Two-Photon Ionization of He through a Superposition of Higher Harmonics

Papadogiannis, N. A.; Nikolopoulos, L. A. A.; Charalambidis, D.; Tsakiris, George D.; Tzallas, P.; Witte, Klaus

doi:10.1103/physrevlett.90.133902

Cited by 89 publications

(27 citation statements)

References 23 publications

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“…The very first results were reported in breakthrough experiments at the very limit of intensities that can be obtained with these high-order harmonic sources. These included two-photon single and double ionization of He [4][5][6] and single ionization of the valence shells of Ar and Xe [7]. However, in focused beams, FLASH yields irradiance levels which can approach 10 16 W cm À2 [8], and so it provides a platform for a dramatic expansion of the range of sequential and simultaneous multiphoton ionization experiments that could be performed at EUV wavelengths.…”

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Two-Photon Inner-Shell Ionization in the Extreme Ultraviolet

et al. 2010

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We have observed the simultaneous inner-shell absorption of two extreme-ultraviolet photons by a Xe atom in an experiment performed at the short-wavelength free electron laser facility FLASH. Photoelectron spectroscopy permitted us to unambiguously identify a feature resulting from the ionization of a single electron of the 4d subshell of Xe by two photons each of energy ð93 AE 1Þ eV. The feature's intensity has a quadratic dependence on the pulse energy. The results are discussed and interpreted within the framework of recent results of ion spectroscopy experiments of Xe obtained at ultrahigh irradiance in the extreme-ultraviolet regime. DOI: 10.1103/PhysRevLett.105.013001 PACS numbers: 32.80.Rm, 32.80.Fb, 32.80.Hd, 42.50.Hz The advent of high-intensity extreme-ultraviolet (EUV) and x-ray free electron lasers (FELs) has heralded a new era in the study of nonlinear optical processes. These facilities put this well established area into a new domain where the optical field exhibits a high degree of coherence in addition to an unprecedented combination of high average and peak intensity at high photon energy. As a result, inner-shell electrons and, indeed, highly correlated multielectron excited states can become important mediators of the multiphoton-matter interaction. Since it began operation in 2005, the EUV Free Electron Laser in Hamburg (FLASH) [1] has hosted a wide range of investigations in atomic and molecular physics including experiments on dilute targets such as molecular ions and highly charged ion beams, few-photon few-electron ionization processes, two-color coherent processes, and ultrafast pump-probe experiments [2,3].The simplest nonlinear process one can drive in an intense EUV laser field is two-photon ionization. Consequently, it is a prototypical process and its pursuit has become an important benchmark experiment for the study of the response of the simplest quantum systems, ranging from atoms to clusters, to intense high-frequency electromagnetic fields. Some years ago, high-order harmonic sources developed to the point where they could attain the threshold intensities needed to drive two-photon processes in an atom. The very first results were reported in breakthrough experiments at the very limit of intensities that can be obtained with these high-order harmonic sources. These included two-photon single and double ionization of He [4][5][6] and single ionization of the valence shells of Ar and Xe [7]. However, in focused beams, FLASH yields irradiance levels which can approach 10 16 W cm À2 [8], and so it provides a platform for a dramatic expansion of the range of sequential and simultaneous multiphoton ionization experiments that could be performed at EUV wavelengths. A good example is an experiment where FLASH permitted the full kinematics of two-photon double ionization of the valence shell of Ne to be recorded by using the cold target recoil ion momentum spectroscopy technique [9].Exceptional behavior of the light-matter interaction at high irradiance has been demonstrated in two...

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Two-Photon Inner-Shell Ionization in the Extreme Ultraviolet

et al. 2010

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“…Nonlinear (NL) XUV processes constitute the ideal tool for the study of such dynamics. Attosecond pulse trains 7-9 have reached intensities sufficient to induce two-XUV-photon processes [10][11][12][13][14] . However, isolated attosecond pulses, requisite for XUV-pump-XUV-probe experiments, have not yet attained the required parameters for an observable two-XUV-photon process.…”

