Journal of large-scale research facilities, 2, A89 (2016) http://dx.doi.org/10.17815/jlsrf-2-82 Published: 15.11.2016 XPP: X-ray Pump Probe station at BESSY II Helmholtz-Zentrum Berlin für Materialien und Energie * Instrument Scientists: - Dr. Matthias Reinhardt, Helmholtz-Zentrum Berlin für Materialien und Energie, phone: +49 30 8062 - 14712, email: matthias.reinhardt@helmholtz-berlin.de - Dr. Wolfram Leitenberger, Universität Potsdam, phone: +49 30 8062 - 14712, email: leitenberger@uni-potsdam.de Abstract: The X-ray Pump-Probe (XPP) experimental station predominantly aims at investigating hard and soft matter under a broad range of ambient conditions using time-resolved X-ray diffraction. 1 Introduction The X-ray Pump-Probe (XPP) experimental station is dedicated to time-resolved material research of solid-state and soft condensed matter systems. The station utilizes a fiber-based femtosecond laser sys- tems that yields optical pulses of 250 fs duration and 10 µJ pulse energy at variable repetition rates of up to 1.25 MHz. The sample environment comprises an in-vacuum 4-circle diffractometer with cryostat for cooling down to 20 K. Diffracted X-ray photons are detected with a hybrid pixel area detector allowing for ultrafast reciprocal space mapping. Optical pump light and the X-ray probe pulses enter the vacuum chamber on quasi collinear beam paths. The goniometer axes allow for scanning of a large reciprocal space volume while preserving the illumi- nated pump area on the sample surface. Hence, several in-plane and out-of-plane diffraction peaks can be measured under comparable optical pump conditions. *Cite article as: Helmholtz-Zentrum Berlin für Materialien und Energie. (2016). XPP: X-ray Pump Probe station at BESSY II. Journal of large-scale research facilities, 2, A89. http://dx.doi.org/10.17815/jlsrf-2-82 1 http://jlsrf.org/ http://dx.doi.org/10.17815/jlsrf-2-82 http://dx.doi.org/10.17815/jlsrf-2-82 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 2, A89 (2016) http://dx.doi.org/10.17815/jlsrf-2-82 The setup is specifically optimized for experiments at high laser repetition rates where fast heat removal from the excited samples is required. Two cooling options are provided: 1. The sample holder is connected to a 4 K cryostat via flexible copper wires. While allowing full mechanical flexibility the sample can be cooled down to temperatures of less than 20 K without laser excitation. Exciting the sample with the high repetition laser system leads to a typical static temperature increase of up to 100 K depending on laser power and sample heat conduction. 2. At ambient pressure the excited sample surface can be directly cooled with a cold nitrogen jet. The temperature range of the coolant extends from room temperature to 90 K. This configuration can either be used for efficient heat removal from the excited sample surface or for real cooling to cryogenic temperatures. Samples are excited by ultrafast optical pulses emitted from an ytterbium-doped fiber laser. Laser param- eters are listed in Table 1. Alternative excitation concepts are currently developed, e.g., sample excitation with ultrashort current or voltage pulses. The XPP-station is fully operational since April 2015. 