Research Frontiers 2014 Research Frontiers 2014 SPring-8 New Apparatus, Upgrades & Methodology 104 Major upgrade of BL25SU for soft X-ray imaging and spectroscopy using nano- and micro-focused beams Here we report a recent major upgrade of beamline BL25SU for soft X-ray spectroscopy of solid. The upgrade project started in 2012 for the purpose to optimize the beamline optics and experimental stations for advanced soft X-ray imaging and spectroscopy using nano- and micro-focused beams. Particularly, magnetic imaging with soft X-ray magnetic circular dichroism (XMCD) using a nano-focused beam (< φ 100 nm) is highly required in accordance with the element strategy project of permanent magnets, initiated by Ministry of Education, Culture, Sports, Science & Technology in Japan. The original beamline was one of the first ten beamlines constructed at SPring-8 in 1998 [1]. BL25SU has mainly been dedicated to soft X-ray photoemission spectroscopy (PES) and absorption spectroscopy for studies on the electronic and magnetic properties of solid-state materials. A helicity switching technique using a twin helical undulator light source [2] has been advantageous when measuring soft XMCD precisely. To promote high- energy-resolution PES, the beamline was designed to achieve high energy resolution of about E/ Δ E > 10,000 at a photon energy of 1 keV. During reconstruction, every optical component at the original beamline was replaced with new components. Installation of the new beamline started in Jan. 2014, and was completed in three months. After the half-year commissioning during the 2014A experimental period, the beamline has been available to users since 2014B. The new beamline consists of two branches: a microbeam with high-energy-resolution branch (branch-a) and a nanobeam with small angular divergence branch (branch-b). These can be switched using the pre- focusing mirrors (M0) shown in Fig. 1. Downstream of M0 for vertical focusing, each branch has its own horizontal focusing mirror (M1). A monochromator based on the Hettrick Underwood type [3] is composed of an entrance slit (S1), spherical mirrors (M2n), varied line spacing plane gratings (Gn), and an exit slit (S2). The specifications of each branch are listed in Table 1. The beam performance of branch-a is almost the same as the original one in terms of its energy resolution, energy range, and photon flux. This branch has three experimental stations, ST1a: t w o - d i m e n s i o n a l p h o t o e l e c t r o n s p e c t r o s c o p y Fig. 1. Photograph and schematic view of upgraded BL25SU. branch-b branch-a 5 m Horizontal focusing pre mirror (M1b) Horizontal focusing pre mirror (M1a) Plane mirror (MFa) ST1a 2D-PES M31M41a M32M42a M33M43a M31M41b Refocusing mirrors ST2a PEEM ST3a PES Fresnel zone plate ST1b Pulse-MCD ST3b nano-MCD ST2b E-MCD Entrance slit (S1b) Entrance slit (S1a) Exit slit (S2a) Exit slit (S2b) Vertical focusing pre mirrors (M0a and M0b) Spherical mirrors (M21b,M22b) Gratings (G1b,G2b) Spherical mirrors (M21a,M22a) Gratings (G1a,G2a,G3a) LASER Research Frontiers 2014 Research Frontiers 2014 105 (2D-PES) apparatus, ST2a: photoemission electron microscope (PEEM), and ST3a: photoemission electron spectroscopy (PES) apparatus. In order to obtain a micro-focused beam, refocusing mirror systems (M3n, M4na) are installed upstream of each experimental station. A high resolving power ( E/ Δ E ) of above 10,000 is confirmed by the photoemission profile at the Fermi edge of Au. The photon flux of the monochromatized beam is measured to be 10 11 photons/sec/0.01%BW using a Si photodiode. The focused beam sizes at three end stations are typically better than 10 μ m (V) × 170 μ m (H). The optical layout of branch-b is optimized for nanofocusing using a Fresnel zone plate (FZP). To increase the acceptance of FZP, the divergence angle after the exit slit is suppressed by the asymmetrical layout of the monochromator components. The divergence in a vertical direction at branch-b is about 1/10 of that at branch-a, as shown in Fig. 2. There are three experimental stations, ST1b: pulse- magnet-type XMCD apparatus (Pulse-MCD), ST2b: electromagnet-type XMCD apparatus (E-MCD), and ST3b: XMCD apparatus equipped with the FZP (nano-MCD). A refocusing mirror system (M31, M41b) is installed upstream of E-MCD. The resolving power and photon flux after the exit slit are 4,000 and 6 × 10 11 photons/sec/0.03%BW, respectively. The estimated focused beam sizes are 10 μ m (V) × 100 μ m (H) at E-MCD and φ 100 nm at nano-MCD. Yasunori Senba*, Yoshinori Kotani and Tetsuya Nakamura SPring-8/JASRI *E-mail: ysenba@spring8.or.jp References [1] Y. Saitoh et al .: J. Synchrotron Rad. 5 (1998) 542. [2] T. Hara et al .: J. Synchrotron Rad. 5 (1998) 426. [3] M.C. Hettrick and J.H. Underwood: AIP Conf. Proc. 147 (1986) 237. Table 1. Design specifications of each branch of upgraded BL25SU. Fig. 2. Optical layout (side view) of upgraded BL25SU. Branch-b Small angular divergence Energy range 120 – 2000 eV 200 – 2000 eV Resolving power E/ E > 10,000 E/ E > 3,000 Photon flux Beam Size 10 11 ph/sec 10 12 ph/sec 10 10 ph/sec @ nano-MCD 10 – 100 μ m 10 – 100 μ m φ 100 nm @ nano-MCD Branch-a High energy resolution Δ Δ 35 40 45 50 55 60 65 70 75 80 85 Distance from the source point (m) FZP M31 M41b M31 M41a M32 M42a M33 M43a S2b S2a MFa S1b S1a M2nb M2na M0b M0a M1a M1b Gnb Gna branch-a branch-b
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