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Second harmonic generation (SHG) spectroscopy in the visible and infrared regions has been a useful tool to selectively probe electronic properties at surfaces and interfaces. By examining variation of SHG under a magnetic field, one can also evaluate magnetic properties at the surfaces/interfaces. When multiple elements are involved in SHG, however, it is difficult to separate their contributions. In order to meet the demand of studying increasingly complex magnetic multilayer materials, element selectivity is desired. Here, using an Fe-based multilayer sample with broken inversion symmetry, we present observation of magnetization-induced SHG in the soft x-ray regime around the Fe M-shell absorption edge. Significant variation of SHG signal was captured depending on the direction of the magnetic moment, assuring sensitivity of the measurement likely enhanced by the Fe M-edge inner-shell resonance. The present methodology paves the way for element specific studies of magnetic properties at buried interfaces. [ABSTRACT FROM AUTHOR]

Control of the polarization of an X‐ray free‐electron laser (XFEL) has been performed using an X‐ray phase retarder (XPR) in combination with an arrival timing diagnostic on BL3 of the SPring‐8 Angstrom Compact free‐electron LAser (SACLA). To combine with the timing diagnostic, a pink beam was incident on the XPR crystal and then monochromated in the vicinity of samples. A high degree of circular polarization of ∼97% was obtained experimentally at 11.567 keV, which agreed with calculations based on the dynamical theory of X‐ray diffraction. This system enables pump–probe experiments to be operated using circular polarization with a time resolution of 40 fs to investigate ultrafast magnetic phenomena. [ABSTRACT FROM AUTHOR]

A common challenge for pump-probe studies of structural dynamics at X-ray free-electron lasers (XFELs) is the determination of time zero (T0)--the time an optical pulse (e.g., an optical laser) arrives coincidently with the probe pulse (e.g., a XFEL pulse) at the sample position. In some cases, T0 might be extracted from the structural dynamics of the sample's observed response itself, but generally, an independent robust method is required or would be superior to the inferred determination of T0. In this paper, we present how the structural dynamics in ultrafast melting of bismuth can be exploited for a quickly performed, reliable and accurate determination of T0 with a precision below 20 fs and an overall experimental accuracy of 50 fs to 150 fs (estimated). Our approach is potentially useful and applicable for fixed-target XFEL experiments, such as serial femtosecond crystallography, utilizing an optical pump pulse in the ultraviolet to near infrared spectral range and a pixelated 2D photon detector for recording crystallographic diffraction patterns in transmission geometry. In comparison to many other suitable approaches, our method is fairly independent of the pumping wavelength (UV-IR) as well as of the X-ray energy and offers a favorable signal contrast. The technique is exploitable not only for the determination of temporal characteristics of the experiment at the interaction point but also for investigating important conditions affecting experimental control such as spatial overlap and beam spot sizes. [ABSTRACT FROM AUTHOR]

We have developed a room-temperature calorimeter for absolute radiant power measurements of x-ray free-electron lasers. This room-temperature calorimeter is an electrical substitution device based on the equivalence of electrical and radiant heating. Consequently, the measured radiant powers are traceable to electrical standards, i.e., the International System Units (SI). We demonstrated the performance of the room-temperature calorimeter by electrical power measurements (offline tests). In the offline tests, the room-temperature calorimeter was proven to be able to measure external powers up to at least 6.9 mW, which exceeds the upper limit (~4 mW) of a cryogenic radiometer (the primary standard detector in Japan). In addition, measurement uncertainties of the room-temperature calorimeter were evaluated to be less than 1.0%, which is adequate for the radiant power measurements of x-ray free-electron lasers. An indirect comparison with the cryogenic radiometer was performed using a synchrotron radiation source to confirm the validity of the absolute radiant powers measured with the room-temperature calorimeter. The absolute radiant powers measured by the calorimeter agreed with those measured by the cryogenic radiometer within 0.6%, which is less than the relative standard uncertainty of the comparison (1.0%). [ABSTRACT FROM AUTHOR]

A beamline for the x-ray free electron laser (XFEL) of SPring-8 Angstrom Compact free electron LAser (SACLA) provides hard x-ray pulses in the range 4.5-19.5 keV. Its optical system in an optics hutch delivers a pink beam below 15 keV with either of two double-mirror systems or a monochromatic beam with a double-crystal monochromator. These XFEL beams are used for various types of measurement at experimental stations, e.g. x-ray diffraction, coherent diffraction imaging, x-ray spectroscopy and pump-and-probe measurement. The experimental stations consist of experimental hutches and control stations, and a femtosecond optical laser which is synchronized with XFEL pulses. Photon diagnostics have been performed for measuring radiation parameters in a shot-by-shot manner. [ABSTRACT FROM AUTHOR]

The electronic and geometric structures and photodissociation dynamics of the chromium trimer ion, Cr3 +, were investigated by photodissociation spectroscopy in the photon-energy range from 1.32 to 5.52 eV. The branching fractions of the product ions, Cr+ and Cr2 +, exhibit stepwise changes at the threshold energies for dissociation into Cr++Cr2, Cr+Cr2 +, Cr++2Cr, and Cr*+Cr2 +. It is noted that Cr2 + is produced even above the threshold for atomization; the excess energy is redistributed to produce a fragment atom, Cr*, in an excited state. The photodissociation action spectrum is well explained by a mixture of simulated spectra for two nearly-degenerate structural isomers identified by density functional calculations: those having a metastable C2v structure and the most stable structure slightly distorted from the C2v one. The barrier height between the two isomers which is lower than the zero-point energy suggests that Cr3 + has an intrinsically floppy structure. [ABSTRACT FROM AUTHOR]

A correction is presented to the article, "Fluence thresholds for grazing incidence hard x-ray mirrors" which was published in a 2019 issue of the periodical.

Advances in free electron lasers (FELs) which generate high energy photons are expected to open novel nonlinear optics in the x-ray and vacuum ultraviolet (VUV) regions. In this paper, we report a new method for performing VUV-FEL focusing experiments. A VUV-FEL was focused with Kirkpatrick-Baez optics on a multilayer target, which contains fused silica as a fluorescent material. By measuring the fluorescence, a 5.6×4.9 μm2 focal spot was observed in situ. Fluorescence was used to measure the saturable absorption of VUV pulses in the tin layer. The transmission increases nonlinearly higher with increasing laser intensity. [ABSTRACT FROM AUTHOR]

The pulse energies of a free electron laser have accurately been measured in the hard x-ray spectral range. In the photon energy regime from 4.4 keV to 16.8 keV, pulse energies up to 100 μJ were obtained at the hard x-ray laser facility SACLA (SPring-8 Ångstrom Compact free-electron LAser). Two independent methods, using a cryogenic radiometer and a gas monitor detector, were applied and agreement within 3.3% was achieved. Based on our validated pulse energy measurement, a SACLA online monitor detector could be calibrated for all future experiments. [ABSTRACT FROM AUTHOR]