Investigating two-photon double ionization ofD2by XUV-pump–XUV-probe experiments (original) (raw)
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Physical Review A, 2010
Two-photon double ionization (TPDI) of D 2 is studied for 38-eV photons at the Free Electron Laser in Hamburg (FLASH). Based on model calculations, instantaneous and sequential absorption pathways are identified as separated peaks in the measured D + + D + fragment kinetic energy release (KER) spectra. The instantaneous process appears at high KER, corresponding to ionization at the molecule's equilibrium distance, in contrast to sequential ionization mainly leading to low-KER contributions. Measured fragment angular distributions are in good agreement with theory.
Electronic correlations in double ionization of atoms in pump-probe experiments
EPL (Europhysics Letters), 2010
The ionization dynamics of a two-electron atom in an attosecond XUV-infrared pump-probe experiment is simulated by solving the time-dependent two-electron Schrödinger equation. A dramatic change of the double ionization (DI) yield with variation of the pumpprobe delay is reported and the governing role of electron-electron correlations is shown. The results allow for a direct control of the DI yield and of the relative strength of double and single ionization.
Signatures of direct double ionization under xuv radiation
Physical Review A - Atomic, Molecular, and Optical Physics, 2005
In anticipation of upcoming two-photon double ionization of atoms and particularly Helium, under strong short wavelength radiation sources (45 eV), we present quantitative signatures of direct twophoton double ejection, in the photoelectron spectrum (PES) and the peak power dependence, that can be employed in the interpretation of related data. We show that the PES provides the cleanest signature of the process. An inflection (knee) in the laser power dependence of double ionization is also discernible, within a window of intensities which depends on the pulse duration and cross sections PACS numbers: 32.80.Wr
Double ionization probed on the attosecond timescale
Nature Physics, 2014
Double ionization following the absorption of a single photon is one of the most fundamental processes requiring interaction between electrons 1-3. Information about this interaction is usually obtained by detecting emitted particles without access to real-time dynamics. Here, attosecond light pulses 4,5 , electron wave packet interferometry 6 and coincidence techniques 7 are combined to measure electron emission times in double ionization of xenon using single ionization as a clock, providing unique insight into the two-electron ejection mechanism. Access to many-particle dynamics in real time is of fundamental importance for understanding processes induced by electron correlation in atomic, molecular and more complex systems. The emergence of attosecond science (1 as = 10 −18 s) in the new millennium opened an exciting area of physics bringing the dynamics of electron wave functions into focus. The important goal of real-time visualization of the interplay between electrons and their role in molecular bonding now seems to be in reach. After a decade where attosecond light sources 4,5 were characterized and their potential demonstrated, the next phase will include the exploration of correlated electron dynamics in complex systems. A series of groundbreaking studies on single ionization (SI) in atoms using attosecond light pulses sheds light on the escaping electron and its interaction with the residual ion 6,8 , and the resulting coherent superposition of neutral bound states 9,10. Double ionization (DI) by absorption of a single photon is an inherently more challenging phenomenon, both experimentally and theoretically 1-3. The two-electron ejection can be understood only through interactions between electrons, and is usually discussed in terms of different mechanisms 11. In the knockout mechanism, the electron excited by interaction with the light field (the photoelectron) collides with another electron on its way out, resulting in two emitted electrons. In the shake-off mechanism, orbital relaxation following the creation of a hole ionizes a second electron. Electron correlations may also lead to indirect DI processes via highly excited states of the singly-charged ion 12. One-photon experimental investigations with the pair of electrons detected in coincidence can provide a fairly complete DI description without, however, following the dynamics of the electron correlation in real time. Multiphoton experimental investigations have been performed both on the femtosecond and attosecond timescales 13,14 , but DI in strong laser fields does not require electron correlation. In this work, we study DI of xenon in the near-threshold region using attosecond extreme ultraviolet (XUV) pulses for excitation
Two-color photoionization in xuv free-electron and visible laser fields
Physical Review A, 2006
Two-photon ionization of atomic helium has been measured by combining femtosecond extreme-ultraviolet pulses from the free-electron laser in Hamburg ͑FLASH at DESY͒ with intense light pulses from a synchronized neodymium-doped yttrium lithium fluoride laser. Sidebands appear in the photoelectron spectra when the two laser pulses overlap in both space and time. Their intensity exhibits a characteristic dependence on the relative time delay between the ionizing and the dressing pulses and provides an inherent time marker for time-resolved pump-probe experiments. The measurements of the sidebands are in good agreement with theoretical predictions and allow for a direct analysis of two-photon ionization, free from processes related to interference between multiple quantum paths.
Attosecond timescale analysis of the dynamics of two-photon double ionization of helium
New Journal of Physics, 2008
We consider the two-photon double ionization (DI) of helium and analyze electron dynamics on the attosecond timescale. We first re-examine the interaction of helium with an ultrashort XUV pulse and study how the electronic correlations affect the electron angular and energy distributions in the direct, sequential and transient regimes of frequency and time duration. We then consider pump-probe processes with the aim of extracting indirect information on the pump pulse. In addition, our calculations show clear evidence for the existence under certain conditions of direct two-color DI processes.
Using a new experimental method, physicists from the Max Planck Institute for Nuclear Physics in Heidelberg investigated the resonant two-photon ionization of helium with improved spectral resolution and angular resolution. [34]
Journal of Physics: Conference Series, 2010
We consider two-photon double ionization of helium by two xuv photons in the region around the sequential ionization threshold. We show that, on the attosecond timescale, the mechanism for double ionization is dominated by the absorption of one photon by each electron in the fundamental state He(1s 2 ). We examine the dynamics of two-photon double ionization of helium for an averaged photon energy ω =50 eV, with a pulse duration of two optical cycles. The double ionization rate, energy and angular distributions are calculated by solving the time-dependent Schrödinger equation. Results are discussed on the basis of a model.
Jitter-correction for IR/UV-XUV pump-probe experiments at the FLASH free-electron laser
New Journal of Physics, 2017
In pump-probe experiments employing a free-electron laser (FEL) in combination with a synchronized optical femtosecond laser, the arrival-time jitter between the FEL pulse and the optical laser pulse often severely limits the temporal resolution that can be achieved. Here, we present a pump-probe experiment on the UV-induced dissociation of 2,6-difluoroiodobenzene (C 6 H 3 F 2 I) molecules performed at the FLASH FEL that takes advantage of recent upgrades of the FLASH timing and synchronization system to obtain high-quality data that are not limited by the FEL arrival-time jitter. We discuss in detail the necessary data analysis steps and describe the origin of the timedependent effects in the yields and kinetic energies of the fragment ions that we observe in the experiment.