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To improve the stress property of multilayer optics working in extreme ultraviolet and x-ray range, mono-layer thin films of Mo, MoSi2, Si, with thickness of 100nm, and periodic multilayers of [Mo/Si] 20 , [MoSi 2 /Si] 20 , with period thickness of 20nm, were prepared by direct current magnetron sputtering method. Before and after each deposition, the radius of surface curvatures of substrates were measured using a stylus profiler and then the film stress was calculated. The measurement results indicate that, Mo, MoSi 2 and Si mono-layer thin films all shows compressive stress, while Mo/Si multilayer shows tensile stress, i.e., the film stress changes significantly during Mo/Si multilayer growth. For MoSi 2 /Si multilayer, the film stress still keeps compressive, which indicates more stable stress property.

SiC/Mg, Mo/Si and SiC/Si period multilayer mirrors were developed for solar He-II radiation at 30.4 nm. The optical stabilities of the SiC/Mg multilayer were investigated before and after space environment simulation tests for the purpose of potential application in space extreme ultraviolet observation. The multilayers are deposited by using direct current magnetron sputtering method in Ar gas atmosphere on polished fused silica substrate. Then, the reflectivities were measured at synchrotron radiation. The SiC/Mg multilayer provides the highest reflectivity of 34.0%, only 18.6% and 13.9% for Mo/Si and SiC/Si multilayer mirrors. However, Mg is known to be highly reactive and low melting point. Therefore, the thermal cycling stability test and radiation exposure experiments were performed for SiC/Mg multilayer to simulate the space environment, respectively. The testing results indicate that the reflectivity of SiC/Mg multilayer decreases slightly. After thermal cycling from -45 to 145 Celsius degree three times, the reflectivity decrease from 34.0% to 31.0%. After gamma radiation exposure, the reflectivity decreases from 31.4% to 29.4%.

X-ray grazing incidence supermirror which has extremely broad reflection band is a kind of multilayer with different each layer thickness down through the structure. The x-rays with different wavelengths or at different grazing incident angles can be reflected at different position in the supermirror structure and its band or angular response thus can be extended. These supermirrors have been developed and applied widely in many fields, especially in astrophysics. Existing approaches for designing similar neutron supermirrors are shown to provide respectable performance when applied to x-ray multilayers. However, none of these approaches consider the effects of imperfect layer interfaces and absorption in the overlying layers and all of them insist on the structure with the ratio of the layer thickness of absorbing material to the bi-layer spacing being a constant of 0.5. Adaptations of neutron designs that take these effects into account are presented in the present paper. In addition, other approaches, such as the method based on the combination of analytical and number methods, also are included and discussed in this paper. Two kinds of supermirrors with broad photon energy band or broad angular response have been designed using these different design methods. The results show that for specific applications, different optimization methods with different initial structures should be chosen accordingly to expect some overall improvement on performance of x-ray supermirrors.

a1 Institute of Precision Optical Engineering, Department of Physics, Tongji University, Shanghai 200092 eChina 2 Research Center of Laser Fusion, CAEP, P.O. Box 919-988, Mianyang 621900, China a Abstract: An auxiliary visible imaging method was introduced to solve the axial and pointing alignment of x-ray Kirkpatrick-Baez optics. Through ZEMAX simulation and x-ray imaging experiments, the axial and pointing alignment accuracy were determined to be ±300 m and ±20 m respectively. The numerical aperture of x-ray Kirkpatrick-Baez optics is rather small, so it’s impossible to adjust Kirkpatrick-Baez system by visible imaging directly. An auxiliary visible lens was designed, which was equivalent to x-ray Kirkpatrick-Baez optics on conjugate relationship and accuracy control. The comparative experiments of visible imaging and x-ray imaging indicate that this auxili ary system could meet the alignmen t accuracy of Kirkpatrick-Baez optics. Keywords: auxiliary visible imaging, x-ray Kirkpatrick-Baez optics, axial alignment, pointing alignment

A double-periodic multilayer method was proposed to test KBA system of 4.75keV using 8keV source. Alignment of angle is the key for most of grazing incidence systems in x-ray range. But for soft x-ray, strong absorption makes the alignment have to be operated in vacuum, which is difficult enough. A double-periodic multilayer was used to experiment at 8keV in air replacing 4.75keV in vacuum. This multilayer includes two parts, the top and the bottom. The top is W/B 4 C multilayer with four bilayers and 6.93nm periods. The bottom is W/B 4 C multilayer with 10 bilayers and 3.95nm periods. For 8keV energy, x-ray will penetrate through the top and reflected by the bottom. While for 4.75keV, x-ray will be reflected by the top directly. The full width of half maximum is 0.1° at 8keV and 0.3° at 4.75keV, so it is accurate enough for 4.75keV to experiment at 8keV, which was also verified by the 1-D KBA experiment. This double-periodic multilayer provides a valid solution for alignment in soft x-ray range.

