Multilayer optics for the EUV and soft X-rays

The demand to enhance the optical resolution, to structure and observe ever smaller details, has pushed the way towards the EUV and soft X-rays. Induced mainly by the production of more powerful electronic circuits with the aid of projection lithography, optics developments in recent years can be characterized by the use of electromagnetic radiation with smaller wavelength. The good prospects of the EUV and soft X-rays for next generation lithography systems (λ=13.5 nm), microscopy in the “water window” (λ=2.3～4.4 nm), astronomy (λ=5～31 nm), spectroscopy, plasma diagnostics and EUV/soft X-ray laser research have led to considerable progress in the development of different multilayer optics. Since optical systems in the EUV/soft X-ray spectral region consist of several mirror elements a maximum reflectivity of each multilayer is essential for a high throughput. This paper covers recent results of the enhanced spectral behavior of Mo/Si, Cr/Sc and Sc/Si multilayer optics.

The Soft X-ray Imager(SXI)on the SMILE Mission

The Soft X-ray Imager(SXI)is part of the scientific payload of the Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)mission.SMILE is a joint science mission between the European Space Agency(ESA)and the Chinese Academy of Sciences(CAS)and is due for launch in 2025.SXI is a compact X-ray telescope with a wide field-of-view(FOV)capable of encompassing large portions of Earth’s magnetosphere from the vantage point of the SMILE orbit.SXI is sensitive to the soft X-rays produced by the Solar Wind Charge eXchange(SWCX)process produced when heavy ions of solar wind origin interact with neutral particles in Earth’s exosphere.SWCX provides a mechanism for boundary detection within the magnetosphere,such as the position of Earth’s magnetopause,because the solar wind heavy ions have a very low density in regions of closed magnetic field lines.The sensitivity of the SXI is such that it can potentially track movements of the magnetopause on timescales of a few minutes and the orbit of SMILE will enable such movements to be tracked for segments lasting many hours.SXI is led by the University of Leicester in the United Kingdom(UK)with collaborating organisations on hardware,software and science support within the UK,Europe,China and the United States.

Space Soft X-ray and EUV Optics in CIOMP

1 Introduction Since the early of 1980’s,the studies of soft X-ray and EUV optics have been implemented in CIOMP (Changchun Institute of Optics,Fine Mechanics and Physics)．So far,the research system of soft X-ray and EUV optics has been founded including sources,ra- diometry,testing and manufacturing of the super smooth mirror and multilayer coating mirror fabrication．Based on the above technologies,we started to develop the soft X-ray and EUV optical system such as a space EUV solar telescope and a EUV imager．

Thermal Diffusion of Si Atoms at the Interface of Mo/Si Bilayers Studied with a Soft X-ray Emission Microscope

Thermal diffusion of Si atoms at the interface in Mo/Si multilayers was observed with an imaging type soft X ray emission microscope developed by us. It was possible to observe the diffusion with 0.2nm depth resolution in the direction normal to the interface by comparing the emission intensity for exactly the same position. The diffusion coefficient of Si atoms in Mo at 600℃ was roughly estimated to be 6.0×10 17 cm 2/s.

Present Status of EUV Interferometer Development at the Research Center for Soft X-ray Microscopy

A new interferometer for extreme ultraviolet (EUV) radiation with a laser produced plasma (LPP) laboratory source is under construction. The LPP source is operated with a Sn solid rod target on which pulsed YAG laser is focused to produce high temperature plasma emitting EUV radiation. The source is equipped with a newly designed debris stopper protecting a condenser multilayer mirror from the particle debris of the target. The condenser mirror focuses the light onto an EUV beam-splitter to form transmitted and reflected paths for producing interference fringes of a sharing type. The optical configuration is of a common path based on a triangular path type with a focusing at the beam-splitter, which is enabled to produce fringes by a low coherence radiation with a standard optical quality beam-splitter. The fringes are recorded by an imaging plate with pixels as small as 25μm. The dynamic range of linearity in detection of the EUV light was found to be more than 10 4 with sensitivity of 10 4 photons/pixel, enough for the purpose of interferogram recording, possibly with one laser shot.

Soft X-ray optical multilayer mirrors

The current research on the structure design, characterization and structural stability of soft X-ray optical multilayermirrors is reviewed and further studies on the currently existing problems and the possible solutions are made.

