosecond timescales. Fluorene is a prototypical small polycyclic aromatic hydrocarbon (PAH). Through their infrared emission signature, PAHs have been shown to be ubiquitous in the universe, and they are assumed to play an important role in the chemistry of the interstellar medium. Our experiments track the ionization and dissociative ionization products of fluorene through time-of-flight mass spectrometry and velocity-map imaging. Multiple processes involved in the formation of each of the fragment ions are disentangled through analysis of the ion images. The relaxation lifetimes of the excited fluorene monocation and dication obtained through the fragment formation channels are reported to be in the range of a few tens of femtoseconds to a few picoseconds.
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| 14. |
- Hoflund, Maria, et al.
(författare)
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Focusing Properties of High-Order Harmonics
- 2021
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Ingår i: Ultrafast Science. - : American Association for the Advancement of Science (AAAS). - 2765-8791. ; 2021
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Tidskriftsartikel (refereegranskat)abstract
- Many applications of the extreme ultraviolet (XUV) radiation obtained by high-order harmonic generation (HHG) in gases require a small focus area in order to enable attosecond pulses to reach a high intensity. Here, high-order harmonics generated in Ar with a multiterawatt laser system in a loose focusing geometry are focused to a few micrometers using two toroidal mirrors in a Wolter configuration with a high demagnification factor. Using a knife-edge measurement technique, we determine the position and size of the XUV foci as a function of harmonic order. We show that the focus properties vary with harmonic order and the generation conditions. Simulations, based on a classical description of the harmonic dipole phase and assuming that the individual harmonics can be described as Gaussian beams, reproduce the experimental behavior. We discuss how the generation geometry affects the intensity and duration of the focused attosecond pulses
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| 15. |
- Kockert, Hansjochen, et al.
(författare)
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UV-induced dissociation of CH2BrI probed by intense femtosecond XUV pulses
- 2022
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Ingår i: JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 55:1
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Tidskriftsartikel (refereegranskat)abstract
- The ultraviolet (UV)-induced dissociation and photofragmentation of gas-phase CH2BrI molecules induced by intense femtosecond extreme ultraviolet (XUV) pulses at three different photon energies are studied by multi-mass ion imaging. Using a UV-pump-XUV-probe scheme, charge transfer between highly charged iodine ions and neutral CH2Br radicals produced by C-I bond cleavage is investigated. In earlier charge-transfer studies, the center of mass of the molecules was located along the axis of the bond cleaved by the pump pulse. In the present case of CH2BrI, this is not the case, thus inducing a rotation of the fragment. We discuss the influence of the rotation on the charge transfer process using a classical over-the-barrier model. Our modeling suggests that, despite the fact that the dissociation is slower due to the rotational excitation, the critical interatomic distance for charge transfer is reached faster. Furthermore, we suggest that charge transfer during molecular fragmentation may be modulated in a complex way.
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| 16. |
- Kühn, Sergei, et al.
(författare)
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The ELI-ALPS facility : The next generation of attosecond sources
- 2017
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 50:13
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Forskningsöversikt (refereegranskat)abstract
- This review presents the technological infrastructure that will be available at the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI-ALPS) international facility. ELI-ALPS will offer to the international scientific community ultrashort pulses in the femtosecond and attosecond domain for time-resolved investigations with unprecedented levels of high quality characteristics. The laser sources and the attosecond beamlines available at the facility will make attosecond technology accessible for scientists lacking access to these novel tools. Time-resolved investigation of systems of increasing complexity is envisaged using the end stations that will be provided at the facility.
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| 17. |
- Kukk, E., et al.
