Journal of large-scale research facilities, 2, A46 (2016) http://dx.doi.org/10.17815/jlsrf-2-71 Published: 11.02.2016 The FemtoSpeX facility at BESSY II Helmholtz-Zentrum Berlin für Materialien und Energie * Instrument Scientists: - Dr. Niko Pontius, Helmholtz-Zentrum Berlin für Materialien und Energie, phone: : +49 30 8062-13415, email: pontius@helmholtz-berlin.de - Dr. Karsten Holldack, Helmholtz-Zentrum Berlin für Materialien und Energie, phone: +49 30 8062-13170, email: karsten.holldack@helmholtz-berlin.de - Dr. Christian Schüßler-Langeheine, Helmholtz-Zentrum Berlin für Materialien und Energie, phone: +49 30 8062-14596, email: christian.schuessler@helmholtz-berlin.de - Dr. Torsten Kachel, Helmholtz-Zentrum Berlin für Materialien und Energie, phone: +49 30 8062-12942, email: torsten.kachel@helmholtz-berlin.de - Dr. Rolf Mitzner, Helmholtz-Zentrum Berlin für Materialien und Energie, phone: +49 30 8062-12942, email: rolf.mitzner@helmholtz-berlin.de Abstract: The FemtoSpeX facility of the BESSY II storage ring is dedicated to ultrafast optical-pump and soft x-ray probe experiments. Experimental end-stations for experiments in transmission, re�ection, and di�raction geometry are available. 1 Introduction The FemtoSpeX facility of BESSY II is optimized for time-resolved experiments using polarized soft x-ray pulses (Bergeard et al., 2014; Boeglin et al., 2010; Eschenlohr et al., 2013; Holldack et al., 2010; Izquierdo et al., 2014; Radu et al., 2011; Stamm et al., 2007; Trabant, C. et al., 2013; Wietstruk et al., 2011). It consists of a high-transmission monochromator, a fs pump laser system including harmonic generation and dedicated end stations for transmission, re�ection and di�raction experiments. Mag- netic �elds up to 0.5 T for transmission and 0.2 T for other geometries are available. A new end station with higher magnetic �elds in all geometries is in preparation. For a detailed description see Holldack et al. (2014). An overview of the facility is given in Fig. 1. *Cite article as: Helmholtz-Zentrum Berlin für Materialien und Energie. (2016). The FemtoSpeX facility at BESSY II . Journal of large-scale research facilities, 2, A46. http://dx.doi.org/10.17815/jlsrf-2-71 1 http://jlsrf.org/ http://dx.doi.org/10.17815/jlsrf-2-71 http://dx.doi.org/10.17815/jlsrf-2-71 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 2, A46 (2016) http://dx.doi.org/10.17815/jlsrf-2-71 2 Monochromator The re�ection zone-plate-monochromator (ZPM) beamline at the insertion device UE56-1 has been particularly designed and optimized with high transmission optics (Holldack et al., 2014) to compensate for the relatively low �ux of 1x106ph/sec/0.1%BW of the Femtoslicing source (Khan et al., 2006). The optical layout is depicted in Fig. 2 (left). A re�ection zone plate comprises focusing as well as energy dispersion for a particular design photon energy. To cover the absorption edges of the mostly studied elements between 410 to 1333 eV, a four inch substrate hosts nine zone plate lenses (Fig. 2 right) that cover selected photon energies within that range. The images on top of the zone-plate photograph show the intensity distributions in the focus after each lens (Brzhezinskaya et al., 2013; Holldack et al., 2014). The optics is tailored to minimize pulse elongation and preserve the polarization properties of the elliptical light from the undulator. Figure 1: Optical layout of the full optical pump-soft-x-ray probe setup at the FemtoSpeX facility at the BESSY II storage ring (Holldack et al., 2014). The horizontal dimension of the entire setup is ca. 50 m. Synchronized to the 500 MHz master-oscillator driving the rf-cavities of the storage ring, a Ti:Sa oscillator seeds the two regenerative ampli�ers that are located in di�erent laser hutches. As a monochromator, either the high resolution Plane Grating Monochromator (PGM) or the high �ux Zone Plate Monochromator (ZPM) can be selected by setting a switching mirror to the corresponding position. Figure 2: Optical layout (left) of the high transmission (T ∼ 0.2) ZPM (Brzhezinskaya et al., 2013; Holl- dack et al., 2014). 