Anomalous nonlinear X-ray Compton scattering

Fuchs, M.; Trigo, M.; Chen, Jian; Ghimire, Shambhu; Shwartz, Sharon; Kozina, Michael; Jiang, Mason; Henighan, Thomas; Bray, C. C.; Ndabashimiye, Georges; Bucksbaum, P. H.; Feng, Yiping; Herrmann, Sven; Carini, G.; Pines, J.; Hart, Philip; Kenney, C.; Guillet, Serge; Boutet, Sébastien; Williams, Garth J.; Messerschmidt, Marc; Seibert, M.; Moeller, Stefan; Hastings, J. B.; Reis, David A.

doi:10.1038/nphys3452

Cited by 119 publications

(108 citation statements)

References 33 publications

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“…threshold, peak (2) is weaker and is ∼1/3 of the signal above threshold. The presence of nonlinear background could be due to two-photon Compton scattering (TPC), such as seen recently in Be by Fuchs et al [7]. In the case of Zr, this would correspond the simultaneous scattering of two photons from an electron outside the K shell producing a single photon redshifted from twice the photon energy.…”

Section: Methodsmentioning

confidence: 99%

“…Below threshold we measure a nonlinear contribution to the signal that is possibly due to nonresonant two-photon Compton scattering. More detailed measurements of the angular distribution and spectrum would allow us to further separate the TPA and TPC processes, as the former produces K florescence, which is narrow and emitted into 4π , and the latter a broad spectrum emitted in a nondipolar angular distribution [7].…”

Section: Discussion and Outlookmentioning

confidence: 99%

“…Thus multiphoton interactions scale with the frequency as ω −2n+1 , and only with the advent of x-ray free-electron lasers (XFEL) [5,6] have nonsequential two-photon interactions become possible at hard x-ray energies. This includes two-photon Compton scattering by Fuchs et al [7], x-ray second-harmonic generation by Shwartz et al [8], and two-photon absorption by Tamasaku et al [9]. Two-photon absorption (TPA) was first considered theoretically by Göppert-Mayer [10].…”

Section: Introductionmentioning

confidence: 99%

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Nonsequential two-photon absorption from the K shell in solid zirconium

et al. 2016

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We report the observation of nonsequential two-photon absorption from the K shell of solid Zr (atomic number Z = 40) using intense x-ray pulses from the Spring-8 Angstrom Compact Free-Electron Laser (SACLA). We determine the generalized nonlinear two-photon absorption cross section at the two-photon threshold in the range of 3.9-57 ×10 −60 cm 4 s bounded by the estimated uncertainty in the absolute intensity. The lower limit is consistent with the prediction of 3.1 ×10 −60 cm 4 s from the nonresonant Z −6 scaling for hydrogenic ions in the nonrelativistic, dipole limit.

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Section: Methodsmentioning

confidence: 99%

Section: Discussion and Outlookmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nonsequential two-photon absorption from the K shell in solid zirconium

et al. 2016

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“…The brightness of XFELs is many orders of magnitude higher than that of synchrotron sources [12]. Unprecedentedly ultraintense x-ray pulses enable us to study nonlinear x-ray physics [13,14,15,16], including nonlinear two-photon x-ray Compton scattering [17,18]. The features of ultraintense and ultrashort XFEL pulses are useful to create warm dense matter [19], and the inelastic x-ray scattering technique has been developed to measure characteristics (density and temperature) of high energy density plasma [20,21,22,23].…”

Section: Introductionmentioning

confidence: 99%

Compton spectra of atoms at high x-ray intensity

Son

Geffert

Santra

2017

J. Phys. B: At. Mol. Opt. Phys.

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Abstract. Compton scattering is the nonresonant inelastic scattering of an xray photon by an electron and has been used to probe the electron momentum distribution in gas-phase and condensed-matter samples. In the low x-ray intensity regime, Compton scattering from atoms dominantly comes from bound electrons in neutral atoms, neglecting contributions from bound electrons in ions and free (ionized) electrons. In contrast, in the high x-ray intensity regime, the sample experiences severe ionization via x-ray multiphoton multiple ionization dynamics. Thus, it becomes necessary to take into account all the contributions to the Compton scattering signal when atoms are exposed to high-intensity x-ray pulses provided by x-ray free-electron lasers (XFELs). In this paper, we investigate the Compton spectra of atoms at high xray intensity, using an extension of the integrated x-ray atomic physics toolkit, xatom.As the x-ray fluence increases, there is a significant contribution from ionized electrons to the Compton spectra, which gives rise to strong deviations from the Compton spectra of neutral atoms. The present study provides not only understanding of the fundamental XFEL-matter interaction but also crucial information for single-particle imaging experiments, where Compton scattering is no longer negligible.

