| 1. |
- Arnold, Cord L., et al.
(författare)
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A high-repetition rate attosecond pulse source for coincidence spectroscopy
- 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
- The power of attosecond pump-probe spectroscopy combined with advanced detection schemes, such as photoelectron/ion coincidence spectrometers and time-resolved photoelectron emission microscopy (PEEM), can be unleashed by properly accounting for the repetition rate of the source. In this work, we present a high-repetition rate (200 kHz) attosecond pulse source that opens up for exploring phenomena, previously inaccessible to the community using attosecond interferometric and spectroscopy pump-probe techniques [1].
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| 2. |
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| 3. |
- Laurell, Hugo, et al.
(författare)
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Measuring the quantum state of photoelectrons
- 2023
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A photoelectron, emitted due to the absorption of light quanta as described by the photoelectric effect, is often characterized experimentally by a classical quantity, its momentum. However, since the photoelectron is a quantum object, its rigorous characterization requires the reconstruction of the complete quantum state, the photoelectron's density matrix. Here, we use quantum state tomography to fully characterize photoelectrons emitted from helium and argon atoms upon absorption of ultrashort, extreme ultraviolet light pulses. While in helium we measure a pure photoelectronic state, in argon, spin-orbit interaction induces entanglement between the ion and the photoelectron, leading to a reduced purity of the photoelectron state. Our work shows how state tomography gives new insights into the fundamental quantum aspects of light-induced electronic processes in matter, bridging the fields of photoelectron spectroscopy and quantum information, and offering new spectroscopic possibilities for quantum technology.
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| 4. |
- Luo, Sizuo, et al.
(författare)
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Ultra-stable and versatile high-energy resolution setup for attosecond photoelectron spectroscopy
- 2023
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Ingår i: Advances in Physics: X. - 2374-6149. ; 8:1
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Forskningsöversikt (refereegranskat)abstract
- Attosecond photoelectron spectroscopy has opened up for studying light–matter interaction on ultrafast time scales. It is often performed with interferometric experimental setups that require outstanding stability. We demonstrate and characterize in detail an actively stabilized, versatile, high spectral resolution attosecond beamline based on a Mach-Zehnder interferometer. The active stabilization keeps the interferometer ultra-stable for several hours with an RMS stability of 13 as and a total pump-probe delay scanning range of (Formula presented.) fs. A tunable femtosecond laser source to drive high-order harmonic generation allows for precisely addressing atomic and molecular resonances. Furthermore, the interferometer includes a spectral shaper in 4f-geometry in the probe arm as well as a tunable bandpass filter in the pump arm, which offer additional high flexibility in terms of tunability as well as narrowband or polychromatic probe pulses. We demonstrate the capabilities of the beamline via experiments using several variants of the RABBIT (reconstruction of attosecond beating by two photon transitions) technique. In this setup, the temporal-spectral resolution of photoelectron spectroscopy can reach a new level of accuracy and precision.
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| 5. |
- Mikaelsson, Sara, et al.
(författare)
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A high-repetition rate attosecond light source for time-resolved coincidence spectroscopy
- 2020
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Ingår i: Nanophotonics. - : Walter de Gruyter GmbH. - 2192-8614 .- 2192-8606. ; 10:1, s. 117-128
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Tidskriftsartikel (refereegranskat)abstract
- Attosecond pulses, produced through high-order harmonic generation in gases, have been successfully used for observing ultrafast, subfemtosecond electron dynamics in atoms, molecules and solid state systems. Today's typical attosecond sources, however, are often impaired by their low repetition rate and the resulting insufficient statistics, especially when the number of detectable events per shot is limited. This is the case for experiments, where several reaction products must be detected in coincidence, and for surface science applications where space charge effects compromise spectral and spatial resolution. In this work, we present an attosecond light source operating at 200 kHz, which opens up the exploration of phenomena previously inaccessible to attosecond interferometric and spectroscopic techniques. Key to our approach is the combination of a high-repetition rate, few-cycle laser source, a specially designed gas target for efficient high harmonic generation, a passively and actively stabilized pump-probe interferometer and an advanced 3D photoelectron/ion momentum detector. While most experiments in the field of attosecond science so far have been performed with either single attosecond pulses or long trains of pulses, we explore the hitherto mostly overlooked intermediate regime with short trains consisting of only a few attosecond pulses. We also present the first coincidence measurement of single-photon double-ionization of helium with full angular resolution, using an attosecond source. This opens up for future studies of the dynamic evolution of strongly correlated electrons.
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| 6. |
- Mikaelsson, Sara, et al.
