Mingqi Cui

Complete polarization analysis of extreme ultraviolet radiation with a broadband phase retarder and analyzer

The polarization state of the BESSY UE56/1-PGM beamline radiation in the broad wavelength range of 12.7–15.5nm was measured using a molybdenum/silicon transmission phase retarder and a reflection analyzer with aperiodic multilayer interference structures, which can broaden the spectral response of these optical elements. The characteristics of the circular polarized undulator radiation, as well as the polarization properties of the two polarizing elements, were determined by a complete polarization analysis. Furthermore, the polarization of the radiation as a function of the undulator shift setting was also measured at the wavelength of 13.1nm by use of the broadband phase retarder-analyzer pair.

High reflectivity multilayer for He-II radiation at 30.4 nm

SiC/Mg and B(4)C/Mo/Si multilayers were designed for He-II radiation at 30.4 nm. These multilayers were prepared by use of a direct current magnetron sputtering system and measured at the National Synchrotron Radiation Laboratory, China. The measured reflectivities were 38.0% for the SiC/Mg multilayer at an incident angle of 12 deg and 32.5% for the B(4)C/Mo/Si multilayer at 5 deg, respectively. A dual-function multilayer mirror was also designed by use of the aperiodic SiC/Mg multilayer. Annealing experiments were performed to investigate the thermal stability of the SiC/Mg multilayer. The interface of the SiC/Mg multilayer before and after annealing was studied by electron-induced x-ray emission spectra, which evidences the absence of thermal reaction products at the interfaces after annealing.

The Soft X‐ray Polarimeter and Applications at BSRF

A novel compact polarimeter for the use in soft x‐ray region having high‐precision eight‐axis automatically driven and two‐axis manually driven equipped with multilayer polarizers was developed at the Beijing Synchrotron Radiation Facility (BSRF). The polarimeter was designed to utilize reflection and transmission geometry. Four operational modes have been designed and carried out with the polarimeter. Some experiments have been performed by using this polarimeter with various modes.

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 multilayer has been designed, constructed, and installed in 3W1B 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.

Fabrication of the beam splitters for soft X-ray laser application

The soft X-ray interferometry is completed by the Mach-Zehnder interferometer using a soft X-ray laser, and it is also an important method to measure the electron densities of a laser-produced plasma near the critical surface. It is apparently demonstrated in this paper that the incident angle of each optical element in the soft X-ray Mach-Zehnder interferometer should be near normal incidence based on the polarized characteristics of the soft X-ray multilayers, and the product of reflectivity and transmission of the beam splitter should be taken as a standard of design according to the structure of the soft X-ray Mach-Zehnder interferometer. The beam splitters used in the soft X-ray interferometry at 13.9 nm are fabricated using the ion beam sputtering. The figure error of the beam splitter has reached the nanometer magnitude, in which the product of reflectivity and transmission of the beam splitter is more than 1.6%.

Periodic Co/C, Cr/C, and CoCr/C soft x-ray multilayers prepared by N reactive sputtering

Lightweight Asymmetry and Magnetism Probe project (LAMP) was proposed in China to observe the polarized radiation around 250 eV emitted by soft X-ray celestial sources, like puslars, active galactic, black hole binaries, etc. To produce the high efficiency soft X-ray polarizer for LAMP, we are developing Co/C, Cr/C, CoCr/C X-ray multilayers using magnetron sputtering and reactive sputtering with nitrogen. Hard X-ray grazing incidence reflectometry (GIXR) and soft X-ray reflectance measurements were used to study the interface and microstructure of different multilayers. In comparison to the multilayers deposited by normal magnetron sputtering, reactively-sputtered multilayers show higher reflectivity around 250 eV and lower interfacial roughness. As a result, Co/C, Cr/C, CoCr/C multilayers with smaller period can be made with respect to the multilayer fabricated using non-reactive sputtering. The X-ray performance of reactive sputtered Co/C and CoCr/C multilayers can be further improved by optimizing the deposition process.

Extreme ultraviolet multilayer mirrors for astronomical observation

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 earths 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.

Effect of background pressure on Co/C multilayers

Co/C multilayers with a period thickness of 3.54 nm and 30 bilayers were deposited by direct current magnetron sputtering with different background pressures. The effects of residual background gases were investigated. The films were characterized by using grazing incidence hard x-ray reflectivity, soft x-ray reflectivity, and x-ray photoelectron spectroscopy. The results indicate that the x-ray reflectivity of Co/C multilayers decreases with increasing background pressure as well as the increasing interlayer roughness. The inclusion of more residual background air increases the interdiffusion of Co and C layers.

Fabrication of Multilayer Reflective Mirrors for Soft X-Ray Laser Working at the Wavelength of 4.48 nm

Near normal incident high reflective and polarized multilayer mirrors were designed and fabricated for Ni-like Ta X-ray laser working at the wavelength of 4.48 nm. The influence of the imperfect interface on the reflectivity of the multilayer was simulated. Using the direct current magnetron sputtering technique, the Cr/C and Cr/Sc multilayers were deposited. Then, the layer thickness and structure of the multilayer were measured and fitted by an X-ray diffractometer. The reflectivities of these multilayers were measured on the beam line UE56/1-PGM at BESSY-II. At grazing incident angle of 85°, the measured peak reflectivities were 7.50% and 6.12% for Cr/C and Cr/Sc multilayer mirrors, respectively. At the grazing angle of 44°, the s-reflectivity is 13.61% for Cr/C multilayer polarizer. The measurement and simulation results suggest that the interface roughness strongly reduces the reflectivity of the multilayers. Thus, there is still a potential for improvement by introducing diffusion barriers and using more perfect substrate.