| 1. |
- 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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| 2. |
- Adrian-Martinez, S., et al.
(författare)
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The First Combined Search For Neutrino Point-Sources In The Southern Hemisphere With The Antares And Icecube Neutrino Telescopes
- 2016
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 823:1
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of searches for point-like sources of neutrinos based on the first combined analysis of data from both the ANTARES and IceCube neutrino telescopes. The combination of both detectors, which differ in size and location, forms a window in the southern sky where the sensitivity to point sources improves by up to a factor of 2 compared with individual analyses. Using data recorded by ANTARES from 2007 to 2012, and by IceCube from 2008 to 2011, we search for sources of neutrino emission both across the southern sky and from a preselected list of candidate objects. No significant excess over background has been found in these searches, and flux upper limits for the candidate sources are presented for E-2.5 and E-2 power-law spectra with different energy cut-offs.
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| 3. |
- Bertolino, Mattias, et al.
(författare)
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Propensity rules and interference effects in laser-Assisted photoionization of helium and neon
- 2020
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:14
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the angle-resolved photoelectron spectra from laser-Assisted photoionization for helium and neon atoms using an ab initio method based on time-dependent surface flux and configuration interaction singles. We find that the shape of the distributions can be interpreted using a propensity rule, an intrinsic difference in the absorption and the emission processes, as well as interference effects between multiple paths to the final angular momentum state. The difference between absorption and emission is hidden in the first sideband in neon due to the multiple competing m channels, while in the second sideband a qualitative difference between absorption and emission is observed. In the m-resolved case, a clear difference is observed already in the first sideband, as exemplified in helium and m-resolved neon.
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| 4. |
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| 5. |
- 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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| 6. |
- Busto, David, et al.
(författare)
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Probing electronic decoherence with high-resolution attosecond photoelectron interferometry
- 2022
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Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 76:7
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Quantum coherence plays a fundamental role in the study and control of ultrafast dynamics in matter. In the case of photoionization, entanglement of the photoelectron with the ion is a well-known source of decoherence when only one of the particles is measured. Here, we investigate decoherence due to entanglement of the radial and angular degrees of freedom of the photoelectron. We study two-photon ionization via the 2s2p autoionizing state in He using high spectral resolution photoelectron interferometry. Combining experiment and theory, we show that the strong dipole coupling of the 2s2p and 2p2 states results in the entanglement of the angular and radial degrees of freedom. This translates, in angle-integrated measurements, into a dynamic loss of coherence during autoionization. Graphic Abstract: [Figure not available: see fulltext.]. © 2022, The Author(s).
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| 7. |
- Busto, David
(författare)
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Quantum interference effects in attosecond photoionization dynamics
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The interaction of extreme ultraviolet light with matter can lead to the emission of an electron in a process known as photoionization. The electron wavepacket (EWP) created in the continuum propagates on the ionic potential, resulting in a delay compared to an EWP propagating freely. The development of extreme ultraviolet attosecond light sources in recent years has opened the possibility to probe photoionization on the attosecond time scale ($10^{-18}$~s).In this thesis, atomic photoionization is investigated in both resonant and non-resonant conditions via the attosecond photoelectron interferometric technique RABBIT (Reconstruction of Attosecond Beating By Interference of Two-photon transitions). Atoms are photoionized by an attosecond pulse train (APT), creating an EWP in the continuum. The EWP is then made to interfere with itself using a weak delayed infrared (IR) probe pulse. Recording the photoelectron signal as a function of the delay between the IR and the APT allows us to characterize the EWP in the spectral domain.In this thesis we investigate experimentally and theoretically photoionization dynamics in various atoms (He, Ne, Ar and Xe) as well as in the N$_2$ molecule. These studies focus on understanding how the presence of multiple ionization channels affects the ionization dynamics. On the one hand, we study the situation in which different ionization channels are excited incoherently resulting in overlapping photoelectron peaks in the spectrum. In this case, we show that the RABBIT technique allows us to measure photoionization time delays with a few tens of attosecond resolution while maintaining the high spectral resolution needed to disentangle contributions from different ionization channels. On the other hand, we investigate the case where several ionization channels are excited coherently leading to interference between different quantum paths. Using the RABBIT technique, we study the interference between direct photoionization and autoionization in the vicinity of Fano resonances. Measuring the amplitude and phase of photoelectrons emitted via these resonances, we characterize the EWPs in time-frequency domain. By pushing the spectral resolution of our measurements we are able to observe signatures of quantum decoherence and to quantify it. In addition, using angle-resolved measurements, we investigate the effect of the coherent superposition of final states with different angular momenta. We show that it results in angular interference which lead to an angle-dependence of the photoionization time delays and to a modification of the photoelectron angular distribution with pump-probe delay.
