title: Characteristics of a tapered undulator for the X-ray absorption fine-structure technique at PLS-II.
abstract: An in-vacuum undulator (IVU) with a tapered configuration was installed in the 8C nanoprobe/XAFS beamlime (BL8C) of the Pohang Light Source in Korea for hard X-ray nanoprobe and X-ray absorption fine-structure (XAFS) experiments. It has been operated in planar mode for the nanoprobe experiments, while gap-scan and tapered modes have been used alternatively for XAFS experiments. To examine the features of the BL8C IVU for XAFS experiments, spectral distributions were obtained theoretically and experimentally as functions of the gap and gap taper. Beam profiles at a cross section of the X-ray beam were acquired using a slit to visualize the intensity distributions which depend on the gap, degree of tapering and harmonic energies. To demonstrate the effect of tapering around the lower limit of the third-harmonic energy, V K-edge XAFS spectra were obtained in each mode. Owing to the large X-ray intensity variation around this energy, XAFS spectra of the planar and gap-scan modes show considerable spectral distortions in comparison with the tapered mode. This indicates that the tapered mode, owing to the smooth X-ray intensity profile at the expense of the highest and most stable intensity, can be an alternative for XAFS experiments where the gap-scan mode gives a considerable intensity variation; it is also suitable for quick-XAFS scanning.
authors.affiliation: Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang 790-834, Republic of Korea.
authors.forename: Nark-Eon
authors.initials: NE
authors.lastname: Sung
authors.affiliation: Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang 790-834, Republic of Korea.
authors.forename: Ik-Jae
authors.initials: IJ
authors.lastname: Lee
authors.affiliation: Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang 790-834, Republic of Korea.
authors.forename: Sung-hoon
authors.initials: SH
authors.lastname: Jeong
authors.affiliation: Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang 790-834, Republic of Korea.
authors.forename: Seen-Woong
authors.initials: SW
authors.lastname: Kang
keywords: X-ray absorption fine structure; gap-scan mode; high-order harmonic; tapered mode; undulator