The EIS beamline at the seeded free-electron laser FERMI

Simoncig, Alberto; Mincigrucci, Riccardo; Principi, Emiliano; Bencivenga, Filippo; Calvi, Andrea; Foglia, Laura; Kurdi, G.; Raimondi, Lorenzo; Manfredda, Michele; Mahne, Nicola; Gobessi, R.; Gerusina, Simone; Fava, C.; Zangrando, Marco; Matruglio, Alessia; Zilio, Simone Dal; Masciotti, Valentina; Masciovecchio, C.

doi:10.1117/12.2268152

Cited by 3 publications

(3 citation statements)

References 23 publications

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“…Soft X-ray transmission experiments were performed at EIS-TIMEX at the FERMI FEL-2 free electron laser in Trieste [24][25][26][27]. FEL-2 is based on a double high gain harmonic generation (HGHG) conversion scheme wherein the first stage of the FEL serves as a pump for the second stage.…”

Section: A Experimental Designmentioning

confidence: 99%

Two-photon absorption of soft X-ray free electron laser radiation by graphite near the carbon K-absorption edge

Lam

Raj

Pascal

et al. 2018

Chemical Physics Letters

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We have examined the transmission of soft X-ray pulses from the FERMI free electron laser through carbon films of varying thickness, quantifying nonlinear effects of pulses above and below the carbon Kedge. At typical of soft X-ray free electron laser intensities, pulses exhibit linear absorption at photon energies above and below the K-edge, ~308 and ~260 eV, respectively; whereas two-photon absorption becomes significant slightly below the K-edge, ~284.2 eV. The measured two-photon absorption cross section at 284.18 eV (~6 x 10-48 cm 4 s) is 7 orders of magnitude above what is expected from a simple theory based on hydrogen-like atomsa result of resonance effects.

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Section: A Experimental Designmentioning

confidence: 99%

Two-photon absorption of soft X-ray free electron laser radiation by graphite near the carbon K-absorption edge

Lam

Raj

Pascal

et al. 2018

Chemical Physics Letters

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“…The experiments were conducted at the EIS-TIMEX endstation [22,23]. An experimental schematic is shown in Fig.…”

mentioning

confidence: 99%

Soft X-Ray Second Harmonic Generation as an Interfacial Probe

Lam¹,

Raj²,

Pascal³

et al. 2018

Phys. Rev. Lett.

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“…The experiments were conducted at the EIS-TIMEX end station [22,23]. An experimental schematic is shown in Fig.…”

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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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The EIS beamline at the seeded free-electron laser FERMI

Cited by 3 publications

References 23 publications

Two-photon absorption of soft X-ray free electron laser radiation by graphite near the carbon K-absorption edge

Two-photon absorption of soft X-ray free electron laser radiation by graphite near the carbon K-absorption edge

Soft X-Ray Second Harmonic Generation as an Interfacial Probe

X-Ray Probe Targets Interfaces

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