Preliminary investigations of a potential optics system for wideband X-ray telescopes

We present preliminary investigations of a potential optics system for wideband X-ray telescopes.The optical design adopts the conical approximation of the Wolter-I configuration and a combination of multilayer coatings and silicon pore optics.The total number of mirror modules is 79,distributed in 8 rows with the radii at the intersection plane between 250 mm and 500 mm.The optimization of the total effective area using the figure of merits method suggests that the focal length is 30 m and the mirror coating is a combination of the W/Si and Pt/C multilayers.This fulfills the on-axis effective area requirements of 2000 cm^(2) at 10 keV and 300 cm^(2) at 60 keV and provides a broad energy response between 3 keV and 78.4 keV.With the current geometry and coating compositions,we implement a mass modeling of the telescope in Geant4 to predict mirror performances via the ray-tracing algorithm,including the angular resolution and effective area.With the presumed metrological data as input,this can provide precision and finishing requirements for the manufacture of optics.This work demonstrates the feasibility of combining multilayer coatings and silicon pore optics for potential use in wideband X-ray telescopes and advances the development and progress of such missions.

TEM and Raman scattering investigation of carbon in annealed Co/C soft X-ray multilayers

The structures of the carbon sublayers in the annealed Co/C soft X-ray multilayers fabricated by using a dual-facing-target sputtering system have been characterized by transmission electron microscopy (TEM) and Raman spectroscopy (RS). The results suggest that the structural variations in the carbon layers can be roughly divided into three stages, i e ordering, crystalline and grain growth stages. At the ordering stage with annealing temperatures below 400℃, the amorphous carbon layers change from ones of bond-angle disorder and fourfold-bonding only to ones of threefold-bonding. At the crystalline stage, the amorphous carbon layers in the as-deposited multilayers crystallize to graphite crystallites in the annealing temperature range of 500-600℃ At the grain growth stage, the specimens are annealed at temperatures higher than 700℃ A growth in the graphite crystallite dimensions is observed, which is consistent with the TEM results

Preparation and structural stability investigation of CoN/CN soft X-ray multilayers

The structural stability of heat-treated CoN/CN soft X-ray multilayers fabricated by dual-facing-target sputtering has been investigated by using complementary measurement techniques.The high temperature annealing results imply that the destructive threshold of the Co/C multilayers is improved by 100-200 degrees centigrade through doping with N.The low-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period expansion of the multilayers is only 4 % at 400℃,and the interface pattern still exists even if they were annealed at 700℃.The Raman spectra analyses give the evidence that the formation of the sp bonding in the CN sublayers can be suppressed effectively by doping N with atoms,and thus the period expansion resulting from the changes in the density of CN layers can be decreased considerably.The X-ray photoelectron spectra analyses present the information of the existence of the strong covalent bonding between C and N atoms,and the ionic bonding between Co and N atoms,which can slow down the tendency of the structural relaxation.The interstitial N atoms decrease the mobility of Co atoms,and thus the fee-Co and hep-Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420℃,leading to the suppression of the grain growth.

Aging effect of Co/C soft X-ray multilayer mirrors BAI Haili, JIANG Enyong, TIAN Renyu and WANG Cunda

MULTILAYER X-ray mirrors are of one-dimensional period structures consisting of alternating layers of materials of high- and low-refractive index. In the applications of soft X-ray multilayer mirrors, such as microscopy, astronomy and microlithography, high reflectivity is so important that it is necessary to know if the multilayers in use show aging effects, e.g. reflectivity changing with time. In this study, the aging effects of Co/C multilayers are investigated,

Design and fabrication of soft X-ray multilayer for broadband reflection

A random method used for improving light throughput of a soft X-ray multilayer has been developed in the 18-20 nm spectral region, based on the traditional theory of periodic multilayer, and an 8% gain in integrated reflectance is obtained. The ensemble calculation is presented at the same time, and the multilayer is fabricated by magnetron sputtering.

Interdiffusion in Co/C soft X-ray multilayer mirrors

The observation of structural changes in multilayers （MLs） has been used to study the interaction of materials at interface under nonequilibrium conditions, and to measure atomic diffusion rate and activation energies for compound formation. Cook and Hilliard have developed a technique which allows the measurement of small interdiffusivities down to 10-27m2·s-1 by X-ray diffraction. Previous measurements are concentrated mainly on the crystalline metallic multilayers and amorphous metallic multilayers. To our knowledge, few interdiffusion measurements have been carried out for amorphous metallic-metalloid multilayers. As effective soft X-ray mirrors, Co/C multilayers have been successfully used in an X-ray telescope. Therefore, this note aims to report the interdiffusion of sputtered

Multilayer-based soft X-ray polarimeter at the Beijing Synchrotron Radiation Facility

A compact high precision eight-axis automatism and two-axis manual soft-ray polarimeter with a multi- layer has been designed, constructed, and installed in 3WlB at the Beijing Synchrotron Radiation Facility （BSRF）. Four operational modes in the same device, which are double-reflection, double-transmission, front-reflection-behind- transmission and front-transmission-behind-reflection, have been realized. It can be used for the polarization analysis of synchrotron radiation. It also can be used to characterize the polarization properties of the optical elements in the soft X-ray energy range. Some experiments with Mo/Si and Cr/C multilayers have been performed by using this polarimeter with good results obtained.

