Nonlinear Spectroscopy with X-Ray Two-Photon Absorption in Metallic Copper

Tamasaku, Kenji; Shigemasa, E.; Inubushi, Yuichi; Inoue, Ituro; Osaka, Taito; Katayama, Tetsuo; Yabashi, Makina; Koide, Akihiro; Yokoyama, Toshihiko; Ishikawa, Tetsuya

doi:10.1103/physrevlett.121.083901

Cited by 47 publications

(55 citation statements)

References 41 publications

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“…However, the observation of coherent emission at harmonics in the range from 84 to 101 indicates the possibility to extend the lasing to wavelengths as short as 2 nm (620 eV) or less in a more optimized setup, either by using EEHG directly, or with a cascade employing both EEHG and HGHG schemes 24 . Such a layout has the potential to set the stage for entirely new experiments using X-ray nonlinear optical techniques [37][38][39][40][41] .…”

Section: Discussionmentioning

confidence: 99%

Coherent soft X-ray pulses from an echo-enabled harmonic generation free-electron laser

et al. 2019

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X-ray free electron lasers (FELs), which amplify light emitted by a relativistic electron beam, are extending nonlinear optical techniques to shorter wavelengths, adding element specificity by exciting and probing electronic transitions from core levels. These techniques would benefit tremendously from having a stable FEL source, generating spectrally pure and wavelength-tunable pulses. We show that such requirements can be met by operating the FEL in the so-called echo-enabled harmonic generation (EEHG) configuration. Here, two external conventional lasers are used to precisely tailor the longitudinal phase space of the electron beam before emission of X-rays. We demonstrate high-gain EEHG lasing producing stable, intense, nearly fully coherent pulses at wavelengths as short as 5.9 nm (~211 eV) at the FERMI FEL user facility. Low sensitivity to electron-beam imperfections and observation of stable, narrow-band, coherent emission down to 2.6 nm (~474 eV) make the technique a prime candidate for generating laser-like pulses in the X-ray spectral region, opening the door to multidimensional coherent spectroscopies at short wavelengths.

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Section: Discussionmentioning

confidence: 99%

Coherent soft X-ray pulses from an echo-enabled harmonic generation free-electron laser

et al. 2019

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“…As shown, the TPA excitation probability is driven by the probability of the first absorption event. In contrast to off-resonant excitation conditions, in the two-photon process, the maximum photon energy detuning is determined by half of the absorption edge energy, 3854.5 eV for cobalt, and we estimate a TPA cross-section value at this energy to be ∼1.1 × 10 −57 cm 4 s. This estimation does not include eventual resonant effects for the second absorption event in the sequential process [31].…”

Section: Data Analysis Proceduresmentioning

confidence: 81%

“…Based on the derived cross sections for Co and available experimental and theoretical literature data [4,7,9,[31][32][33][34][35] we evaluated the dependence of the TPA cross section as a function of the atomic number. The result is presented in Fig.…”

Section: Data Analysis Proceduresmentioning

confidence: 99%

Cross-section determination for one- and two-photon absorption of cobalt at hard-x-ray energies

et al. 2019

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For incident x-ray energies below the core level ionization threshold, one-photon absorption (OPA) leads to off-resonant x-ray excitations that are mediated by a virtual intermediate electronic state. In the linear regime of x-ray interaction, this intermediate state may decay radiatively and the maximum energy of the emitted photon is given by the initial and final atomic state as well as the energy of the incident photon. In the nonlinear excitation regime, however, this intermediate state may be depleted by a second x-ray absorption process as described in the sequential two-photon absorption (TPA) mechanism. Since the same intermediate state is involved in the OPA and TPA processes, the cross-section values for OPA and TPA are interconnected. We report on the determination of cross-section values for off-resonant excitation conditions, and show how the data can be used for estimating the TPA cross section in the sequential absorption mechanism. The determined off-resonant cross sections for cobalt exhibit a Lorentz-like energy-dependent behavior allowing for an energy-dependent description of the OPA and TPA cross sections with semiempirical models. The dependence of TPA cross sections on atomic number is discussed and different scaling laws are investigated. The effect of the lifetimes of a virtual intermediate state is also studied in relation to the incidence x-ray energy.

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“…Nowadays, it is also possible to probe these systems in nonlinear regime with free-electron lasers 3,4 . That is why, in the last decade, much of experimental efforts [5][6][7][8][9][10][11][12][13][14][15] have been paid to studying the fundamental properties of nonlinear light-matter interaction, and finding use in applied fields such as nonlinear spectroscopy. The theoretical developments were in many respects following the experimental trail.…”

Section: Introductionmentioning

confidence: 99%

Breakdown of the electric dipole approximation at Cooper minima in direct two-photon ionisation

Hofbrucker¹,

Volotka²,

Fritzsche³

2020

Sci Rep

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We predict breakdown of the electric dipole approximation at nonlinear Cooper minimum in direct two-photon K−shell atomic ionisation by circularly polarised light. According to predictions based on the electric dipole approximation, we expect that tuning the incident photon energy to the Cooper minimum in two-photon ionisation results in pure depletion of one spin projection of the initially bound 1s electrons, and hence, leaves the ionised atom in a fully oriented state. We show that by inclusion of electric quadrupole interaction, dramatic drop of orientation purity is obtained. The low degree of the remaining ion orientation provides a direct access to contributions of the electron-photon interaction beyond the electric dipole approximation in the two-photon ionisation of atoms and molecules. The orientation of the photoions can be experimentally detected either directly by a Stern-Gerlach analyzer, or by means of subsequent Kα fluorescence emission, which has the information about the ion orientation imprinted in the polarisation of the emitted photons. 2/113/11

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Nonlinear Spectroscopy with X-Ray Two-Photon Absorption in Metallic Copper

Cited by 47 publications

References 41 publications

Coherent soft X-ray pulses from an echo-enabled harmonic generation free-electron laser

Coherent soft X-ray pulses from an echo-enabled harmonic generation free-electron laser

Cross-section determination for one- and two-photon absorption of cobalt at hard-x-ray energies

Breakdown of the electric dipole approximation at Cooper minima in direct two-photon ionisation

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