Development of speckle-free channel-cut crystal optics using plasma chemical vaporization machining for coherent x-ray applications

We have developed a method of fabricating speckle-free channel-cut crystal optics with plasma chemical vaporization machining, an etching method using atmospheric-pressure plasma, for coherent X-ray applications. We investigated the etching characteristics to silicon crystals and achieved a small surface roughness of less than 1 nm rms at a removal depth of >10 μm, which satisfies the requirements for eliminating subsurface damage while suppressing diffuse scattering from rough surfaces. We applied this method for fabricating channel-cut Si(220) crystals for a hard X-ray split-and-delay optical system and confirmed that the crystals provided speckle-free reflection profiles under coherent X-ray illumination.Takashi Hirano, Taito Osaka, Yasuhisa Sano, Yuichi Inubushi, Satoshi Matsuyama, Kensuke Tono, Tetsuya Ishikawa, Makina Yabashi, and Kazuto Yamauchi, "Development of speckle-free channel-cut crystal optics using plasma chemical vaporization machining for coherent x-ray applications", Review of Scientific Instruments 87, 063118 (2016) https://doi.org/10.1063/1.4954731

Thin crystal development and applications for hard x-ray free-electron lasers

Taito Osaka, Makina Yabashi, Yasuhisa Sano, Kensuke Tono, Yuichi Inubushi, Takahiro Sato, Kanade Ogawa, Satoshi Matsuyama, Tetsuya Ishikawa, and Kazuto Yamauchi "Thin crystal development and applications for hard x-ray free-electron lasers", Proc. SPIE 8848, Advances in X-Ray/EUV Optics and Components VIII, 884804 (27 September 2013); https://doi.org/10.1117/12.2023465

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

Development of split-delay x-ray optics using Si(220) crystals at SACLA

Taito Osaka, Takashi Hirano, Makina Yabashi, Yasuhisa Sano, Kensuke Tono, Yuichi Inubushi, Takahiro Sato, Kanade Ogawa, Satoshi Matsuyama, Tetsuya Ishikawa, and Kazuto Yamauchi "Development of split-delay x-ray optics using Si(220) crystals at SACLA", Proc. SPIE 9210, X-Ray Free-Electron Lasers: Beam Diagnostics, Beamline Instrumentation, and Applications II, 921009 (8 October 2014); https://doi.org/10.1117/12.2060238

Systematic-error-free wavefront measurement using an X-ray single-grating interferometer

In this study, the systematic errors of an X-ray single-grating interferometer based on the Talbot effect were investigated in detail. Non-negligible systematic errors induced by an X-ray camera were identified and a method to eliminate the systematic error was proposed. Systematic-error-free measurements of the wavefront error produced by multilayer focusing mirrors with large numerical apertures were demonstrated at the SPring-8 Angstrom Compact free electron LAser. Consequently, wavefront aberration obtained with two different cameras was found to be consistent with an accuracy better than λ/12.Takato Inoue, Satoshi Matsuyama, Shogo Kawai, Hirokatsu Yumoto, Yuichi Inubushi, Taito Osaka, Ichiro Inoue, Takahisa Koyama, Kensuke Tono, Haruhiko Ohashi, Makina Yabashi, Tetsuya Ishikawa, and Kazuto Yamauchi, "Systematic-error-free wavefront measurement using an X-ray single-grating interferometer", Review of Scientific Instruments 89, 043106 (2018), https://doi.org/10.1063/1.5026440

Development of an experimental platform for combinative use of an XFEL and a high-power nanosecond laser

We developed an experimental platform for combinative use of an X-ray free electron laser (XFEL) and a high-power nanosecond laser. The main target of the platform is an investigation of matter under high-pressure states produced by a laser-shock compression. In this paper, we show details of the experimental platform, including XFEL parameters and the focusing optics, the laser irradiation system and X-ray diagnostics. As a demonstration of the high-power laser-pump XFEL-probe experiment, we performed an X-ray diffraction measurement. An in-situ single-shot X-ray diffraction pattern expands to a large angle side, which shows a corundum was compressed by laser irradiation.Inubushi, Y.; Yabuuchi, T.; Togashi, T.; Sueda, K.; Miyanishi, K.; Tange, Y.; Ozaki, N.; Matsuoka, T.; Kodama, R.; Osaka, T.; Matsuyama, S.; Yamauchi, K.; Yumoto, H.; Koyama, T.; Ohashi, H.; Tono, K.; Yabashi, M. Development of an Experimental Platform for Combinative Use of an XFEL and a High-Power Nanosecond Laser. Appl. Sci. 2020, 10, 2224. https://doi.org/10.3390/app10072224

Interplay of thermal and non-thermal effects in x-ray-induced ultrafast melting

X-ray laser-induced structural changes in silicon undergoing femtosecond melting have been investigated by using an x-ray pump-x-ray probe technique. The experimental results for different initial sample temperatures reveal that the onset time and the speed of the atomic disordering are independent of the initial temperature, suggesting that equilibrium atomic motion in the initial state does not play a pivotal role in the x-ray-induced ultrafast melting. By comparing the observed time-dependence of the atomic disordering and the dedicated theoretical simulations, we interpret that the energy transfer from the excited electrons to ions via electron-ion coupling (thermal effect) as well as a strong modification of the interatomic potential due to electron excitations (non-thermal effect) trigger the ultrafast atomic disordering. Our finding of the interplay of thermal and non-thermal effects in the x-ray-induced melting demonstrates that accurate modeling of intense x-ray interactions with matter is essential to ensure a correct interpretation of experiments using intense x-ray laser pulses