arXiv subjects

Ichiro Inoue

Publications and source records attributed to Ichiro Inoue.

22 records · Page 2Linked to original sources

arXiv2020

Nonlinear resonant X-ray Raman scattering

We report the observation of a novel nonlinear effect in the hard x-ray range. Upon illuminating Fe and Cu metal foils with intense x-ray pulses tuned near their respective K edges, photons at nearly twice the incoming photon energy are emitted. The signal rises quadratically with the incoming intensity, consistent with two-photon excitation. The spectrum of emitted high-energy photons comprises multiple Raman lines that disperse with the incident photon energy. Upon reaching the double K-shell ionization threshold, the signal strength undergoes a marked rise. Above this threshold, the lines cease dispersing, turning into orescence lines with energies much greater than obtainable by single electron transitions, and additional Raman lines appear. We attribute these processes to electron-correlation mediated multielectron transitions involving double-core hole excitation and various two-electron de-excitation processes to a final state involving one or more L and M core-holes.

physics.atom-ph↗

arXiv2020

Nanofocusing optics for an X-ray free-electron laser generating an extreme intensity of 100 EW/cm$^2$ using total reflection mirrors

A nanofocusing optical system referred to as $\textit{100 exa}$ for an X-ray free-electron laser (XFEL) was developed to generate an extremely high intensity of 100 EW/cm$^2$ (10$^2$$^0$ W/cm$^2$) using total reflection mirrors. The system is based on Kirkpatrick-Baez geometry, with 250 mm long elliptically figured mirrors optimized for the SPring-8 Angstrom Compact Free-Electron Laser (SACLA) XFEL facility. The nano-precision surface employed is coated with rhodium and offers a high reflectivity of 80%, with a photon energy of up to 12 keV, under total reflection conditions. Incident X-rays on the optics are reflected with a large spatial acceptance of over 900 $μ$m. The focused beam is 210 nm $\times$ 120 nm (full width at half maximum) and was evaluated at a photon energy of 10 keV. The optics developed for $\textit{100 exa}$ efficiently achieved an intensity of 1 $\times$ 10$^2$$^0$ W/cm$^2$ with a pulse duration of 7 fs and a pulse energy of 150 $μ$J (25% of the pulse energy generated at the light source). The experimental chamber, which can provide varied stage arrangements and sample conditions, including vacuum environments and atmospheric pressure helium, was set up with the focusing optics to meet the experimental requirements.

physics.app-ph↗

arXiv2018

A micro channel-cut crystal X-ray monochromator for a self-seeded hard X-ray free-electron laser

A channel-cut Si(111) crystal with a channel width of 90 $μ$m was developed for achieving reflection self-seeding in hard X-ray free-electron lasers (XFELs). With the crystal, a monochromatic seed pulse is produced from a broadband XFEL pulse generated in the first-half undulators with an optical delay of 119 fs at 10 keV. The small optical delay allows a temporal overlap between the seed optical pulse and the electron bunch by using a small magnetic chicane for the electron beam at the middle of the undulator section. A peak reflectivity reached 67%, which is a reasonable value as compared with the theoretical one of 81%. By using this monochromator, a monochromatic seed pulse without broadband background in spectrum was obtained at SACLA with a conversion efficiency from a broadband XFEL pulse of $\sim 2 \times 10^{-2}$, which is $\sim 10$ times higher than that of transmission self-seeding using a thin diamond (400) monochromator.

physics.ins-det↗

arXiv2018

Superfluorescence, free-induction decay, and four-wave mixing: propagation of free-electron laser pulses through a dense sample of helium ions

We report an experimental and numerical study of the propagation of free-electron laser pulses (wavelength 24.3 nm) through helium gas. Ionisation and excitation populates the He$^{+}$ 4$p$ state. Strong, directional emission was observed at wavelengths of 469 nm, 164 nm, 30.4 nm, and 24.5 nm. We interpret the emissions at 469 nm and 164 nm as 4$p$-3$s$-2$p$ cascade superfluorescence, that at 30.4 nm as yoked superfluorescence on the 2$p$-1$s$ transition, and that at 25.6 nm as free-induction decay of the 3$p$ state.

physics.atom-ph↗