Soft X-ray Scattering and Spectroscopy (SSS) beam line in PAL-XFEL
Soonnam Kwon
(Staff Scientist, PAL-XFEL, POSTECH, Korea)
The Soft X-ray Scattering and Spectroscopy(SSS) beam line provides the XFEL with anenergy range of 0.25 ~ 1.2 keV, at a repetition
rate of 60 Hz with pulse width as short as 90 fs.
SSS experimental instruments are intended tobe relevant to diverse scientific programs
related to spectroscopy and scattering in abasic research area of solid state materials
science. The beam line consists of offset mirrors,a varied line spaced grating monochromator,and Kirkpatrick-Baez (KB) refocusing optics, as
shown in FIG1. The monochromator is designed
to have fundamental resolving power of 10000.
Using KB optics, photon beams with small
divergence < 1 mrad, and small size < 5 μm
can be provided all the entire range of photonenergy.
SSS experimental instruments aim to provide
diversescientificprograms

relatedtoFIG. 1 Top: picture of the endstation, bottom:
schematic diagram of the endstation.

spectroscopy and coherent scattering. Two
different end stations will be constructed. EndThe design of the RIXS spectrometer is based

Station 1 (already setup now) will be used foron that of Dr. Yi-de Chung at advanced lightCoherent X-ray diffraction imaging (CXDI), andsource (ALS). It is composed of three parts: aresonant inelastic X-ray scattering (RIXS). End

spherical pre mirror, a plane grating (2400Station 2 (not completed yet) will be used forlines/mm), and an area CCD detector. This

resonant soft X-ray scattering (RSXS).

spectrometer is designed to diffract photons ofXPS, RIXS, and CXDI experiments can be200 eV ≤ E ≤ 1200 eV with an expected energy

performedsample

resolving power of 1500 at 1000 eV. FIG. 2 topchamber (FIG.1). The experimental chambershows the results of test experiment using CeO2.

(FIG. 1bottom) can provide three different

The typical charge transfer (CT), f-f excitation,

photon sources and three different detectors;

and elastic emissions can be clearly seen. The

XFEL, optical laser, and EUV can be chosen as

elastic peak shows FWHM of 0.6 eV, which ispump or probe beam. PI-MTE 2048B is used asthethe CXDI detector, and a Newton DO940P-BN

spectrometer.

independentlyis used as an RIXS detector.

inonemeasureof

resolvingpowerofthewhich SiNx film was pumped by XFEL and thechange of reflectivity of SiNx by 400 nm opticallaser was recorded as a function of delay
between the two pulses. The FWHM ofmodulated Gaussian peak is estimated to bearound 320 fs. This value contains total timing
coincidence including pulse widths of XFEL andLaser, timing jitter, XFEL pulse stretching by thegrating, and time broadening by SiNx itself.
Even though the other end stations andFIG. 2 Top: RIXS spectrum of CeO2 at incident
photon energy of 884 eV. Bottom: X-ray pump400 nm optical laser probe experiment showing
total coincidence timing of the beamline.
Most of the XFEL experiments involve pumpprobe process, in which timing between pumpexperimental

apparatus

arestillunderdevelopment, this beamline has undertook
three user experiments in 2017. And the 2018beam time proposal is open to global users.
(http://pal.postech.ac.kr/)

and probe pulses is important. FIG. 2 bottom
shows the typical pump-probe experiments, inAfter obtaining Ph.D. from Dept. Physics of Yonsei Univ. in 2001, heelaborated on electronic properties of diversity of organic semiconductors
both in industry and in university as a research professor.

Since 2013, hehas been developing x-ray optics and experimental instruments for soft Xray beam line of PAL-XFEL. His main research interest is the investigation ofthe dynamics of electronic structure of nano-sized materials using
photoemission spectroscopy and inelastic resonant x ray scattering (RIXS)