We present the development of a phase compensator for wavefront control of X-rays. The optical device is a 150 mm-long
total reflection mirror, the shape of which can be curved by adjusting the bias voltages of 36 piezoelectric ceramic
plates attached to the mirror. The mirror surface was smoothed and made flat by elastic emission machining. To achieve
a high degree of the accuracy in the controllability of a curved line, a Fizeau interferometer is placed in front of the
mirror surface to monitor its shape in the experiment. We will apply this device to the optical system for the realization
of sub-10-nm hard X-ray focusing.
Aberration effects in curved multilayers for hard X rays are studied using a simple analytical approach. The method is based on geometrical ray tracing including refraction effects up to the first order of the refractive index decrement δ. The interpretation of the underlying equations provides fundamental insight into the focusing properties of these devices. Using realistic values for the multilayer parameters the impact on spot broadening and chromaticity is evaluated. The work is complemented by a comparison with experimental focusing results obtained with a W/B4C multilayer mirror.
Extremely high surface figure accuracy is required for hard x-ray nanofocusing mirrors to realize an ideal spherical
wavefront in a reflected x-ray beam. We performed the figure correction of an elliptically figured mirror by a differential
deposition technique on the basis of the wavefront phase error, which was calculated by a phase-retrieval method using
only intensity profile on the focal plane. The measurements of the intensity profiles were performed at the 1-km-long
beamline at SPring-8. The two measurements before and after the figure correction indicate that the beamwaist structure
around the focal point is greatly improved.
Nanofocused X-rays are indispensable because they can provide high spatial resolution and high sensitivity for X-ray
nanoscopy/spectroscopy. A focusing system with reflective optics is one of the most promising methods for producing
nanofocused X-rays due to its high efficiency and beams size. So, far we realize efficient hard X-ray focusing with a
beam size of 25nm. Our next project is realization of sub-10nm hard X-ray focusing. Here, we describe the design of
the graded multilayer mirror and evaluation method for hard X-ray focused beam.
Focusing methods using mirror optics are intensively studied in the field of X-ray microscopy because mirror optics has useful features such as high photon efficiency and no chromatic aberrations. Employing a wave-optical method, we investigated the relationship between the nature of figure errors on the mirror surface and optics performances. We also evaluated glancing angle sensitivity to focused beam and beamwaist stuructures. Obtained results showed unprecedented degrees of surface figure accuracy such as higher than 4 nm was required to realize nearly diffraction limited nanobeam. This simulation can also give important information for align KB mirrors setup.
We developed a high-spatial-resolution scanning X-ray fluorescence microscope (SXFM) with Kirkpatrick-Baez
mirrors. As a result of focusing tests at 15 keV, the focused beam having a FWHM of 30 x 50 nm2 was achieved.
Additionally, the size was controllable within the wide range of 30 ~ 1400 nm merely by adjusting the X-ray source
size. The observation of a fine test chart suggests that SXFM enables us to visualize the element distribution inside the
pattern at a spatial resolution better than 30 nm. We applied the SXFM to observe intracellular elemental distributions
at a single-cell level, so that we could acquire element distribution maps with a spatial resolution of sub-100 nm and
lower detection limit of 0.01 fg.
We realized nearly diffraction-limited performance with a FWHM focal spot size of 25 nm at an x-ray energy of 15 keV at SPring-8. We explain performances of fabricated x-ray mirror, its fabrication technologies and future plan for realizing sub-10-nm focusing. We developed a novel method of at-wavelength metrology for evaluating the focusing hard x-ray beam in a grazing-incidence optical system. The metrology is based on the numerical retrieval method using the intensity distribution 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 by the optical interferometer and confirmed to be in good agreement with it. This technique has potential for characterizing wave-front aberration on elliptical mirrors for the sub-10-nm focusing.
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