Atomic photoionization in combined intense XUV free-electron and infrared laser fields

Radcliffe, P.; Arbeiter, Mathias; Li, W B; Düsterer, S.; Redlin, H.; Hayden, P.; Hough, P.; Richardson, Vincent; Costello, J. T.; Fennel, Thomas; Meyer, Michael

doi:10.1088/1367-2630/14/4/043008

Cited by 45 publications

(47 citation statements)

References 23 publications

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“…These lines are called 'sidebands' and are ideal candidates for a first characterization of the FEL pulses. In addition, the quasi-monochromaticity of the FELs makes it possible to observe, for high dressing fields, absorption and emission of more than one NIR photon [72,73], avoiding interference effects present in similar experiments with broader-bandwidth XUV pulses of high-harmonic-generation sources [74]. In the following we will always use the term 'X-ray' for the FEL pulses, meant to cover the whole spectral range from XUV (>10 eV) over soft X-rays (>100 eV) to hard X-rays (>5 keV), to discern them from other short-wavelength sources as e.g., high harmonic-generated XUV pulses.…”

Section: Sideband Methods For X-ray Pulse Characterizationmentioning

confidence: 99%

Ultrashort Free-Electron Laser X-ray Pulses

et al. 2017

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For the investigation of processes happening on the time scale of the motion of bound electrons, well-controlled X-ray pulses with durations in the few-femtosecond and even sub-femtosecond range are a necessary prerequisite. Novel free-electron lasers sources provide these ultrashort, high-brightness X-ray pulses, but their unique aspects open up concomitant challenges for their characterization on a suitable time scale. In this review paper we describe progress and results of recent work on ultrafast pulse characterization at soft and hard X-ray free-electron lasers. We report on different approaches to laser-assisted time-domain measurements, with specific focus on single-shot characterization of ultrashort X-ray pulses from self-amplified spontaneous emission-based and seeded free-electron lasers. The method relying on the sideband measurement of X-ray electron ionization in the presence of a dressing optical laser field is described first. When the X-ray pulse duration is shorter than half the oscillation period of the streaking field, few-femtosecond characterization becomes feasible via linear streaking spectroscopy. Finally, using terahertz fields alleviates the issue of arrival time jitter between streaking laser and X-ray pulse, but compromises the achievable temporal resolution. Possible solutions to these remaining challenges for single-shot, full time-energy characterization of X-ray free-electron laser pulses are proposed in the outlook at the end of the review.

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Section: Sideband Methods For X-ray Pulse Characterizationmentioning

confidence: 99%

Ultrashort Free-Electron Laser X-ray Pulses

et al. 2017

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“…Whereas in the former, the laser intensity is directly related, in a non-trivial way, to the intensity of the appearing sideband peaks in the PE spectrum [8,14,15], the latter has been used to characterize the shape and duration of an IR laser pulse with a technique called "streak camera" [16][17][18][19]. Furthermore, the variation of the polarization states of each field gives rise to dichroic effects in the PE spectrum, which opens the door to the control of the electronic emission [6,9,[20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Electron emission perpendicular to the polarization direction in laser-assisted XUV atomic ionization

2017

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We present a theoretical study of ionization of the hydrogen atom due to an XUV pulse in the presence of an IR laser with both fields linearly polarized in the same direction. In particular, we study the energy distribution of photoelectrons emitted perpendicularly to the polarization direction. By means of a very simple semiclassical model which considers electron trajectories born at different ionization times, the electron energy spectrum can be interpreted as the interplay of intraand intercycle interferences. The intracycle interference pattern stems from the coherent superposition of four electron trajectories giving rise to (i) interference of electron trajectories born during the same half cycle (intrahalfcycle interference) and (ii) interference between electron trajectories born during the first half cycle with those born during the second half cycle (interhalfcycle interference). The intercycle interference is responsible for the formation of the sidebands. We also show that the destructive interhalfcycle interference for the absorption and emission of an even number of IR laser photons is responsible for the characteristic sidebands in the perpendicular direction separated by twice the IR photon energy. We analyze the dependence of the energy spectrum on the laser intensity and the time delay between the XUV pulse and the IR laser. Finally, we show that our semiclassical simulations are in very good agreement with quantum calculations within the strong field approximation and the numerical solution of the time-dependent Schrödinger equation.

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“…Although quite strong, moreover, we suppose some NIR laser pulse with many optical cycles so that it can be described as a monochromatic plane-wave. Together, these two assumptions ensure that the 'sideband regime' holds [15], in which photoelectrons are expected not only at the given photoline but also at energies that differ by one or several energy quanta of the the NIR field. Moreover, both fields are supposed to propagate along a common beam axis that is taken also as the quantization axis (z-axis).…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…For two plane waves, as shown in Sect. II C 2 a, the two-color ATI amplitude (15) and, hence, the corresponding photoionization probability only depends on the product of the two spin angular momentum (SAM) projections, i.e. the helicities of the XUV and laser photons.…”

Section: Circular Dichroism For Plane-wavesmentioning

confidence: 99%

“…In two-color ATI, such a XUV field is often combined with intense NIR laser pulses in order to investigate the ionization of * d.seipt@gsi.de sub-valence electrons: While, under these circumstances, the NIR field alone is not sufficient to ionize the atoms or molecules efficiently, it is intense enough to stimulate the absorption or emission of one or several additional NIR photons by the outgoing electron. This non-perturbative interaction of the electrons with both, the XUV and NIR fields then leads to the well-known 'sidebands' that typically occur as satellites to the normal photolines [14,15]. Such sidebands were first observed in the two-color ATI of noble gases as well as in laser-assisted Auger processes [16][17][18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

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Probing the energy flow in Bessel light beams using atomic photoionization

2016

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The two-color above-threshold ionization (ATI) of atoms and ions is investigated for a vortex Bessel beam in the presence of a strong near-infrared (NIR) light field. While the photoionization is caused by the photons from the weak but extreme ultra-violet (XUV) vortex Bessel beam, the energy and angular distribution of the photoelectrons and their sideband structure are affected by the planewave NIR field. We here explore the energy spectra and angular emission of the photoelectrons in such two-color fields as a function of the size and location of the target atoms with regard to the beam axis. In addition, analogue to the circular dichroism in typical two-color ATI experiments with circularly polarized light, we define and discuss seven different dichroism signals for such vortex Bessel beams that arise from the various combinations of the orbital and spin angular momenta of the two light fields. For localized targets, it is found that these dichroism signals strongly depend on the size and position of the atoms relative to the beam. For macroscopically extended targets, in contrast, three of these dichroism signals tend to zero, while the other four just coincide with the standard circular dichroism, similar as for Bessel beams with small opening angle. Detailed computations of the dichroism are performed and discussed for the 4s valence-shell photoionization of Ca + ions.

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Atomic photoionization in combined intense XUV free-electron and infrared laser fields

Cited by 45 publications

References 23 publications

Ultrashort Free-Electron Laser X-ray Pulses

Ultrashort Free-Electron Laser X-ray Pulses

Electron emission perpendicular to the polarization direction in laser-assisted XUV atomic ionization

Probing the energy flow in Bessel light beams using atomic photoionization

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