(författare)
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Energy-dependent timescales in the dissociation of diiodothiophene dication
- 2023
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 25:7, s. 5795-5807
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Tidskriftsartikel (refereegranskat)abstract
- Photodissociation molecular dynamics of gas-phase 2,5-diiodothiophene molecules was studied in an electron-energy-resolved electron-multi-ion coincidence experiment performed at the FinEstBeAMS beamline of MAX IV synchrotron. Following the photoionization of the iodine 4d subshell and the Auger decay, the dissociation landscape of the molecular dication was investigated as a function of the Auger electron energy. Concentrating on an major dissociation pathway, C4H2I2S2+ -> C4H2S+ + I+ + I, and accessing the timescales of the process via ion momentum correlation analysis, it was revealed how this three-body process changes depending on the available internal energy. Using a generalized secondary dissociation model, the process was shown to evolve from secondary dissociation regime towards concerted dissociation as the available energy increased, with the secondary dissociation time constant changing from 1.5 ps to 129 fs. The experimental results were compared with simulations using a stochastic charge-hopping molecular mechanics model. It represented the observed trend and also gave a fair quantitative agreement with the experiment.
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| 18. |
- Lee, Jason W.l., et al.
(författare)
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The Kinetic Energy of PAH Dication and Trication Dissociation Determined by Recoil-Frame Covariance Map Imaging
- 2022
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Ingår i: Physical Chemistry Chemical Physics. - 1463-9084. ; 24:38, s. 23096-23105
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the dissociation of dications and trications of three polycyclic aromatic hydrocarbons (PAHs), fluorene, phenanthrene, and pyrene. PAHs are a family of molecules ubiquitous in space and involved in much of the chemistry of the interstellar medium. In our experiments, ions are formed by interaction with 30.3 nm extreme ultraviolet (XUV) photons, and their velocity map images are recorded using a PImMS2 multi-mass imaging sensor. Application of recoil-frame covariance analysis allows the total kinetic energy release (TKER) associated with multiple fragmentation channels to be determined to high precision, ranging 1.94-2.60 eV and 2.95-5.29 eV for the dications and trications, respectively. Experimental measurements are supported by Born-Oppenheimer molecular dynamics (BOMD) simulations.
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| 19. |
- Lee, J. W. L., et al.
(författare)
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The kinetic energy of PAH dication and trication dissociation determined by recoil-frame covariance map imaging
- 2022
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:38, s. 23096-23105
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the dissociation of dications and trications of three polycyclic aromatic hydrocarbons (PAHs), fluorene, phenanthrene, and pyrene. PAHs are a family of molecules ubiquitous in space and involved in much of the chemistry of the interstellar medium. In our experiments, ions are formed by interaction with 30.3 nm extreme ultraviolet (XUV) photons, and their velocity map images are recorded using a PImMS2 multi-mass imaging sensor. Application of recoil-frame covariance analysis allows the total kinetic energy release (TKER) associated with multiple fragmentation channels to be determined to high precision, ranging 1.94-2.60 eV and 2.95-5.29 eV for the dications and trications, respectively. Experimental measurements are supported by Born-Oppenheimer molecular dynamics (BOMD) simulations.
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| 20. |
- Lee, J. W.L., et al.
(författare)
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Time-resolved relaxation and fragmentation of polycyclic aromatic hydrocarbons investigated in the ultrafast XUV-IR regime
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Polycyclic aromatic hydrocarbons (PAHs) play an important role in interstellar chemistry and are subject to high energy photons that can induce excitation, ionization, and fragmentation. Previous studies have demonstrated electronic relaxation of parent PAH monocations over 10-100 femtoseconds as a result of beyond-Born-Oppenheimer coupling between the electronic and nuclear dynamics. Here, we investigate three PAH molecules: fluorene, phenanthrene, and pyrene, using ultrafast XUV and IR laser pulses. Simultaneous measurements of the ion yields, ion momenta, and electron momenta as a function of laser pulse delay allow a detailed insight into the various molecular processes. We report relaxation times for the electronically excited PAH*, PAH(+*) and PAH(2+*) states, and show the time-dependent conversion between fragmentation pathways. Additionally, using recoil-frame covariance analysis between ion images, we demonstrate that the dissociation of the PAH(2+) ions favors reaction pathways involving two-body breakup and/or loss of neutral fragments totaling an even number of carbon atoms. Polycyclic aromatic hydrocarbons play an important role in interstellar chemistry, where interaction with high energy photons can induce ionization and fragmentation reactions. Here the authors, with XUV-IR pump-probe experiments, investigate the ultrafast photoinduced dynamics of fluorene, phenanthrene and pyrene, providing insight into their preferred reaction channels.
