Masahiko Ishino

New evaluation beamline for soft x-ray optical elements

An evaluation system capable of measuring the wavelength and angular characteristics of the absolute reflectivity (or diffraction efficiency) of soft x-ray optical elements has been designed and constructed. The system was installed on a beamline (BL-11) of the AURORA, a superconducting compact storage ring, at the Synchrotron Radiation Center, Ritsumeikan University. To cover a wavelength range of 0.5 nm<λ<25 nm, this system incorporates two types of Monk–Gillieson monochromators. One is a conventional type equipped with three varied-line-spacing gratings, allowing a choice of two included angles. The other is a new type that employs a scanning mechanism based on surface normal rotation. The outline of the system and some preliminary experimental data obtained in the course of test runs are described.

Performance of a reflection-type polarizer by use of muscovite mica crystal in the soft x-ray region of 1keV

To develop the polarizer functioning in the soft x-ray region of 1keV, the polarization performance of muscovite mica has been investigated theoretically with a simulation code based on dynamical theory. As the result of calculation, muscovite mica is found to be a promising candidate as a reflection-type polarizer with the reflectivity for s polarization of 0.03 at approximately 0.9keV at the angle of incidence of 45°. In order to verify the polarization performance of muscovite mica experimentally, a symmetric Bragg reflection measurement of muscovite mica(002) was carried out using a linearly polarized undulator radiation. As a result, the maximum reflectivity for s polarization and the extinction ratio of muscovite mica were approximately 0.018 and 200 at 878eV, respectively. This result indicates that muscovite mica works as a practical polarizer in the soft x-ray region.

Boundary Structure of Mo/Si Multilayers for Soft X-Ray Mirrors

Characterizations of Mo/Si multilayers for soft X-ray mirrors have been carried out by high-resolution transmission electron microscopy (TEM) and X-ray scatterings. The crystallite size of oriented Mo in the direction normal to the (110) plane has been found to be approximately equal to the designed thickness of the Mo layer below 8 nm. However, when the Mo layer thickness becomes greater than 8 nm, the crystallite size deviates from the designed thickness and saturates at about 10 nm. The Si layer thickness is smaller than the expected one, which is calculated from the periodic length and the Mo layer thickness, indicating that the mixed layer at the interface is formed in the Si layer. The thickness and density of the mixed layer at the Mo-on-Si interface are larger than those at the Si-on-Mo interface. The sum of the thicknesses of the mixed layer is about 1.4 nm, irrespective of the Mo/Si composition. Moreover, the density of the mixed layer at the Mo-on-Si interface becomes larger with the increase of the Mo content.

New type of Monk-Gillieson monochromator capable of covering a 0.7- to 25-nm range

A new type of monochromators that incorporates two kinds of Monk-Gillieson monochromators has been designed and constructed for the purpose of realizing an evaluation beamline for characterizing soft X-ray optical elements in a wide wavelength range of 0.7-25 nm. One of the monochromators is a conventional type equipped with three varied-line-spacing plane gratings, allowing a choice of two inclusion angles. The other is a new type that employs a scanning mechanism based on Surface Normal Rotation (SNR). The SNR scheme provides high throughput at short wavelengths and simple scanning mechanism by means of a grating rotation about its normal. The monochromators is operated in the SNR and conventional modes over the ranges of 0.7-2.0 nm and 2.0-25 nm, respectively. The system was installed on a beamline of the AURORA, a superconducting compact storage ring, at the Synchrotron Radiation Center, Ritsumeikan University. In this paper we describe the optical and mechanical designs of the monochromators, and a practical method of wavelength calibration. Also experimental data are shown which demonstrate the performance and versatility of the new type of Monk-Gillieson monochromators.

Demonstration of a fully spatial coherent X-ray laser at 13.9 nm

We have recently reported the successful development of a fully coherent X-ray laser (XRL) at 13.9 nm by an oscillator-amplifier configuration with two targets. In the experiment, a seed XRL beam from the first target is injected into a plasma amplifier at the second target. The observed XRL beam has full spatial coherence and 0.2 mrad of nearly diffraction-limited divergence. In order to improve the output fluence, the amplification properties of the XRL beam have been investigated using various plasma lengths of the second amplifier target. The output energy has been improved by a factor of ten, increasing the length of the gain region to 10 mm, resulting in about 0.2 /spl mu/J of output energy.