2 http://dx.doi.org/10.17815/jlsrf-2-71 https://creativecommons.org/licenses/by/4.0/ http://dx.doi.org/10.17815/jlsrf-2-71 Journal of large-scale research facilities, 2, A46 (2016) 3 Pump laser system To allow for resonant pumping at high repetition rates, the laser system consists of two coupled Ti:Sa ampli�ers (Legend Elite Duo, company: COHERENT) driven by a single oscillator (Micra, COHERENT). The ampli�ers typically run at 6 and 3 kHz for the slicing- and the pump excitation, respectively, and at pulse energies of 1.8 mJ. "Slicing" of stored electron bunches is achieved by laser pulses from the �rst ampli�er resulting in ∼100 fs x-ray pulses while the second ampli�er yields pulses of ∼40 fs duration at 800 nm and as well at the second and third harmonic (400 nm and 266 nm, respectively) for the "pump" excitation of the sample. The pulse energies are su�cient to operate an optical parametric ampli�er (OPA, Opera Solo, COHERENT) providing variable pump wavelengths for sample excitation from the UV (240 nm) to the mid infrared (6µ m) wavelength range, with wave-length-dependent pulse energies. A special laser feed-in is used to couple in the pump-laser beam in to the ZPM beamline in a collinear geometry or under a small angle of 1.5°. Figure 3: Layout of the fs XMCD/XAS chamber (FemtoSpeX Magnetism). Figure 4: View of the FEMTOSPEX Scattering station. 3 http://dx.doi.org/10.17815/jlsrf-2-71 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 2, A46 (2016) http://dx.doi.org/10.17815/jlsrf-2-71 4 FemtoSpeX Magnetism (transmission) station The experimental setup for laser pump – X-ray probe on magnetic samples consists of a measurement chamber housing the magnet (up to 0.5 T parallel to the x-ray beam) and transmission sample, and the detector chamber with a fast avalanche photodiode (APD). An Al foil mounted between the chambers prevents laser light to enter the detection chamber with the APD. A load-lock allows for fast sample transfer. The layout of the instrument can be seen in Fig. 3. Technical data are summarized in Table 3. 5 FemtoSpeX Scattering station A two circle UHV di�ractometer is available for di�raction (Holldack et al., 2010; Trabant, C. et al., 2013) or re�ectivity (Izquierdo et al., 2014) studies. Sample and detector angles can be varied independently. Magnetic �elds up to 0.2 T in variable direction are available. Scattered photons are detected with avalanche photodiodes (APDs). The APDs are screened from light of the pump-laser by Al membranes and a light tight housing. Low noise ampli�cation (up to 60dB by Hamamatsu and Kuhne preampli�ers) allows besides analog pulse detection for time-correlated single-photon pulse counting. Generally sig- nals as low as ∼5 photons/sec from the sample can be detected. A photograph of the station is depicted in Fig. 4, technical data are summarized in Table 4. 6 Source The insertion device is the elliptical undulator UE56-1 with the following parameters: Type APPLE2 Location H11 Periode length 56 mm Period number 30 Minimal Energy at 1,7 GeV 58.5 eV Minimal Gap 16.6 mm Polarisation linear horizontal, linear vertical, elliptical, circular Table 1: Parameters of insertion device UE56-1. 7 Technical data Source Insertion device: UE56-1 Monochromator Re�ection Zone Plate Monochromator (RZPM) Photon energy range 410 - 1330 eV Photon energy resolution 500 (2000) Photon �ux (slicing mode) 1·106ph/sec/0.1%BW@6kHz (100 fs pulses) Divergence (horizontal, vertical) 0.2 mrad, 0.1 mrad Focus size (hor. x vert.) 100µm x 40µm (slit) Distance focus - last valve 800 mm Free photon beam No Fixed end station Yes Table 2: Technical data of the Beamline UE56-1 ZPM. 4 http://dx.doi.org/10.17815/jlsrf-2-71 https://creativecommons.org/licenses/by/4.0/ http://dx.doi.org/10.17815/jlsrf-2-71 Journal of large-scale research facilities, 2, A46 (2016) Experiment in vacuum Yes Temperature range 30 - 450 K (low-T), 130 - 750 K (variable T) Detector GaAs Photodiode, gated Avalanche Photodiode (1 ns) Manipulators Low-Temprerature (He) cryostat, variable temperature cryostat Magnetic�eld (longitudinal) 0.5 Tesla Magnetic�eld (transverse) 0.04 Tesla Table 3: Technical parameters of the FEMTOSPEX transmission station. Experiment in vacuum Yes Temperature range 6 - 400 K Detector Photon detection (see detection special features below) Manipulators x/y/z; two cycle goniometer Sample environment •In-situ sample cleaving available •Sample transfer system available •Measurements at cryogenic temperatures possible Magnetic �eld 0.2 T (variable direction) Detection special features •fs-laser synchronized gated detection (Avalanche Photo Diode) •Single photon counting detection for low intensity measurements •Laser light screened detection (>1012 attenuation) Di�ractometer features •Motor controlled two-circle •Variable detector resolution UHV < 10-9mbar (turbo-molecular pump, LN-cooling trap) Miscellaneous Laser safety protected viewports Table 4: Technical parameters FEMTOSPEX Scattering station. 