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| 8. |
- Ertel, Dominik, et al.
(författare)
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Anisotropy Parameters for Two-Color Photoionization Phases in Randomly Oriented Molecules : Theory and Experiment in Methane and Deuteromethane
- 2024
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Ingår i: Journal of Physical Chemistry A. - 1089-5639 .- 1520-5215. ; 128:9, s. 1685-1697
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Tidskriftsartikel (refereegranskat)abstract
- We present combined theoretical and experimental work investigating the angle-resolved phases of the photoionization process driven by a two-color field consisting of an attosecond pulse train and an infrared pulse in an ensemble of randomly oriented molecules. We derive a general form for the two-color photoelectron (and time-delay) angular distribution valid also in the case of chiral molecules and when relative polarizations of the photons contributing to the attosecond photoelectron interferometer differ. We show a comparison between the experimental data and theoretical predictions in an ensemble of methane and deuteromethane molecules, discussing the effect of nuclear dynamics on the photoionization phases. Finally, we demonstrate that the oscillating component and the phase of the two-color signal can be fitted by using complex asymmetry parameters, in perfect analogy to the atomic case.
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| 9. |
- Ertel, Dominik, et al.
(författare)
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Influence of nuclear dynamics on molecular attosecond photoelectron interferometry
- 2023
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Ingår i: Science Advances. - 2375-2548. ; 9:35
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Tidskriftsartikel (refereegranskat)abstract
- In extreme ultraviolet spectroscopy, the photoionization process occurring in a molecule due to the absorption of a single photon can trigger an ultrafast nuclear motion in the cation. Taking advantage of attosecond photoelectron interferometry, where the absorption of the extreme ultraviolet photon is accompanied by the exchange of an additional infrared quantum of light, one can investigate the influence of nuclear dynamics by monitoring the characteristics of the photoelectron spectra generated by the two-color field. Here, we show that attosecond photoelectron interferometry is sensitive to the nuclear response by measuring the two-color photoionization spectra in a mixture of methane (CH4) and deuteromethane (CD4). The effect of the different nuclear evolution in the two isotopologues manifests itself in the modification of the amplitude and contrast of the oscillations of the photoelectron peaks. Our work indicates that nuclear dynamics can affect the coherence properties of the electronic wave packet emitted by photoionization on a time scale as short as a few femtoseconds.
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| 10. |
- Maroju, Praveen Kumar, et al.
(författare)
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Attosecond coherent control of electronic wave packets in two-colour photoionization using a novel timing tool for seeded free-electron laser
- 2023
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Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 17, s. 200-207
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Tidskriftsartikel (refereegranskat)abstract
- In ultrafast spectroscopy, the temporal resolution of time-resolved experiments depends on the duration of the pump and probe pulses, and on the control and characterization of their relative synchronization. Free-electron lasers operating in the extreme ultraviolet and X-ray spectral regions deliver pulses with femtosecond and attosecond duration in a broad array of pump-probe configurations to study a wide range of physical processes. However, this flexibility, together with the large dimensions and high complexity of the experimental set-ups, limits control of the temporal delay to the femtosecond domain, thus precluding a time resolution below the optical cycle. Here we demonstrate a novel single-shot technique able to determine the relative synchronization between an attosecond pulse train-generated by a seeded free-electron laser-and the optical oscillations of a near-infrared field, with a resolution of one atomic unit (24 as). Using this attosecond timing tool, we report the first example of attosecond coherent control of photoionization in a two-colour field by manipulating the phase of high-order near-infrared transitions.
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