| 1. |
- 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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| 2. |
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| 3. |
- Balla, Prannay, et al.
(författare)
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Post-compression of picosecond pulses to four optical cycles
- 2020
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Ingår i: High Intensity Lasers and High Field Phenomena, HILAS 2020. - 9781557528209
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Konferensbidrag (refereegranskat)abstract
- We report post-compression of 1.2 ps pulses into the few-cycle regime via multi-pass spectral broadening. We achieve compression factors of 40 in single and 93 in a dual stage scheme using a compact setup.
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| 4. |
- Balla, Prannay, et al.
(författare)
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Postcompression of picosecond pulses into the few-cycle regime
- 2020
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Ingår i: Optics Letters. - 0146-9592. ; 45:9, s. 2572-2575
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Tidskriftsartikel (refereegranskat)abstract
- In this work,we demonstrate postcompression of 1.2 ps laser pulses to 13 fs via gas-based multipass spectral broadening. Our results yield a single-stage compression factor of about 40 at 200 W in-burst average power and a total compression factor >90 at reduced power. The employed scheme represents a route toward compact few-cycle sources driven by industrial-grade Yb:YAG lasers at high average power.
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| 5. |
- 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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| 6. |
- 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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| 7. |
- Campi, Filippo, et al.
(författare)
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Design and test of a broadband split-and-delay unit for attosecond XUV-XUV pump-probe experiments.
- 2016
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 87:2
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Tidskriftsartikel (refereegranskat)abstract
- We present the design of a split-and-delay unit for the production of two delayed replicas of an incident extreme ultraviolet (XUV) pulse. The device features a single grazing incidence reflection in combination with attenuation of remaining infrared light co-propagating with the XUV beam, offering a high throughput without the need of introducing additional optics that would further decrease the XUV flux. To achieve the required spatial and temporal stabilities, the device is controlled by two PID-controllers monitoring the delay and the beam pointing using an optical reference laser beam, making collimation of the beam by additional optics unnecessary. Finally, we demonstrate the stability of the split-and-delay unit by performing all-reflective autocorrelation measurements on broadband few-cycle laser pulses.
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| 8. |
- 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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| 9. |
- 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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| 10. |
- Escoto, Esmerando, et al.
(författare)
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Role of dispersion and compression ratio on the temporal contrast of SPM-broadened post-compressed pulses
- 2021
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Ingår i: 2021 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2021. - 9781665418768
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Konferensbidrag (refereegranskat)abstract
- Nonlinear pulse post-compression, mainly enabled by self-phase modulation (SPM), opens new avenues towards high peak power laser pulses at high average power while bypassing the need for a gain medium with large bandwidth. However, SPM-induced spectral broadening typically introduces spectral amplitude modulations as well as a chirp of third and higher orders, limiting the temporal contrast of the compressed pulse. While some recent works address this issue and discuss mitigation strategies [1] , [2] , not much attention has been devoted to the physical processes and limitations that determine the temporal contrast of post-compressed pulses. As novel compression techniques expand the achievable compression ratio [3] , it is increasingly important to fully understand the underlying pulse quality limitations. Here, we outline the role of two important characteristics - dispersion and compression ratio - on the temporal quality of post-compressed pulses. Using both numerical simulations as well as experimental tests employing a gas-filled multi-pass cell (MPC), we study the temporal contrast of post-compressed pulses over large compression-ratio and dispersion range. Using a 730 fs input pulse we were able to generate a 55 fs post-compressed pulse with up to 78% energy contained in the main compressed pulse (defined via the first local minima near the highest peak) against its picosecond background.
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| 11. |
- Forbes, Ruaridh, et al.