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Extreme-ultraviolet pump–probe studies of one-femtosecond-scale electron dynamics

et al. 2011

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Ultrafast-dynamics studies and femtosecond-pulse metrology both rely on the nonlinear processes induced solely by an incident light pulse. Extending these approaches to the extreme-ultraviolet (XUV) spectral region would open up a new route to attosecond-scale dynamics. However, this has been hindered by the limited intensities available in coherent XUV continua. In the present work, we realized conditions at which simultaneous ejection of two bound electrons by two-XUVphoton absorption becomes more efficient than their removal one-by-one. In this regime we have succeeded in tracing atomic coherences evolving at the 1-fs scale with simultaneous determination of the average XUV-pulse duration. The rich and dense structure of the autoionizing manifold demonstrates the applicability of the approach to complex systems. This initiates the era of XUV-pump-XUV-probe experiments at the boundary between femto-and attosecond scales.A large variety of ultrafast phenomena, including electronic motion in atoms, molecules, condensed matter and plasmas, dynamic electron-electron correlations, charge migration, ultrafast dissociation and reaction processes, occur on the few-femtosecond to attosecond temporal scale. Attosecond (as) pulses 1 provide access to these temporal regimes in different states of matter [2][3][4][5][6] . Nonlinear (NL) XUV processes constitute the ideal tool for the study of such dynamics. Attosecond pulse trains 7-9 have reached intensities sufficient to induce two-XUV-photon processes [10][11][12][13][14] . However, isolated attosecond pulses, requisite for XUV-pump-XUV-probe experiments, have not yet attained the required parameters for an observable two-XUV-photon process. As a consequence, attosecond pulse metrology and time-domain applications have been widely based on infrared (IR)-XUV cross-correlation approaches, which entail assumptions for the analysis 15 .The present work succeeds for the first time in observing two-XUV-photon processes induced by energetic XUV continua, in part temporally confined in isolated pulses with durations on the order of 1 fs. These processes are in turn exploited in XUVpump-XUV-probe ultrafast evolving atomic coherences, as well as in determining the duration of the XUV bursts. A structured part of the single continuum of the xenon atom is excited by the first pulse, forming an electronic wave packet that undergoes rapid and complex motion before it decays. This evolution can be traced, thanks to the XUV parameters reached, at which a second pulse ejects a second electron before the first one leaves the atom carrying with it all the information on the temporal evolution of the system (coherence decay). Unconventionally, the two electrons leave the atom together and, thus, the doubly ionized Xe yield as a function of the delay between the two pulses carries the fingerprint of the wave packet motion and the XUV pulse duration. As the pulse duration and the decay The intense XUV radiation is generated by frequency upconversion of many-cycle high-peak-power laser fields...

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“…In particular (i) new combinations of asec delay lines and focusing elements have to be introduced, such as the recently set up of the Lund group [52] and (ii) new non-linear processes have to be considered allowing the application of the method at higher photon energies. So far the two photon ionization of He [43] and N 2 [186] that have been used are not applicable at higher photon energies because the target will be single photon ionized. Candidate processes for this extension are two-photon multiple ionization [156] and two-photon ATI [92].…”

Section: Conclusion and Ongoing Development On Gas-phase And Solid-smentioning

confidence: 99%

Generation of Attosecond Light Pulses from Gas and Solid State Media

et al. 2017

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Real-time observation of ultrafast dynamics in the microcosm is a fundamental approach for understanding the internal evolution of physical, chemical and biological systems. Tools for tracing such dynamics are flashes of light with duration comparable to or shorter than the characteristic evolution times of the system under investigation. While femtosecond (fs) pulses are successfully used to investigate vibrational dynamics in molecular systems, real time observation of electron motion in all states of matter requires temporal resolution in the attosecond (1 attosecond (asec) = 10 −18 s) time scale. During the last decades, continuous efforts in ultra-short pulse engineering led to the development of table-top sources which can produce asec pulses. These pulses have been synthesized by using broadband coherent radiation in the extreme ultraviolet (XUV) spectral region generated by the interaction of matter with intense fs pulses. Here, we will review asec pulses generated by the interaction of gas phase media and solid surfaces with intense fs IR laser fields. After a brief overview of the fundamental process underlying the XUV emission form these media, we will review the current technology, specifications and the ongoing developments of such asec sources.

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Two-Photon Ionization of He through a Superposition of Higher Harmonics

Cited by 89 publications

References 23 publications

Two-Photon Inner-Shell Ionization in the Extreme Ultraviolet

Two-Photon Inner-Shell Ionization in the Extreme Ultraviolet

Extreme-ultraviolet pump–probe studies of one-femtosecond-scale electron dynamics

Generation of Attosecond Light Pulses from Gas and Solid State Media

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