Explaining the x-ray nonlinear susceptibility of diamond and silicon near absorption edges

International audienceWe report the observation and the theoretical explanation of the parametric down-conversion nonlinear susceptibility at the K-absorption edge of diamond and at the L 23-absorption edge of a silicon crystal. Using arguments similar to those invoked to successfully predict resonant inelastic x-ray spectra, we derive an expression for the renormalization term of the nonlinear susceptibility at the x-ray edges, which can be evaluated by using first-principles calculations of the atomic scattering factor f 1. Our model is shown to reproduce the observed enhancement of the parametric down-conversion at the diamond K and the Si L 23 edges rather than the suppression previously claimed

Hard X-ray nanofocusing using adaptive focusing optics based on piezoelectric deformable mirrors

An adaptive Kirkpatrick-Baez mirror focusing optics based on piezoelectric deformable mirrors was constructed at SPring-8 and its focusing performance characteristics were demonstrated. By adjusting the voltages applied to the deformable mirrors, the shape errors (compared to a target elliptical shape) were finely corrected on the basis of the mirror shape determined using the pencil-beam method, which is a type of at-wavelength figure metrology in the X-ray region. The mirror shapes were controlled with a peak-to-valley height accuracy of 2.5 nm. A focused beam with an intensity profile having a full width at half maximum of 110 × 65 nm (V × H) was achieved at an X-ray energy of 10 keV.Takumi Goto, Hiroki Nakamori, Takashi Kimura, Yasuhisa Sano, Yoshiki Kohmura, Kenji Tamasaku, Makina Yabashi, Tetsuya Ishikawa, Kazuto Yamauchi, and Satoshi Matsuyama, "Hard X-ray nanofocusing using adaptive focusing optics based on piezoelectric deformable mirrors", Review of Scientific Instruments 86, 043102 (2015) https://doi.org/10.1063/1.4916617

Hard x-ray intensity autocorrelation using direct two-photon absorption

An intensity autocorrelation measurement is demonstrated to characterize a pulse duration of 9-keV x-ray free-electron laser (XFEL) pulses from a split-delay optical (SDO) system with four-bounce silicon 220 reflections in each branch. XFEL pulse replicas with variable time delays are generated by the SDO system itself. High intensity of >2×1016W/cm2 achieved in a self-seeding operation and careful data analysis allow the measurement with direct two-photon absorption. The autocorrelation trace gave a duration of 7.6±0.8fs in full width at half maximum for a Gaussian assumption. Furthermore, the trace shows good agreement with a simulation of the XFEL pulse shape propagating through the SDO system, irrespective of spectral chirps in the original XFEL pulses. Our results open the door toward direct temporal characterization of narrowband XFELs at the hard x-ray regime, such as self-seeded and future cavity-based XFELs, and indicate a solid way for temporal tailoring of ultrafast x-ray pulses with perfect crystals.Osaka T., Inoue I., Yamada J., et al. Hard x-ray intensity autocorrelation using direct two-photon absorption. Physical Review Research, 4, 1, L012035. https://doi.org/10.1103/PhysRevResearch.4.L012035

At-wavelength figure metrology of hard x-ray focusing mirrors

We have developed an at-wavelength wave-front metrology of a grazing-incidence focusing optical systems in the hard x-ray region. The metrology is based on numerical retrieval from the intensity profile around the focal point. We demonstrated the at-wavelength metrology and estimated the surface figure error on a test mirror. An experiment for measuring the focusing intensity profile was performed at the 1-km-long beamline (BL29XUL) of SPring-8. The obtained results were compared with the profile measured using an optical interferometer and were confirmed to be in good agreement with it. This technique is a potential method of characterizing wave-front aberrations on elliptical mirrors for sub-10-nm focusing. © 2006 American Institute of Physics.Yumoto H., Mimura H., Matsuyama S., et al. At-wavelength figure metrology of hard x-ray focusing mirrors. Review of Scientific Instruments, 77, 6, 063712 (2006) https://doi.org/10.1063/1.221687