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Proposal for FEMTO Diffraction Endstation at SLS for Femtosecond Laser-X-Ray Pump-Probe Experiments at low Temperatures

Applicant Ingold Gerhard
Number 128750
Funding scheme R'EQUIP
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Condensed Matter Physics
Start/End 01.12.2010 - 30.11.2011
Approved amount 342'000.00
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Keywords (8)

Femtosecond x-ray diffraction; Ultrafast dynamics in solids; Strongly correlated electron systems; correlected electron systems; pump-probe; experiments; UHV cryo diffraction endstation; SwissFEL free electron laser

Lay Summary (English)

Lead
Lay summary
The new endstation under construction at the FEMTO source at the SLS will allow to study femtosecond (fs) dynamics in strongly correlated electron systems at low temperatures by means of laser-pump/x-ray-probe (XPP) resonant and non-resonant (grazing incidence) x-ray diffraction. These systems show novel electronic behaviour (such as metal-insulator transition, colossal magnetoresistance, multiferroicity, high-Tc supercon-ductivity) caused by the interplay of charge-, orbital-, spin- and atomicorder. A strong pulse of light can disturb this order and lead to a persistent new phase with a different complex type of order. The study of the micro-scopic origin of such cooperative ordered phases at the fs time scale is anew research field which will also be pursued at the new free electron la-ser facilities LCLS (Stanford), EU-XFEL (Hamburg) and SwissFEL (Villigen).The new endstation will be realized in two steps, phase-I and phase-II. It consists of the multilayer (ML) chamber (monochromator), the chamber for the KB-optics (refocusing optics), and the experimental station. The present (January 2011) status is as follows:Experiments: In 2010 we have successfully performed 3 experiments. At FEMTO the dynamics of a structural order parameter in TiSe2 in the charge density wave phase has been measured. In a second experiment we studied the lattice and magnetic dynamics of a laser induced magnetic phase transition in FeRh. And finally we performed a first successful ex-periment at the SXR endstation at the LCLS by directly observing the fsmagnetic order dynamics of a multiferroic phase transition in CuO. Mean- while we have submitted new proposals for experiments at the SXR and the XPP endstation at the LCLS (for the latter we propose to use as experi- mental station the HV hexapod-goniometer of phase-I).Phase-I: After having received the custom made hexapod sample manipu-lator, it has been integrated into the control system and used for laborato-ry work to test critical design concepts. The detailed engineering design ofthe ML-chamber has been finished and manufacturing has started. TheKB-chamber is finished and laboratory tests prior to installation are in pro-gress. The commissioning of the new phase-I endstation will start in the second half of 2011.Phase-II: The conceptual engineering design of the experimental station(UHV cryo-diffractometer) has been finished. After internal review we willproceed with the detailed engineering design. After 3-4 years of operationat FEMTO, we plan to install this experimental station at SwissFEL in 2016to start first experiments.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Scientific events



Self-organised

Title Date Place
Ultrafast Dynamics in Strongly Correlated Systems 04.06.2011 Zürich

Associated projects

Number Title Start Funding scheme
124496 Femtosecond optical and x-ray studies on ultrafast dynamics in manganites associated with phase transitions 01.04.2010 Project funding (Div. I-III)

Abstract

The development of a compact UHV diffractometer station for hard X-rays is proposed. It will be installed at the microXAS beamline of the Swiss Light Source at the Paul Scherrer Institut (PSI). At this beamline a femtosecond laser slicing source, FEMTO, is installed. FEMTO is currently the only tunable X-ray undulator source delivering temporally and spatially stable X-ray pulses in the range 5 - 12 keV to perform laser-X-ray pump-probe (XPP) experiments with timeresolution 200 fs. Currently 40% of the beamtime at the microXAS beamline is devoted to time-resolved experiments.This will allow temporary installation of the new diffractometer at the LCLS, the first free electron laser (XFEL) in the hard X-ray regime that very recently demonstrated lasing at 8 keV. The LCLS-XFEL experiments will extend our research program started at FEMTO by exploiting resonant scattering, the much higher flux, and eventually a higher time resolution of ultimately 10 fs. When the PSI-XFEL, currently in its design stage, has first light in the beginning of 2016, this type of experiment will be pursued at the hard X-ray XFEL beamline at PSI.At FEMTO two classes of experiments are performed: femtosecond grazing incidence X-ray diffraction on crystalline solids, and femtosecond absorption spectroscopy in solvated molecular systems. Both the solid state experiments and the femtochemistry experiments will profit from the enhanced flux (x 3) due to the installation of the new refocussing optics in conjunction with the proposed new diffraction station. At present a simple non-UHV chamber is available for XPP diffraction experiments at sample temperatures above 170 K. The temperature control for this chamber is limited by the vacuum that can be reached.Femtosecond XPP diffraction combines real time measurements on a short time scale with atomic resolution to capture the transient rearrangement of atoms. A significant challenge in condensed matter, and in particular in strongly correlated systems, is understanding the dynamic interplay between valence charge distribution, orbital order, spin orbit, and subtle distortions of the atomic lattice that give rise to complex phase diagrams. The most relevant energy scale is the temperature in the range 20 - 250 K at which ordering occurs in complex systems. Typical time scales are 100 fs for the vibrational atomic motion and 10 fs for the electron-electron (e-e) scattering time. The extended temperature range of the new station in combination with femtosecond Bragg diffraction will allow for a wide range of interesting compounds, including complex and magnetic materials, the separation of correlated electronic and structural phenomena in the time domain and the observation of the underlying correlations in real space as they develop. At FEMTO we can study the stimulated structural changes on the fundamental time scale of fluctuations in the vicinity of the transition point during a phase transition or ordering process when the sample is near the critical temperature. Because conventional Bragg diffraction lacks sensitivity to electronic structural dynamics, we propose to develop time-resolved pump-probe resonant X-ray diffraction (RXD) by combining XPP and RXD techniques. Preliminary XPP-RXD measurements can be started at FEMTO, but the higher flux and better time resolution provided by XFELs will ultimately be needed. The XPP-RXD experiments in the hard X-ray regime will be complementaryto the time resolved resonant scattering experiments we pursuein the soft X-ray range.
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