(författare)
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Time-resolved site-selective imaging of predissociation and charge transfer dynamics : The CH3I B-band
- 2020
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:22
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Tidskriftsartikel (refereegranskat)abstract
- The predissociation dynamics of the 6s (B2E) Rydberg state of gas-phase CH3I were investigated by time-resolved Coulomb-explosion imaging using extreme ultraviolet (XUV) free-electron laser pulses. Inner-shell ionization at the iodine 4d edge was utilized to provide a site-specific probe of the ensuing dynamics. The combination of a velocity-map imaging (VMI) spectrometer coupled with the pixel imaging mass spectrometry (PImMS) camera permitted three-dimensional ionic fragment momenta to be recorded simultaneously for a wide range of iodine charge states. In accord with previous studies, initial excitation at 201.2 nm results in internal conversion and subsequent dissociation on the lower-lying A-state surface on a picosecond time scale. Examination of the time-dependent yield of low kinetic energy iodine fragments yields mechanistic insights into the predissociation and subsequent charge transfer following multiple ionization of the iodine products. The effect of charge transfer was observed through differing delay-dependencies of the various iodine charge states, from which critical internuclear distances for charge transfer could be inferred and compared to a classical over-the-barrier model. Time-dependent photofragment angular anisotropy parameters were extracted from the central slice of the Newton sphere, without Abel inversion, and highlight the effect of rotation of the parent molecule before dissociation, as observed in previous
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| 12. |
- 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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| 13. |
- 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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| 14. |
- Lever, Fabiano, et al.
(författare)
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Core-level spectroscopy of 2-thiouracil at the sulfur L1 and L2,3-edges utilizing a sase free-electron laser
- 2021
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Ingår i: Molecules. - : MDPI AG. - 1420-3049. ; 26:1
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report X-ray absorption and core-level electron spectra of the nucleobase derivative 2-thiouracil at the sulfur L1-and L2,3-edges. We used soft X-rays from the free-electron laser FLASH2 for the excitation of isolated molecules and dispersed the outgoing electrons with a magnetic bottle spectrometer. We identified photoelectrons from the 2p core orbital, accompanied by an electron correlation satellite, as well as resonant and non-resonant Coster–Kronig and Auger– Meitner emission at the L1-and L2,3-edges, respectively. We used the electron yield to construct X-ray absorption spectra at the two edges. The experimental data obtained are put in the context of the literature currently available on sulfur core-level and 2-thiouracil spectroscopy.
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| 15. |
- 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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| 16. |
- Manschwetus, Bastian, et al.
(författare)
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Self-Probing Spectroscopy of the SF6 Molecule: A Study of the Spectral Amplitude and Phase of the High Harmonic Emission
- 2015
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Ingår i: The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory. - : American Chemical Society (ACS). - 1520-5215. ; 119:23, s. 6111-6122
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Tidskriftsartikel (refereegranskat)abstract
- We present characterizations of the attosecond pulse train produced in the high harmonic generation (HHG) from SF6 molecules irradiated by a strong pulsed laser field at 800 nm. At harmonic order 17, we observe a minimum in the amplitude of the emitted spectrum and a corresponding distortion in the phase. Our experimental results are compared to two models: a multicenter interference model focused on the effect of the structure of the SF6 molecule in HHG and a model focused on the interferences between multiple ionization channels in HHG. We find that the experimental results agree very well with the multiple ionization channels model, illustrating that HHG in molecules can be very complex and that it provides insights of the intramolecular electron dynamics during the interaction process.
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| 17. |
- Schmising, Clemens von Korff, et al.
(författare)
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Element-Specific Magnetization Dynamics of Complex Magnetic Systems Probed by Ultrafast Magneto-Optical Spectroscopy
- 2020
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Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 10:21
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Tidskriftsartikel (refereegranskat)abstract
- The vision to manipulate and control magnetism with light is driven on the one hand by fundamental questions of direct and indirect photon-spin interactions, and on the other hand by the necessity to cope with ever growing data volumes, requiring radically new approaches on how to write, read and process information. Here, we present two complementary experimental geometries to access the element-specific magnetization dynamics of complex magnetic systems via ultrafast magneto-optical spectroscopy in the extreme ultraviolet spectral range. First, we employ linearly polarized radiation of a free electron laser facility to demonstrate decoupled dynamics of the two sublattices of an FeGd alloy, a prerequisite for all-optical magnetization switching. Second, we use circularly polarized radiation generated in a laboratory-based high harmonic generation setup to show optical inter-site spin transfer in a CoPt alloy, a mechanism which only very recently has been predicted to mediate ultrafast metamagnetic phase transitions.
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| 18. |
- Varvarezos, Lazaros, et al.
(författare)
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Intensity-dependent near-threshold ionization of Kr in the vacuum-uv
- 2019
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Ingår i: International Conference on Spectral Lines Shapes. - : IOP Publishing. - 1742-6588. ; 1289
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Konferensbidrag (refereegranskat)abstract
- In this work, we present measurements of the intensity-dependent photoelectron spectrum of Kr irradiated by the FLASH FEL tuned to a photon energy of 25.8 eV. Intensity dependent photoelectron spectra were obtained with the aid of a Velocity Map Imaging (VMI) spectrometer. As the FEL photon energy is close to threshold, two photon sequential double ionization is favoured. The number of open channels is kept to a minimum and leading to a simple description of the process.
