Hikaru Yokoyama

Wavefront measurement for a hard-X-ray nanobeam using single-grating interferometry

Wavefront measurement for a hard-X-ray nanobeam using single-grating interferometry based on the Talbot effect and the Fourier transform method was demonstrated in the 1-km-long beamline of SPring-8. 10 keV X-rays were one-dimensionally focused down to 32 nm using a total-reflection elliptical mirror. An intentionally distorted wavefront was generated using a deformable mirror placed just upstream of the focusing mirror. The wavefront measured by interferometry was cross-checked with the phase retrieval method using intensity profiles around the beam waist. Comparison of the obtained wavefront errors revealed that they are in good agreement with each other and with the wavefront error estimated from the shape of the deformable mirror at a ~0.5 rad level.

Wavefield characterization of nearly diffraction-limited focused hard x-ray beam with size less than 10 nm.

In situ wavefront compensation is a promising method to realize a focus size of only a few nanometers for x-ray beams. However, precise compensation requires evaluation of the wavefront with an accuracy much shorter than the wavelength. Here, we characterized a one-dimensionally focused beam with a width of 7 nm at 20 keV using a multilayer mirror. We demonstrate that the wavefront can be determined precisely from multiple intensity profiles measured around the beamwaist. We compare the phase profiles recovered from intensity profiles measured under the same mirror condition but with three different aperture sizes and find that the accuracy of phase retrieval is as small as λ∕12.

Development of an Adaptive Optical System for Sub‐10‐nm Focusing of Synchrotron Radiation Hard X‐rays

In the hard x‐ray region, to obtain the theoretical resolution or diffraction‐limited focusing size in an imaging optical system, both ultraprecise optics and highly accurate alignment are necessary. An adaptive optical system is used for the compensation of aberrations in various optical systems, such as optical microscopes and space telescopes. In situ wavefront control of hard x‐rays is also effective for realizing ideal performance. The aim of this paper is to develop an adaptive optical system for sub‐10‐nm hard x‐ray focusing. The adaptive optical system performs the wavefront measurement using a phase retrieval algorithm and wavefront control using grazing‐incidence deformable mirrors. Several results of experiments using the developed system are reported.

An adaptive optical system for sub-10nm hard x-ray focusing

In the hard X-ray region, to obtain the theoretical resolution or diffraction limited focusing size in an imaging optical system, both ultraprecise optics and highly accurate alignment are necessary. An adaptive optical system is used for the compensation of aberrations in various optical systems, such as optical microscopes and space telescopes. In situ wavefront control of hard X-rays is also effective for realizing ideal performance. The aim of this paper is to develop an adaptive optical system for sub-10nm hard X-ray focusing. The adaptive optical system performs the wavefront measurement using a phase retrieval algorithm and wavefront control using grazing incidence deformable mirrors. Several results of experiments using the developed system are reported.

Supernova real-time monitor system in Kamiokande

Abstract A data-analysis program to discover possible supernova neutrino bursts has been installed in the online data-acquisition computer of the Kamiokande experiment. The program automatically analyzes data within 20 min and gives an alarm to collaborators if a possible supernova neutrino burst is found. The detection efficiency of the program is 96% for a typical supernova located 50 kpc from Earth. After a careful analysis by the Kamiokande collaborators, it will be possible to inform all optical observatories in the world about the occurrence of a supernova within 3 h from the time of first detecting the neutrino burst. Information concerning the celestial position of a supernova will also be available for supernovae having a distance less than ∼ 10 kpc. This information will be helpful for observing the first optical emissions from the newly born supernova.

Micro-focusing of hard x-ray free electron laser radiation using Kirkpatrick-Baez mirror system

We developed micro-focusing Kirkpatrick-Baez (K-B) mirror optics for the X-ray free electron laser (XFEL) at the SPring-8 Angstrom Compact free electron Laser (SACLA) facility in Japan. The K-B focusing mirrors have a spatial acceptance of 600 × 600 μm2 and ultra-precision surfaces. A manipulator for precise alignment of the mirrors was also developed. The focusing properties for 10-keV X-rays were evaluated with a wire-scanning method. The focal beam size was determined to be 0.95 μm × 1.20 μm at the full width at half maximum. An increased power density of 1018 W/cm2 was achieved at the focal point. These properties were confirmed to be in good agreement with the designed value.