(författare)
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A high-repetition rate attosecond light source for time-resolved coincidence spectroscopy
- 2021
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Ingår i: Frontiers in Optics and Photonics. - : De Gruyter. - 9783110710687 - 9783110709735 ; , s. 119-130
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Bokkapitel (refereegranskat)abstract
- Attosecond pulses, produced through high-order harmonic generation in gases, have been successfully used for observing ultrafast, subfemtosecond electron dynamics in atoms, molecules and solid state systems. Today's typical attosecond sources, however, are often impaired by their low repetition rate and the resulting insufficient statistics, especially when the number of detectable events per shot is limited. This is the case for experiments, where several reaction products must be detected in coincidence, and for surface science applications where space charge effects compromise spectral and spatial resolution. In this work, we present an attosecond light source operating at 200 kHz, which opens up the exploration of phenomena previously inaccessible to attosecond interferometric and spectroscopic techniques. Key to our approach is the combination of a high-repetition rate, few-cycle laser source, a specially designed gas target for efficient high harmonic generation, a passively and actively stabilized pump-probe interferometer and an advanced 3D photoelectron/ion momentum detector. While most experiments in the field of attosecond science so far have been performed with either single attosecond pulses or long trains of pulses, we explore the hitherto mostly overlooked intermediate regime with short trains consisting of only a few attosecond pulses. We also present the first coincidence measurement of single-photon dou-ble-ionization of helium with full angular resolution, using an attosecond source. This opens up for future studies of the dynamic evolution of strongly correlated electrons.
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| 7. |
- Weissenbilder, Robin, et al.
(författare)
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Choice of an efficient gas target for high-order harmonic generation
- 2021
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Ingår i: Conference on Lasers 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 present a simple method for choosing an efficient h igh-order harmonic generation (HHG) gas target, given the driving laser characteristics. The predictions are validated by simulations based on solving the time-dependent Schrödinger and propagation equations.
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| 8. |
- Weissenbilder, Robin, et al.
(författare)
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Hyperbolic trend in optimization of high-order harmonic generation in gases
- 2023
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Ingår i: 2023 Conference on Lasers and Electro-Optics, CLEO 2023. - 9781957171258
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Konferensbidrag (refereegranskat)abstract
- We demonstrate, using analytic models, simulations and experiments, that efficient generation of high-order harmonics is possible across a large range of parameters, if the density and medium length follow a hyperbolic equation.
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| 9. |
- Weissenbilder, Robin
(författare)
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Optimization of High-order Harmonic Generation for Attosecond Science
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-order harmonic generation is a highly nonlinear, though inherently inefficient, process which can lead to emission of coherent, broadband extreme ultraviolet radiation in the form of attosecond pulses. Attosecond pulses are crucial for experiments investigating photoionization dynamics on the femto- and attosecond timescales. As attosecond research tends towards increasingly complex light-matter interactions, demands on high flux attosecond sources grow. This thesis deals with light-matter interactions in the non-perturbative and perturbative regimes. Optimal generation of high-order harmonics in gases is studied, and the attosecond pulses are applied in two-photon pump-probe photoelectron interferometry schemes to unravel photoionization dynamics on the intrinsic timescales of the electron.The first part of this thesis focuses on optimization of the conversion efficiency in high-order harmonic generation in gases, with emphasis on macroscopic phase-matching effects. We explain the large variety of gas target designs in the literature through an analytic model. The model predicts, independently of the driving laser focusing geometry, that efficient high-order harmonic generation is possible for a wide range of densities and medium lengths, if these follow a hyperbolic relation. The model suggests the existence of two phase-matching regimes with similar efficiency but different spatial and temporal characteristics of the emitted extreme ultraviolet radiation. We verify the model for a wide range of generation parameters experimentally and using numerical simulations.The second part of this thesis concerns the application of attosecond pulse trains, consisting of high-order harmonics, to infer information about electron correlations in atoms. Photoionization dynamics occurring on the femto- and attosecond timescales are probed by measuring the amplitude and phase of oscillations in the photoelectron signal, induced by path interference of two-photon transitions. Two interference techniques are used: First, Reconstruction of Attosecond Beatings By Interference of Two-photon transitions (RABBIT) is used to study (i) photonionization time delays across the 4d giant dipole resonance in xenon, (ii) resonant below-threshold two-photon ionization of the 1s3p, 1s4p and 1s5p Rydberg states in helium and (iii) autoionization dynamics from the 3s13p64p Fano resonance in argon. Secondly, to fully characterize mixed photoelectron quantum states, a quantum state tomography protocol for photoelectrons (KRAKEN) is developed theoretically and tested experimentallyfor non-resonant photoionization of helium and argon.
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| 10. |
- Zhong, Shiyang, et al.
(författare)
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Attosecond electron–spin dynamics in Xe 4d photoionization
- 2020
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- The photoionization of xenon atoms in the 70–100 eV range reveals several fascinating physical phenomena such as a giant resonance induced by the dynamic rearrangement of the electron cloud after photon absorption, an anomalous branching ratio between intermediate Xe+ states separated by the spin-orbit interaction and multiple Auger decay processes. These phenomena have been studied in the past, using in particular synchrotron radiation, but without access to real-time dynamics. Here, we study the dynamics of Xe 4d photoionization on its natural time scale combining attosecond interferometry and coincidence spectroscopy. A time-frequency analysis of the involved transitions allows us to identify two interfering ionization mechanisms: the broad giant dipole resonance with a fast decay time less than 50 as, and a narrow resonance at threshold induced by spin-flip transitions, with much longer decay times of several hundred as. Our results provide insight into the complex electron-spin dynamics of photo-induced phenomena.
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