北京同步辐射软X射线偏振测量装置及其应用

在北京同步辐射装置(BSRF)设计建造了一套基于多层膜偏振元件的软X射线偏振测量分析装置,可工作在双反、双透、前反后透和前透后反四种工作模式,既可作为偏振测量装置,用于同步辐射光束线和多层膜偏振元件偏振特性测量,也可作为通用反射率计,用于多层膜和薄膜的反射或透射率测量,又可用于磁性材料的磁光效应研究等。利用自行研制的装置和光学元件对BSRF的3W1B光束线的偏振特性进行了系统的测量。测量结果指出,在206 eV时,输出光的线偏振度从起偏前的0.585上升到起偏后的0.995,同步光的线偏振度得到极大改善。利用非周期宽带Mo/Si多层膜开展了铁磁性材料的磁光法拉第效应测量,获得了Ni薄膜3p边附近(60–70 eV)的法拉第旋转角度,最大偏转角度在65.5 eV和68 eV分别为1.85±0.19°和–0.75±0.09?。

X射线光学多层膜的研究

介绍X射线光学多层膜的构成原理、制作、测量方法及在超高真空系统中的研制技术。

非理想软X射线光学多层膜的掠入射镜向反射率

对实际软Ｘ射线光学多层膜中普遍存在的主要非理想因素（层厚漂移、界面粗糙度和界面扩散）进行了定量描述. 基于动力学光学理论，计算了上述非理想因素对软Ｘ射线光学多层膜的掠入射镜向反射率的影响结果表明：层厚的随机漂移使反射率、尤其是高级反射率降低；累积层厚漂移破坏了多层膜的长程有序性，使反射峰展宽；界面扩散和界面粗糙度使反射率降低，对高级反射率的影响更甚，但二者并不破坏多层膜的长程有序性，所以反射峰的宽度不变；界面扩散和界面粗糙度对反射率影响的机制不同；在界面扩散宽度和界面粗糙度相等的情况下，界面粗糙度使反射率下降显著．用模拟退火 Ｍｏｎｔｅ－Ｃａｒｌｏ方法对 Ｃｏ／Ｃ软Ｘ射线光学多层膜进行了结构评价．该方法能避免复杂的求导运算，在软Ｘ射线光学多层膜的结构评价中具有较强的实用性．

光学薄膜的发展及应用前景

光学薄膜作为一类重要的光学器件,在现代光学、光电子学、光学工程和其他一些重要的技术领域中应用越来越广泛。伴随着科学技术的不断发展,光学薄膜及光学薄膜技术也正在迅猛的发展,并在其他科学技术领域中应用广泛,取得了相当大的成就。金刚石及类金刚石膜、软X射线多层膜等新型光学薄膜相继问世,新型光学薄膜技术与传统光学薄膜技术有机的结合,形成光学薄膜蓬勃发展的局面。

用光学全息方法研制软X射线Bragg-Fresnel光学元件

介绍了软X射线Bragg Fresnel光学元件的特点 ,并以磁控溅射法制备多层膜 ,再采用光学全息方法在涂有光刻胶的多层膜表面上形成波带片图形 ,通过显影。

A Lunar-based Soft X-ray Imager(LSXI)for the Earth's magnetosphere

We propose to use the Moon as a platform to obtain a global view of Earth's magnetosphere by a Lunar-based Soft X-ray Imager(LSXI).LSXI is a wide field-of-view Soft X-ray telescope,which can obtain X-ray images of Earth's magnetosphere based on the solar wind charge exchange(SWCX)X-ray emission.Global perspective is crucial to understand the overall interaction of the solar wind with magnetosphere.LSXI is capable of continuously monitoring the evolution of geospace conditions under the impact of the solar wind by simultaneous observation of the bow shock,magnetosheath,magnetopause and cusps for the first time.This proposal is answering the call for the Chinese Lunar Exploration Program Phase IV.

Space solar telescope in soft X-ray and EUV band

In this paper we have reviewed our achievements in soft X-ray and extreme ultraviolet (EUV) optics. Up to now, the research system of soft X-ray and EUV optics has been established, including light sources, detectors, calibrations, optical testing and machining of super smooth mirrors, and fabrications of multilayer film mirrors. Based on our achievements, we have developed two types of solar space telescopes for the soft X-ray and EUV space solar observations. One is an EUV multilayer normal incident telescope array including 4 different operation wavelength telescopes. The operation wavelengths of the EUV telescope are 13.0, 17.1, 19.5 and 30.4 nm. The other is a complex space solar telescope, which is composed of an EUV multilayer normal incident telescope and a soft X-ray grazing incident telescope. The EUV multilayer normal incident telescope stands in the central part of the soft X-ray grazing incident telescope. The normal incident telescope and the grazing incident telescope have a common detector. The different operation wavelengths can be changed by rotating a filter wheel.