Experimental station Bernina

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Femtosecond X-Ray Pump-Probe Diffraction and Scattering Electronic and Magnetic Ordered Crystalline Materials

Experimental Station B (ESB) is designed for femtosecond pump-probe experiments in condensed matter and material science, employing photon-in photon-out techniques in the energy range 4.5 – 12.4 keV [1,2]. It includes a femtosecond optical laser system to generate a variety of pump beams (from the UV up to the THz range), a X-ray optical scheme to tailor the X-ray probe beam, shot-to-shot diagnostics to monitor the X-ray intensity and arrival time, and two endstations operated at a single focus position with spot size of 2-200 μm:

  1. ) The XPP-XRD station (see Fig 1.) is dedicated to X-ray pump-probe (XPP) resonant and non-resonant X-ray diffraction (XRD) experiments [3-5]. It consists of a heavy load six-circle Kappa-diffractometer with dual-detector arm carrying a 4M 2D pixel detector (Jungfrau) [6] and a polarization analyzer stage with point detector, respectively. Experiments for samples under a variety of environmental conditions are done by replacing the in-air Kappa-goniometer by custom built sample environmental modules.
  2. ) The XPP-GPS station (see Fig 1.) is a general purpose station for XPP experiments in non-scanning mode. It consists of a heavy load sample goniometer and a robot detector arm carrying a 16M 2D pixel detector (Jungfrau) [7]. By swapping stages, a variety of sample environmental modules can be accommodated. The robot detector arm is mounted to the ceiling and can be retracted up to 3 m downstream (3.7 m from the focal position) to enable coherent diffraction and SAXS experiments.

Until endstation ESC becomes operational, fixed target protein crystallography will be offered at XPP-GPS [8]. A module is being developed for serial femtosecond crystallography at 100 Hz of 3-D micro-crystals of size < 5 μm in a cryo/in-air or He-environment.

Pump options

For pump-probe experiments several pumping options (UV/NIR/FIR) are available. Special emphasis is given to provide intense pulses in the midIR/THz range a very important wavelength range since it permits the selective control of material properties by addressing low energy excitations such as electro-magnons [4], spin waves [9] or phonons [10]. An optical parametric amplifier (OPA) with subsequent difference frequency generation covers the spectral range from 1100 to >15000 nm. The same output is used to generate intense THz pulses in organic crystals with field strengths exceeding 1 MV/cm [11] and pulse energy up to 10 μJ in the frequency range 1-10 THz. Very short pulses (< 10 fs) are available at 800 nm by pulse compression in a hollow core fibre [12]. To compensate for drifts in the amplifier system, a laser arrival time monitor (LAM) will be installed directly after the compressor. A variety of laser diagnostics will provide all relevant laser parameters for the user.

X-ray timing diagnostic

The X-ray timing diagnostic setup is installed in the ESB hutch upstream of the diamond/Si solid state attenuator (SSA). Two different techniques are used to measure the X-ray arrival time, the spectral encoding based on optical gating [13] and the photon arrival and length monitor (PALM) based on THz/IR streaking [14]. For the latter the accuracy is 0.5-5 fs rms depending on the X-ray wavelength and laser jitter. The intense THz radiation is generated by the tilted pulse front method in LiNbO3 [15]. The third method with less timing accuracy employs the X-ray arrival time derived from the electron beam arrival monitor (BAM) installed at the end of the ARAMIS undulator.

X-ray Optics

The layout of the X-ray optics [16] is shown in the figure below. For pink beam a pair of bendable plane elliptical mirrors (offset mirrors) installed in the optics hutch shift the beam vertically by vertically by 20 mm. At working distance 2.5 m upstream of the endstation, a pair of bendable deflecting (8 & 12 mrad) KB-mirrors (coating Mo/B4C) provide achromatic focusing with horizontal and vertical spot size of <2 - 200 μm FWHM.
For monochromatic beam the offset mirrors are retracted. In this case the double crystal monochromator (DCM) is the first optical element in the beam. A motorized horizontal translation allows to switch between Si(111), Si(311) and Si(511) crystal pairs. The DCM has a variable offset (20 - 32 mm) to optionally operate high harmonic rejection mirrors (HHRM) with variable deflection angles in a 4-bounce scheme. The beam is kept constant at height 1420 mm as for the pink beam. A HHR of <10−4 is achieved with attenuation 100 of the fundamental. There is the option to install diamond X-ray phase retarders (XPR) in the OH hutch downstream of DCM-HHRM. Operated in Bragg/Laue transmission geometry such XPR can provide flexible linear and circular X-rays with high degree of polarization [17,18].

Experimental Hutch

Experimental Station B (ESB) is designed as a pump-probe experimental station. It combines time-resolved laser spectroscopy methods and X-ray scattering techniques to study the dynamics of cooperative interactions in crystalline materials that exhibit long-range electronic and magnetic order. The experiments will be carried out in a pump-probe mode, with an atomic resolution on the timescale of a millionth part of a billionth of a second.