Compound refractive x-ray lens is a unique device to form image of opaque object which is illuminated by x-rays. It is consisted of a lot number of placed in-line concave microlenses and works like ordinary refractive lens for visual light. In contrast to other x-ray optical devices, it could achieve satisfying resolution without complicated equipment. The spherical compound refractive x-ray lens used in this experiment is composed of 123 biconcave microlenses of 200 μm diameter. Each microlens was formed by the epoxy between two bubbles which were injected into an epoxy-filled glass capillary. There are three advantages ensuring good image quality of the lens for using in hard x-rays: (1) The epoxy (C100H200O20N, 1.08 g/cc) is composed of carbon, hydrogen and nitrogen, each of them is characterized by a low absorption coefficient for 5-30 keV x-rays. (2) Because of the nature of physics forming the bubble, the lens surface quality is extremely good. (3) The capillary makes sure that the series of unit lenses are well aligned coaxially. The lens focal length is 114 mm at 8.05 keV which is adjusted according to thick-lens analysis. X-ray images of grid mesh are compared between using a copper anode x-ray tube without filter and a synchrotron radiation source with monochromator. It could be found that the resolution and contrast are improved a lot by using monochromatic x-rays. The field of view and geometrical distortion around the edges of the field of view are reduced because of using a synchrotron radiation source. For x-ray tube as source the lens achieved a spatial resolution of 5 μm and field of view of about 700 μm. For a synchrotron radiation source, that is 3.8 μm by 2.3 μm resolution and field of view of about 316 μm by 128 μm.

Three kinds of multilayer mirrors were developed for solar observation and earth’s magnetosphere observation at Extreme Ultraviolet (EUV) wavelength region. The first one is Mo/Si multilayer mirror, designed for solar Fe-XII emission line at wavelength of 19.5nm. The reflectivities are in the range of 38.7~42.9%, measured at National Synchrotron Radiation Laboratory (NSRL), Hefei, China. Th e second high-reflective multilayer is designed for solar He-II radiation at 30.4 nm. At this wavelength, SiC/Mg multilayers were investigated, and as high as 50.0% measured reflectivity was obtained at incident angle of 10u. Aperiodic SiC/Mg multilayers were also designed for wide angular ranges of 15-22u and 12-21u. The third multilayer mirror was a dual-function mirror used for earth’s magnetosphere observation, which requires high-reflective for He-II emission line at wavelength of 30.4nm but low-reflectance at 58.4nm from ionosphere He-I emission. Using aperiodic SiC/Mg multilayer stack, the dual-function multilayer mirror was designed by genetic algorithm. Compared to periodic multilayer, the dual-function multilayer suppresses the reflectivity for He-I at 58.4nm from 2.2% to 0.1%, without loss of the reflection for He-II at 30.4nm, significantly. These multilayer mirrors were all prepared by magnetron sputte ring system in IPOE, and measured at NSRL, China. Keywords: EUV astronomical observation; multilayer; magnetron sputtering; synchrotron radiation

Multilayer mirrors are the important optical elements for astronomical observation at extreme ultraviolet region. In this article, three kinds of multilayer mirrors were introduced for solar observation and magnetosphere observation. Mo/Si multilayer mirror was fabricated for solar Fe-XII emission line at wavelength of 19.5nm. For solar He-II radiation at 30.4 nm, Mo/Si, Si/SiC, Si/C, Si/B4C and Mg/SiC multilayers were investigated, and the measurements results shows that Mg/SiC multilayer provides the highest reflectivity of 43.8% at incidence angle of 5 degree. The third multilayer mirror was a dual-function mirror used for earth's magnetosphere observation, which requires high-reflective for He-II emission line at wavelength of 30.4nm but anti-reflectance at 58.4nm from ionosphere He-I emission. Using aperiodic Mg/SiC multilayer, the dual-function multilayer mirror was designed. Compared to periodic multilayer, the dual-function multilayer suppresses the reflectivity for He-I at 58.4nm from 2.2% to 0.1%, without loss of the reflection for He-II at 30.4nm, significantly.

The present status of studies on EUV, soft x-ray and x-ray multilayer in the Institute of Precision Optical Engineering (IPOE) is briefly reviewed. With the aim of realizing a Mach-Zender interferometer working at 13.9nm, we have developed a semitransparent beam splitter with multilayer deposited on the back side of a silicon nitride membrane. On the basis of the experimental optical properties of the beam splitter, design has been performed to define the multilayer structure that provides the highest product of reflectivity and transmission. Optimized Mo/Si multilayer has been successfully deposited on the back side of a silicon nitride membrane by use of the magnetron sputtering. Measurements by means of a reflectometer in Beijing Synchrotron Radiation Facility at 13.9nm and at an angle of 7.2° provide a reflectivity of 20% and a transmission of 22%. Such a beam splitter has been used for X-ray Mach-Zender interferometer at 13.9nm. The broadband multilayer analyzer in the range between 12.4nm and 20nm is designed, and made which can deviate the Quasi-Brewster's angle several degree and show very high polarization. The main feature of our design approach is the use of an analytical solution as a starting point for direct computer search, and the desired results can be given in a reasonable time. The method can be applied in different spectral range for suitable material combination. Supermirrors with broad angular band working at different wavelength such as Cu Kα line are designed, manufactured and measured. The results show that the performance of the supermirrors is in agreement with designed data.