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“…Prior to the development of free electron lasers (FELs), only parametric downconversion had been observed [17]. While the advent of XFELs has recently enabled second-and third-order nonlinear spectroscopies at hard x-ray energies, including SHG [2], SFG [1], two-photon absorption [4], and inelastic Compton scattering [18], current hard x-ray FELs lack the longitudinal and temporal coherence necessary for efficiently satisfying the phase-matching conditions required for nonlinear spectroscopies, thus, making the exploitation of some of these techniques difficult [19,20]. Furthermore, the shorter hard x-ray wavelengths (λ < 0.2 nm) induce second harmonic and sum frequency generation even within centrosymmetric media, as the observed response depends on material inhomogeneity on the length scale of the x-ray wavelength, similar to how SHG is seen in a plasma, and effectively making this method a bulk probe [21].…”

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confidence: 99%

X-Ray Probe Targets Interfaces

Nilsson

2018

Physics

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Nonlinear optical processes at soft x-ray wavelengths have remained largely unexplored due to the lack of available light sources with the requisite intensity and coherence. Here we report the observation of soft x-ray second harmonic generation near the carbon K edge (∼284 eV) in graphite thin films generated by high intensity, coherent soft x-ray pulses at the FERMI free electron laser. Our experimental results and accompanying first-principles theoretical analysis highlight the effect of resonant enhancement above the carbon K edge and show the technique to be interfacially sensitive in a centrosymmetric sample with second harmonic intensity arising primarily from the first atomic layer at the open surface. This technique and the associated theoretical framework demonstrate the ability to selectively probe interfaces, including those that are buried, with elemental specificity, providing a new tool for a range of scientific problems. DOI: 10.1103/PhysRevLett.120.023901 Nonlinear optics has recently been extended from visible and near UV wavelengths to new regimes with the development of x-ray free electron lasers (XFELs) capable of delivering x-ray pulses with high brightness, ultrashort pulse duration, and high coherence [1][2][3][4][5][6][7]. One fundamental nonlinear probe is second harmonic generation (SHG), a secondorder process which combines two photons of the same energy to generate a single photon with twice the energy [8]. At infrared, visible, and ultraviolet wavelengths, secondorder nonlinear spectroscopies have become important tools in surface science, as symmetry considerations within the dipole approximation constrain signal generation to regions lacking centrosymmetry, such as surfaces and interfaces [9][10][11][12]. In contrast, at hard x-ray wavelengths, second harmonic and sum frequency generation (SFG) have been observed in centrosymmetric materials with a nonuniform electron density and are essentially bulk probes [1,2]. As soft x-ray wavelengths fall in between the hard x-ray and UV regimes, there has been uncertainty regarding the interface specificity of soft x-ray SHG. Here, by utilizing a recently constructed, highly coherent, soft x-ray free electron laser [13,14], we report the first observation of soft x-ray second harmonic generation near the carbon K edge (∼284 eV). Our experimental results and accompanying theoretical analysis indicate that soft x-ray SHG is an interface-specific probe with symmetry constraints similar to optical SHG or SFG, and is highly sensitive to resonance effects. This enables a powerful new approach for surface and interface analysis with broad applicability to many scientific fields, as it combines the elemental and chemical specificity of x-ray absorption spectroscopy with the rigorous interfacial specificity of second-order nonlinear spectroscopies, while maintaining a fully coherent signal. With several new coherent free electron lasers under development (SwissFEL, SXFEL, LCLS-II, FLASH2020) [15,16], this new technique offers exciting application...

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Anomalous nonlinear X-ray Compton scattering

Cited by 119 publications

References 33 publications

Nonsequential two-photon absorption from the K shell in solid zirconium

Nonsequential two-photon absorption from the K shell in solid zirconium

Compton spectra of atoms at high x-ray intensity

X-Ray Probe Targets Interfaces

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