X-ray pump-probe (XPP) experiment

An X-ray pump-probe (XPP) scattering experiment works as depicted in the figure below. A laser- or THz-pump-pulse excites a crystalline material, for example a CMR manganite, which exhibits long-range lattice-, charge-, orbital- and spin-order. The response of the material is measured by photon-in/photon-out scattering of a X-ray probe-pulse focussed onto the same spot. Before reaching the sample, the pump pulse bounces of a movable mirror pair (not shown) that provides a time delay between the excitation of the pump and the arrival of the probe. A 2D pixel detector records the transient, pump-induced fractional change in scattered intensity I0 (normalized to the incoming X-ray intensity I0)as a function of the time delay from the moment of pump excitation. The data are read out from the detector shot-by-shot and are written onto disk.


[1] G. Ingold, P. Beaud, et al. , SwissFEL Experimental Station B: Conceptual design Report, https://www.psi.ch/swissfel
[2] G. Ingold, J. Rittmann, P. Beaud, M. Divall, C. Erny, U. Flechsig, R. Follath, C. P. Hauri, S. Hunziker, P. Juranic, A. Mozzanica, B. Pedrini, L. Sala, L. Patthey, B. D. Patterson, and R. Abela, AIP Conf. Proc. 1741, 030039 (2016).
[3] S. L. Johnson, R. A. De Souza, U. Staub, P. Beaud, E. Möhr-Vorobeva, G. Ingold, A. Caviezel, V. Scagnoli, W. F. Schlotter, J. J. Turner, O. Krupin, W.-S. Lee, Y. D. Chuang, L. Patthey, R. G. Moore, D. Lu, M. Yi, P. S. Kirchmann, M. Trigo, P. Denes, D. Doering, Z. Hussain, Z. X. Shen, and A. T. Boothroyd, Phys. Rev. Lett. 108, 037203 (2012).
[4] T. Kubacka, J. A. Johnson, M. C. Hoffmann, C. Vicario, S. de Jong, P. Beaud, S. Grübel, S W. Huang, L. Huber, L. Patthey, Y-D. Chuang, J. J. Turner, G. L. Dakov¬ski, W-S. Lee, M. P. Minitti, W. Schlotter, R. G. Moore, C. Hauri, S. M. Koohpayeh, V. Scagnoli, G. Ingold, S. L. Johnson and U. Staub, Science 343, 1333 (2014).
[5] P. Beaud, A. Caviezel, S. O. Mariager, L. Rettig, G. Ingold, C. Dornes, S.-W. Huang, J. A. Johnson, M. Radovic, T. Huber, T. Kubacka, A. Ferrer, H. T. Lemke, M. Chollet, D. Zhu, J. Glownia, M. Sikorski, A. Robert, H. Wadati, M. Nakamura, M. Kawasaki, Y. Tokura, S. L. Johnson and U. Staub, Nature Mater. 13, 923 – 927 (2014).
[6] A. Mozzanica, A. Bergamaschi, S. Cartier, et al., J. Inst. 9, (2014).
[7] J. H. Jungmann-Smith, A. Bergamaschi, M. Brückner, et al., Rev Sci Instrum 86, 123110 (2015)
[8] B. Pedrini (private communication).
[9] T. Kampfrath, A. Sell, G. Klatt, A. Pashkin, S. Mährlein, T. Dekorsy, M. Wolf, M. Fiebig, A. Leitenstorfer, and R. Huber, Nature Photon. 5, 31 (2011).
[10] R. Mankowsky, A. Subedi, M. Först, S. Mariager, M. Chollet, H. Lemke, J. Robinson, J. Glownia, M. Minitti, A. Frano, et al., Nature (London) 516, 71 (2014).
[11] C. Ruchert, C. Vicario, and C.P. Hauri, Phys. Rev. Lett. 110, 123902 (2013).
[12] M. Nisoli, S. De Silvestri, and O. Svelto, Appl. Phys. Lett. 68, 2793 (1996).
[13] N. Hartmann,W. Helml, A. Galler, M.R. Bionta, J. Grünert, S.L. Molodtsov, K.R. Ferguson, S. Schorb, M.L. Swiggers, S. Carron, C. Bostedt, J.-C. Castagna, J. Bozek, J.M. Glownia, D.J. Kane, A.R. Fry, W.E. White, C.P. Hauri, T. Feurer, and R.N. Coffee, Nat. Photonics 8, 706 (2014).
[14] P.N. Juranic, A. Stepanov, R. Ischebeck, V. Schlott, C. Pradervand, L. Patthey, M. Radovic, I. Gorgisyan, L. Rivkin, C.P. Hauri, B. Monoszlai, R. Ivanov, P. Peier, J. Liu, T. Togashi, S. Owada, K. Ogawa, T. Katayama, M. Yabashi, and R. Abela, Opt. Expr. 22, 30004 (2014).
[15] J. Helbling, G. Almasi, I.Z. Kozma, J. Kuhl, Opt. Expr. 10, 1161 (2002).
[16] R. Follath, et al., SRI Conference Proceedings (in press).
[17] M. Suzuki, Y. Inubushi, M. Yabashi, and T. Ishikawa, J. Synchrotron Rad. 21, 466 (2014).
[18] J. Strempfer, S. Francoual, D. Reuther, D.K. Shukla, A. Skaugen, H. Schulte-Schrepping, T. Kracht and H. Franz, J. Synchrotron Rad. 20, 541 (2013).