Studies of polarization-sensitive, such as circular dichroism spectroscopy, spin-polarized photoelectron spectroscopy and spectroscopic ellipsometry, accurate evaluation of the polarization state of the radiation is clearly crucial, which requires polarization optical elements, such as polarizer, analyzer and phase retarder. In EUV and soft x-ray region, the closeness of the real part of the refractive index to unity, coupled with high absorption, makes the realization of polarizers such like birefringence and dichroic polarizers impossible. Periodical multilayers are commonly used in polarization study working at the quasi-Brewster angle due to their interference structures. In order to expand the narrow spectral bandwidth of the periodic multilayer, the aperiodic multilayer and lateral gradual multilayer polarizers including reflective analyzers and transmission phase retarders are utilized. In this work, we demonstrate a series of periodic, aperiodic and lateral gradual broadband multilayer polarizers with the material combinations of Mo/Si, Mo/Y, Mo/B4C, Cr/C, Cr/Sc, Cr/Ti, Cr/V and W/B4C. Different types of multilayer polarizers correspond to different energy ranges, covering the energy range of 50- 1000eV, including “water window” and the L absorption edges of Fe, Co and Ni. Polarization measurements are performed at National Synchrotron Radiation Laboratory in Hefei and Beijing Synchrotron Radiation Facility. Some of the polarizers we have developed are applied to the polarization measurements of Beam-line 3W1B of Beijing Synchrotron Radiation Facility.
Aperiodic multilayer structure and lateral gradual multilayer structure can be used to expand spectral bandwidth of multilayer polarizers. To extend application of polarization in EUV and X-ray region, two-dimensional graded multilayer structure is utilized, which is a kind of mirror with gradient period along two lateral directions and can be widely used in synchrotron radiation and polarization studies of magnetic materials. In this paper, a [Mo/Si]25 laterally graded multilayer was deposited on a 40 mm×40 mm large silicon substrate by magnetron sputtering and it was measured by grazing incidence X-ray reflection. The d-spacing gradient along X direction, from 0.0528 nm/mm to 0.116 nm/mm, was achieved by controlling the velocity of the substrate as it passes through the flux. A shaped mask controlled the d-spacing gradient in the Y-axis perpendicular to substrate translation, from 0.12 nm/mm to 0.18 nm/mm. The dspacing was 6.39 nm for the minimum and 15.65 nm for the maximum. This method is capable to prepare twodimensional laterally graded multilayer mirror in EUV and X-ray regions.
Nb-based Multilayer Laue Lens (MLL) shows high efficiency and great focusing ability at energy around 18keV theoretically. In this paper, to study the potential of Nb-based material combinations in nano-focusing, a series of Nbbased multilayers: Nb/Si, Nb/Al and Nb/Al(1%wtSi) are fabricated by using direct-current magnetron sputtering technology. Real-time stress measurement is utilized for stress analysis while the quality of multilayers is characterized by XRR and XRD. As a result, Nb presents a crystal state in the Nb/Si multilayer, and shows an asymmetric distribution at the interfaces. Both Nb films and Si films are in a strong compressive stress state, leading to a large total stress. Studies on the Nb/Al and Nb/Al(1%wtSi) multilayers show that both Al and Nb were crystalline under pure Ar sputtering conditions, resulting in large film interface width and poor film quality. The addition of 10% concentration of nitrogen in reactive sputtering can effectively suppress the crystallization of Al and change the crystalline state of Nb. However, the introduction of nitrogen greatly increased the compressive stress of Nb film, resulting in larger stress.