2 Instrument application • Thermal transport in nanoscale systems • Coherent lattice dynamics • Electronic and magnetic coupling to the crystal structure in multiferroic systems • Phase transitions and phase change materials • New methods for time-resolved XRD 3 Technical data The laser source is a multi-stage ytterbium-doped oscillator - amplifier system (Impulse, Clark-MXR). It is synchronized to the RF-signal of the storage ring with accuracy better than 5 ps. The main laser parameters are: Repetition Rate Adjustable by user from 200 kHz to 25 MHz Pulse Energy Adjustable by user: 0.8 µJ @ frep > 2 MHz < 25 MHz 10 µJ @ frep < 2 MHz Average Output Power Adjustable by user: max. 10 W frep = 2 MHz typical operation: 2 W frep = 208 kHz Pulse Duration 250 fs Center Wavelength 1030 nm Pump probe delay up to 5 µs frep = 208 kHz with 4 ps resolution Table 1: Specification of the excitation laser. Specifications of the Beamline and of the sample environment are listed in Table 2. The diffractometer in the vacuum vessel is shown in Figure 1. 2 http://dx.doi.org/10.17815/jlsrf-2-82 https://creativecommons.org/licenses/by/4.0/ http://dx.doi.org/10.17815/jlsrf-2-82 Journal of large-scale research facilities, 2, A89 (2016) Monochromator U41-FSGM Experiment in vacuum Yes Temperature range <20 K to room temperature Detector • Dectris, Pilatus 100k hybrid pixel area detector • Home-build fast scintillator (trise < 1 ns) + time-correlated SPC • CyberStar Scintillator Detector • Energy dispersive detector: (XFlash, Roentec; ∆E/E ≈ 170 eV @8 keV) Manipulators Diffractometer layout: 3 sample circles: Circle With Cryostat Without Cryostat ω -3° - 33° 0° - 90° ϕ -10° - 100° 0° - 360° χ 0° - 180° 0° - 180° 1 detector circle (Θ): 0° - 110° x-y-z- translation for sample positioning adjustment of optical pump - X-ray probe overlap via transversal positioning of focusing lens Table 2: Specification of the sample environment. Figure 1: Diffractometer in the vacuum vessel. 3 http://dx.doi.org/10.17815/jlsrf-2-82 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 2, A89 (2016) http://dx.doi.org/10.17815/jlsrf-2-82 References Gaal, P., Schick, D., Herzog, M., Bojahr, A., Shayduk, R., Goldshteyn, J., . . . Bargheer, M. (2012). Time-domain sampling of x-ray pulses using an ultrafast sample response. Applied Physics Letters, 101(24), 243106. http://dx.doi.org/10.1063/1.4769828 Gaal, P., Schick, D., Herzog, M., Bojahr, A., Shayduk, R., Goldshteyn, J., . . . Bargheer, M. (2014). Ultrafast switching of hard X-rays. Journal of Synchrotron Radiation, 21(2), 380–385. http://dx.doi.org/10.1107/S1600577513031949 Herzog, M., Bojahr, A., Goldshteyn, J., Leitenberger, W., Vrejoiu, I., Khakhulin, D., . . . Bargheer, M. (2012). Detecting optically synthesized quasi-monochromatic sub-terahertz phonon wavepackets by ultrafast X-ray diffraction. Applied Physics Letters, 100(9), 094101. http://dx.doi.org/10.1063/1.3688492 Navirian, H. A., Schick, D., Gaal, P., Leitenberger, W., Shayduk, R., & Bargheer, M. (2014). Ther- moelastic study of nanolayered structures using time-resolved X-ray diffraction at high repetition rate. Applied Physics Letters, 104(2), 021906. http://dx.doi.org/10.1063/1.4861873 Shayduk, R., Herzog, M., Bojahr, A., Schick, D., Gaal, P., Leitenberger, W., . . . Bargheer, M. (2013). Di- rect time-domain sampling of subterahertz coherent acoustic phonon spectra in SrTiO3 using ultrafast X-ray diffraction. Physical Review B, 87, 184301. http://dx.doi.org/10.1103/PhysRevB.87.184301 Shayduk, R., Navirian, H., Leitenberger, W., Goldshteyn, J., Vrejoiu, I., Weinelt, M., . . . Bargheer, M. (2011). Nanoscale heat transport studied by high-resolution time-resolved X-ray diffraction. New Journal of Physics, 13(9), 093032. 4 http://dx.doi.org/10.17815/jlsrf-2-82 http://dx.doi.org/10.1063/1.4769828 http://dx.doi.org/10.1107/S1600577513031949 http://dx.doi.org/10.1063/1.3688492 http://dx.doi.org/10.1063/1.4861873 http://dx.doi.org/10.1103/PhysRevB.87.184301 https://creativecommons.org/licenses/by/4.0/ Introduction Instrument application Technical data