5 http://dx.doi.org/10.17815/jlsrf-2-71 https://creativecommons.org/licenses/by/4.0/ Journal of large-scale research facilities, 2, A46 (2016) http://dx.doi.org/10.17815/jlsrf-2-71 References Bergeard, N., Lopez-Flores, V., Halte, V., Hehn, M., Stamm, C., Pontius, N., . . . Boeglin, C. (2014). Ultrafast angular momentum transfer in multisublattice ferrimagnets. Nature Communications, 5. http://dx.doi.org/10.1038/ncomms4466 Boeglin, C., Beaurepaire, E., Halte, V., Lopez-Flores, V., Stamm, C., Pontius, N., . . . Bigot, J. Y. (2010). Distinguishing the ultrafast dynamics of spin and orbital moments in solids. Nature, 465(7297), 458- 461. http://dx.doi.org/10.1038/nature09070 Brzhezinskaya, M., Firsov, A., Holldack, K., Kachel, T., Mitzner, R., Pontius, N., . . . Erko, A. (2013). A novel monochromator for experiments with ultrashort X-ray pulses. Journal of synchrotron radiation, 20(4), 522-530. http://dx.doi.org/10.1107/S0909049513008613 Eschenlohr, A., Battiato, M., Maldonado, R., Pontius, N., Kachel, T., Holldack, K., . . . Stamm, C. (2013). Ultrafast spin transport as key to femtosecond demagnetization. Nature Materials, 12(4), 332-336. http://dx.doi.org/10.1038/NMAT3546 Holldack, K., Bahrdt, J., Balzer, A., Bovensiepen, U., Brzhezinskaya, M., Erko, A., . . . Foehlisch, A. (2014). FemtoSpeX: a versatile optical pump-soft X-ray probe facility with 100 fs X-ray pulses of variable polarization. Journal of synchrotron radiation, 21(5), 1090-1104. http://dx.doi.org/10.1107/S1600577514012247 Holldack, K., Pontius, N., Schierle, E., Kachel, T., Soltwisch, V., Mitzner, R., . . . Weschke, E. (2010). Ultrafast dynamics of antiferromagnetic order studied by femtosecond resonant soft x-ray di�raction. Applied Physics Letters, 97(6). http://dx.doi.org/10.1063/1.3474612 Izquierdo, M., Karolak, M., Trabant, C., Holldack, K., Föhlisch, A., Kummer, K., . . . Molodtsov, S. L. (2014). Laser-induced charge-disproportionated metallic state in lacoo3. Phys. Rev. B, 90, 235128. http://dx.doi.org/10.1103/PhysRevB.90.235128 Khan, S., Holldack, K., Kachel, T., Mitzner, R., & Quast, T. (2006). Femtosecond undulator radiation from sliced electron bunches. Physical Review Letters, 97, 074801. http://dx.doi.org/10.1103/PhysRevLett.97.074801 Radu, I., Vahaplar, K., Stamm, C., Kachel, T., Pontius, N., Duerr, H. A., . . . Kimel, A. V. (2011). Transient ferromagnetic-like state mediating ultrafast reversal of antiferromagnetically coupled spins. Nature, 472(7342), 205-208. http://dx.doi.org/10.1038/nature09901 Stamm, C., Kachel, T., Pontius, N., Mitzner, R., Quast, T., Holldack, K., . . . Eberhardt, W. (2007). Fem- tosecond modi�cation of electron localization and transfer of angular momentum in nickel. Nature Materials, 6(10), 740-743. http://dx.doi.org/10.1038/nmat1985 Trabant, C., Pontius, N., Schierle, E., Weschke, E., Kachel, T., Springholz, G., . . . Schüßler-Langeheine, C. (2013). Time and momentum resolved resonant magnetic x-ray di�raction on eute. EPJ Web of Conferences, 41, 03014. http://dx.doi.org/10.1051/epjconf/20134103014 Wietstruk, M., Melnikov, A., Stamm, C., Kachel, T., Pontius, N., Sultan, M., . . . Bovensiepen, U. (2011). Hot-electron-driven enhancement of spin-lattice coupling in gd and tb 4 f ferromag- nets observed by femtosecond x-ray magnetic circular dichroism. Phys. Rev. Lett., 106, 127401. http://dx.doi.org/10.1103/PhysRevLett.106.127401 6 http://dx.doi.org/10.17815/jlsrf-2-71 http://dx.doi.org/10.1038/ncomms4466 http://dx.doi.org/10.1038/nature09070 http://dx.doi.org/10.1107/S0909049513008613 http://dx.doi.org/10.1038/NMAT3546 http://dx.doi.org/10.1107/S1600577514012247 http://dx.doi.org/10.1063/1.3474612 http://dx.doi.org/10.1103/PhysRevB.90.235128 http://dx.doi.org/10.1103/PhysRevLett.97.074801 http://dx.doi.org/10.1038/nature09901 http://dx.doi.org/10.1038/nmat1985 http://dx.doi.org/10.1051/epjconf/20134103014 http://dx.doi.org/10.1103/PhysRevLett.106.127401 https://creativecommons.org/licenses/by/4.0/ Introduction Monochromator Pump laser system FemtoSpeX Magnetism (transmission) station FemtoSpeX Scattering station Source Technical data