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| 21. |
- Maclot, Sylvain, et al.
(författare)
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Charge and energy flows in ionised thymidine
- 2015
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 635, s. 032072-032072
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Konferensbidrag (refereegranskat)abstract
- We present a combined experimental and theoretical study of the ionisation and fragmentation of the nucleoside thymidine in the gas phase. Two sources of ionisation/excitation are used, namely UV photons and low-energy multiply charged ions, associated with coincidences measurements, respectively photoelectron/photofragment (PEPICO) and fragment/fragment. Coupling these experiments with quantum chemistry calculations, we obtain a complete picture of the fragmentation dynamics, in particular the charge and energy transfers within the molecular edifice.
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| 22. |
- Maclot, Sylvain, et al.
(författare)
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Dissociation dynamics of the diamondoid adamantane upon photoionization by XUV femtosecond pulses
- 2020
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Ingår i: Scientific Reports. - : Nature Research. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- This work presents a photodissociation study of the diamondoid adamantane using extreme ultraviolet femtosecond pulses. The fragmentation dynamics of the dication is unraveled by the use of advanced ion and electron spectroscopy giving access to the dissociation channels as well as their energetics. To get insight into the fragmentation dynamics, we use a theoretical approach combining potential energy surface determination, statistical fragmentation methods and molecular dynamics simulations. We demonstrate that the dissociation dynamics of adamantane dications takes place in a two-step process: barrierless cage opening followed by Coulomb repulsion-driven fragmentation.
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| 23. |
- Maclot, Sylvain, et al.
(författare)
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Photodissociation dynamics of the diamondoid adamantane induced by attosecond XUV pulses
- 2020
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Ingår i: 31st international conference on photonic, electronic and atomic collisions (icpeac xxxi). - : IOP Publishing. ; 1412
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Konferensbidrag (refereegranskat)abstract
- Adamantane is the simplest of the diamondoid molecules, which due to their high stability are of high interest both in astrophysics and nanotechnology. This work investigates the molecular photodissociation after ionization by attosecond XUV pulses. The fragmentation dynamics is inferred by means of velocity map imaging spectrometry, covariance analysis techniques and quantum chemistry calculations.
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| 24. |
- Maclot, Sylvain, et al.
(författare)
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Towards XUV-pump XUV-probe experiments with attosecond pulses at the Lund Laser Centre
- 2015
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 635, s. 112079-112079
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Konferensbidrag (refereegranskat)abstract
- The relaxation dynamics of an ionized/excited molecular system leads to different fundamental processes occurring at sub-femtosecond timescales. Time-resolved XUV-pump XUV-probe experiments should allow deeper insight to the key roles of these processes. Such studies should be feasible soon thanks to experimental schemes similar to those at the high-intensity high-order harmonic generation beamline at the Lund Laser Centre.
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| 25. |
- Malm, Erik, et al.
(författare)
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Singleshot polychromatic coherent diffractive imaging with a high-order harmonic source
- 2020
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Ingår i: Optics Express. - 1094-4087. ; 28:1, s. 394-404
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Tidskriftsartikel (refereegranskat)abstract
- Singleshot polychromatic coherent diffractive imaging is performed with a high-intensity high-order harmonic generation source. The coherence properties are analyzed and several reconstructions show the shot-to-shot fluctuations of the incident beam wavefront. The method is based on a multi-step approach. First, the spectrum is extracted from double-slit diffraction data. The spectrum is used as input to extract the monochromatic sample diffraction pattern, then phase retrieval is performed on the quasi-monochromatic data to obtain the sample's exit surface wave. Reconstructions based on guided error reduction (ER) and alternating direction method of multipliers (ADMM) are compared. ADMM allows additional penalty terms to be included in the cost functional to promote sparsity within the reconstruction.
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