The periodic mulitlayer with high reflectivity and small full width at half maximum (FWHM) in hard x-ray range, while the reflectivity of non-periodic multilayer decreases and FWHM increase. Therefore, the optimum coating design must be found out as a compromise between the requirements for the reflectivity and the FWHM. We have used purely numerical techniques to design broad angular multilayer mirror in angle intervals (2.9°-3.1°), which is starting from an appropriate periodic multilayer structure. In our method, the risk of local minimization of the merit function disappears, because we refined the desired depth-distribution of the period using a direct numerical algorithm and the analytical solution as a starting point for computer calculation. The plateau reflectivity can be obtained in a few minutes. The main feature of our approach is the use of an analytical solution as a starting point for direct computer search, and the desired results can be given in a reasonable time. This technique is able to design almost any given reflectivity spectrum both energy- and angle-dependent and in a reasonable amount of time. The periodic and non-periodic W/Si multilayer for grazing incidence multilayer mirrors at the K-edge of Ti (0.275 nm) were both designed and fabricated by high vacuum DC magnetron sputtering coater model JGP560C6, and the multilayer films were characterized by X-ray reflectivity measurements on a laboratory x-ray diffractometer(XRD) and the atomic force microscope (AFM). We find good agreement of the changing trend of surface roughness between the simulation of XRD and measurement of AFM.

We designed two kinds of supermirrors composed of Carbon and Tungsten in current paper. Using Simplex Optimization method, we designed C/W supermirror with broad incident angular range (0.5°~0.9°) at Cu Kα line (λ=0.154nm). Connecting the analytical method, based on oversimplified analytical and semi-empirical formulas, with the Simplex Optimization method, we designed C/W supermirror with broad photon energy range (16~25keV), at θ=0.5°. The negative effect, due to the interfacial roughness and diffusion between the adjacent sublayers in multilayer, also emerges in simulating the practice performance of the both supermirrors. The supermirrors with broad incident angular range were fabricated by DC magnetron sputtering, because such supermirror is easy to be measured at our lab, using X-ray diffractormeter. The measured reflectivity near the first order Bragg peak is about 30% at Cu Kα line. The roughness factor is about 0.84nm by the fitting data.

The broadband x-ray supermirrors have been designed, fabricated and studied experimentally. They are intended for operating in the photon energy range from 12.4 to 20keV at the fixed grazing incident angle of 0.5°. The choice of material pairs composing a non-periodic multilayer structure is considered from the maximum achievable reflectivity and the layer structure stability. Tungsten and silicon are selected, which have the great index contrast in this energy range and are suitable for fabrication with the use of the vested coating system. The interface width determined by transmission electron microscopy (TEM) lies in the range of 0.4~0.6nm. Following a theoretical approach including analytical and numerical techniques, the designed multilayer mirrors have a practically constant reflectivity of about 24% in the desired photon energy range. The multilayers were deposited onto polished silicon substrates by a high vacuum DC magnetron sputtering system and were characterized by x-ray diffractormeter (XRD) at 8.0keV. The experiments show that the sample has about 10% reflectivity in a wide angular range; The roughness of the interface for both tungsten on silicon layer and silicon on tungsten layer was estimated to be about 0.5nm. Oscillations in the reflectivity curve proved to be larger than the expected ones. They may be caused by the random variation of the layer thickness, as well as the interdiffusion between two materials. Possibilities for further improvements of wideband multilayer mirrors are analysed as well.

The status of polarizing optical elements for the soft x-ray range is reviewed. The criteria for optimum polarization of soft x-ray reflective analyzers, transmission polarizers and phase retarders based on multilayer interference structures are presented. Following these principles, soft x-ray polarizing optical elements have been designed. Designs of broad angular and wavelength range reflective analyzers based on a combination of analytical and numerical methods are also discussed.

K-B microscope intended for the use in inertial confinement fusion experiments was designed. The microscope operates at the 8keV x-ray energy and provides the 8X magnification. The parameters of the microscope are decided by requirements of ICF experiments. Ray tracing software (Zemax) is used to simulate optical system performance. Grazing angle range on the surface of mirrors and the assembly tolerance of centre grazing incident angle were both calculated. For the working energy is 8 keV, in order to obtain sufficient reflectivity at about 1° grazing angle on each mirror, multilayer should be coated on the mirrors. Two kinds of multilayer, periodic multilayer and non-periodic multilayer (supermirror), are discussed in the paper. Take into account the grazing angle ranges on the mirrors and the grazing angle tolerance, it is necessary to have a fairly constant reflectivity over a wide angular domain. Periodic multilayer has narrow bandpass, which cannot fulfill the requirement of such wide angular domain. The non-periodic structure multilayer was designed and fabricated. The results show this kind of non-periodic multilayer can be used in K-B microscope.