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| 19. |
- Varvarezos, Lazaros, et al.
(författare)
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Near-threshold two-photon double ionization of Kr in the vacuum ultraviolet
- 2021
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Ingår i: Physical Review A. - 2469-9926. ; 103:2
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Tidskriftsartikel (refereegranskat)abstract
- We report angle-resolved measurements on photoelectrons emitted upon near-threshold two-photon double ionization (TPDI) of Kr irradiated by free-electron laser (FEL) pulses. These photoelectron angular distributions (PADs) are compared with the results of semirelativistic R-matrix calculations. As reported by Augustin et al. [Phys. Rev. A 98, 033408 (2018)10.1103/PhysRevA.98.033408], it is found that the presence of autoionizing resonances within the bandwidth of the exciting FEL pulse strongly influences the PADs. In contrast to measurements on lower-Z targets such as Ne and Ar, the larger spin-orbit interaction, inherent in 4p-subshell hole states of Kr, permits us to resolve and study PADs associated with some of the fine-structure components of the Kr+ and Kr2+ ions.
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| 20. |
- Viotti, Anne Lise, et al.
(författare)
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60 fs, 1030 nm FEL pump-probe laser based on a multi-pass post-compressed Yb:YAG source
- 2021
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495. ; 28, s. 36-43
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on nonlinear spectral broadening of 1.1 ps pulses in a gas-filled multi-pass cell to generate sub-100 fs optical pulses at 1030 nm and 515 nm at pulse energies of 0.8 mJ and 225 μJ, respectively, for pump-probe experiments at the free-electron laser FLASH. Combining a 100 kHz Yb:YAG laser with 180 W in-burst average power and a post-compression platform enables reaching simultaneously high average powers and short pulse durations for high-repetition-rate FEL pump-probe experiments.
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| 21. |
- Viotti, Anne Lise, et al.
(författare)
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Intra-Burst Pulse Characterization of a High-Power Post-Compressed Yb:YAG Laser at 100 kHz Repetition Rate
- 2021
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Ingår i: 2021 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2021. - 9781665418768
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Konferensbidrag (refereegranskat)abstract
- High-average power Ytterbium (Yb) laser systems are playing an increasingly important role in ultrafast science e.g. as pump lasers for optical parametric amplifiers or directly as ultrafast sources. The gain bandwidth of Yb limits the pulse duration to a few 100 fs up to about 1 ps. However, many applications, such as attosecond physics or X-ray Free Electron Laser (FEL) science, would greatly benefit from the combination of high average powers with much shorter pulses, achievable via post-compression. Nonlinear pulse post-compression of high-average power Yb lasers employing multi-pass cell (MPC) -based spectral broadening [1], [2] was recently implemented for two burst-mode pump-probe lasers at the FEL facility FLASH in Hamburg [3], [4]. For such lasers, precise characterization and control of intra-burst pulse dynamics is crucial as the post-compression process couples input pulse energy instabilities with important output pulse parameters such as spectrum, pulse length and temporal contrast. Here, we demonstrate 100 kHz intra-burst spectrum, phase and temporal contrast characterization of a Yb:YAG Innoslab burst-mode amplifier post-compressed in a gas-filled MPC. Our measurements reveal a stable broadened spectrum and compressed pulse duration within the flat part of the burst, yielding a relative energy content of about 80% in the main compressed fs pulse (250 fs window versus 4 ps background pedestal).
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| 22. |
- Viotti, Anne Lise, et al.
(författare)
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Intra-burst temporal pulse contrast of a high-power post-compressed picosecond Yb:YAG laser
- 2021
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Ingår i: Conference on Laser and Electro-Optics : Science and Innovations, CLEO:S and I 2021 - Science and Innovations, CLEO:S and I 2021. - 9781557528209
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Konferensbidrag (refereegranskat)abstract
- We report on pulse contrast characterization of the output of a gas-filled multi-pass cell employed for 20-fold compression of a high-power Yb:YAG laser. We demonstrate an energy content of 80% in the compressed fs pulse.
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