Development of single shot soft x-ray contact microscopy system for nano-scale dynamics measurement of living biological specimen

We have been developing a picosecond single shot soft x-ray contact microscopy system for observing the nanometer-scale inner structure of the living biological specimen in a hydrated condition. The microscopy system consists of an intense IR pump laser system for generating laser-induced plasma as a soft x-ray source and x-ray microscope chamber. The pump laser system employs OPCPA (Optical Parametric Chirped Pulse Amplification) technique to obtain a high contrast pump laser pulse, and we can generate water-window x-rays effectively by combining it to an ultra-thin metal target. The x-ray microscope chamber is composed of a vacuum chamber, a focusing lens, a metal film target, an in-vacuum type sample holder. The pump laser pulse is focused on the metal film target with a focusing lens. The soft x-rays from the laser-induced plasma illuminates bio-specimens on the PMMA photo resist set in the in-vacuum sample holder. The photo resist is developed and the x-ray transmission image recorded on the photo re...

Near-field imaging of Ni-like silver transient collisional x-ray laser

We review our recent progress in the development of transient x-ray lasers and of their application to plasma diagnostic. The first observation of C-ray laser emission at the new PHELIX-GSI facility is reported. This TCE X-ray laser will be a promising tool for heavy-ion spectroscopy. We then present the main results obtained at the LULU-CPA facility with a compact high-resolution X-UV imaging device. This device was used to investigate the spatial source structure of the Ni-like silver transient X-ray laser under different pumping conditions. The key-role of the width of the background laser pulse on the shape of the emitting aperture is demonstrated. Finally the imaging device was used as an interference microscope for interferometry probing of a laser-produced plasma. We describe this experiment performed at APRC-JAERI.

Heat stability of Mo/Si multilayers inserted with silicon oxide layers

The Mo/Si multilayers inserted with the SiO2 layers with 2.0 nm in thickness have been proven to be thermally more stable than the conventional Mo/Si multilayer. The Mo/Si/SiO2 multilayer inserted with the SiO2 layers at the Mo-on-Si interfaces had a relatively high soft X-ray reflectivity even after annealing at 400°C. The Mo/SiO2/Si/SiO2 multilayer was structurally the most stable against annealing but the soft X-ray reflectivity of this multilayer was quite small because of the absorption of X-rays by oxygen. To minimize the deterioration of the soft X-ray reflectivity of the Mo/SiO2/Si/SiO2 multilayer with keeping the high heat stability, the optimum thicknesses of the inserted SiO2 layers have been investigated. We have found that the Mo/SiO2/Si/SiO2 multilayer having asymmetric SiO2 layer thicknesses at the Si-on-Mo interface (0.5 nm) and at the Mo-on-Si interface (1.5 nm) has thermally the most stable structure and maintains a high soft X-ray reflectivity after annealing.

Fabrication of multilayer mirrors consisting of oxide and nitride layers for continual use across the K-absorption edge of carbon

The development of multilayer mirrors for continual use around the K-absorption edge of carbon (4.4 nm) has been begun. Cobalt oxide (Co3O4), silicon oxide (SiO2), and boron nitride (BN) are found to be suitable for multilayer mirrors on the basis of theoretical calculations for wavelengths around the carbon K-absorption edge region. X-ray reflectivity curves with CuKalpha1 x rays of the fabricated Co3O4/SiO2 multilayers have sharp Bragg peaks, and the layer structures evaluated from transmission electron microscopy (TEM) observations are uniform. On the other hand, the Bragg peaks of Co3O4/BN multilayers split, and aggregated Co3O4 is observed. To improve the Co3O4 layer structure, chromium oxide (Cr2O3) was mixed into Co3O4. The mixed oxide layer structure in the Mix/BN multilayer (Mix = Co3O4 + Cr2O3) is relatively uniform, and the Bragg peaks do not split.