Functional processes transform between different material properties, occur on ultrafast timescale, and out of equilibrium. Such can be particularly complex in condensed matter, as the interactions depend on processes on multiple time and length scales. Free Electron Lasers (FELs) provide here new experimental insight with ultrafast X-ray probes for electronic and atomic structures. Science...
Titanium Pentaoxide nanocrystals exhibit two stable phases at ambient temperature, a more conductive $\lambda$ phase and a more insulating one ($\beta$) stabilized by pressure. The $\beta\rightarrow\lambda$ transition can be induced by short pulse irradiation. Following preliminary experiments at ID9 (ESRF) beamline, we have performed powder diffraction in Bernina to map the structural...
Different cases are presented on how ultrafast x-ray pulses can be used to study ultrafast dynamics in correlated electron systems. It is shown how an optical excitation can drive an electronic transition and its perspective to drive it by direct phonon excitation. In addition, it is shown how we can increase a structural order parameter with an electronic excitation in a simple perovskite and...
Identifying the degrees of freedom that lead to the emergence of superconductivity in iron-based materials remains the subject of active research. Amongst spin-driven scenarios, it has also been suggested that electron-electron correlations enhance the electron-phonon coupling in iron chalcogenides and related pnictides, but direct experimental verification has been lacking. We show that the...
I will present the results obtained within my PhD. The main goal was to study the femtosecond photo-switching dynamic in bistable molecular materials, using optical and x-ray ultrafast spectroscopies. A part of this work focuses on the study of Prussian Blue Analogues (CoFe), which are prototype bistable metallic cubic crystals. Among the great interests of these systems are their bistable...
Tuneable THz radiation could be used to selectively excite low-frequency substrate-molecule modes relevant to the catalytic activity. Probing of such motion requires a technique with high structural sensitivity and temporal resolution, such as photoelectron diffraction. Metallic catalyst surfaces strongly modify the electric field of the pump pulse due to dielectric screening. Here we present...
Spin currents generated by ultrafast laser excitation of a magnetic thin film was predicted theoretically [1] and found in magneto-optical measurements using fs-pulsed VUV radiation [2]. Here we show fs time-resolved x-ray magnetic circular dichroism measurements performed at LCLS SXR on similar Ni/Ru/Fe multilayers that were used before [2]. Contrary than in [2], we find in our time- and...
The soft x-ray line of SwissFEL, Athos, is currently under construction. This new FEL line will cover the photon energy range from 250 eV to 1900 eV. Athos will include several innovations allowing more complex modes of operation as the standard SASE FEL mode. Small magnetic chicanes between every undulator segments will allow to delay or shift electron bunches in order to better control FEL...
Resonant Inelastic X-ray Scattering (RIXS) is a powerful momentum-resolved probe of excitations involving lattice, charge, orbital and spin degrees of freedom for a diversity of materials. With the development of intense pulsed x-ray sources from free electron lasers, it is very attractive to extend this advanced spectroscopy into the time-domain.
After introducing the RIXS technique, we will...
Structure determination is an important activity spanning across disciplines such biology, chemistry and physics. X-ray diffraction is among the powerful techniques used for structure refinements. The emergence of hard x-ray free electron laser facilities including the SwissFEL has open entirely new opportunities. This talk will discuss how synchronization for free electron laser pulses with...
Extending the methodologies of nonlinear optics to the X-ray regime is a promising and exciting avenue in the light of the recent development of X-ray free electron lasers. For the first time, space, time, and energy resolved XUV-transient grating experiments on S3N4 membranes recorded around the Si L2,3-edge have been realized. The observed signal decays have been assigned to ultrafast charge...
The hard X-ray branch of SwissFEL, Aramis, has successfully completed initial pilot experiments while developments continue of the soft X-ray branch, Athos.
The current status of the commissioned diagnostics measuring temporal, spectral and intensity properties of the FEL pulses are presented.
Plans for photon diagnostics for Athos and also describe. By presenting these details now, it is...
The Accelerator on a Chip International Program (ACHIP) is an international collaboration, funded by the Gordon and Betty Moore Foundation, with the goal to demonstrate that laser-driven accelerator on a chip can be integrated to fully build an accelerator based on dielectric structures. PSI will provide access to the high brightness electron beam of SwissFEL to test structures, approaches and...
We will report on the first pilot experiments at the Alvra experimental station of SwissFEL employing X-ray spectroscopy methods in the tender X-ray regime. The experiments allowed testing the main instrumental components of the beamline with application to pump-probe X-ray emission spectroscopy on applied (charge transfer in OLED and TiO2 systems) and fundamental research (UV...
With the advent of X-ray Free Electron Lasers, it is now possible to combine novel experimental strategies, based on ultrafast element-selective core-level spectroscopies and scattering techniques. This unique capability can be harnessed to study the interplay of electronic and structural degrees of freedom in several photo-excited systems. Here, I will provide examples how this approach can...
Myoglobin(Mb) is a small protein consisting of a single polypeptide chain and a heme as its active center. The photodissociation of the NO ligand from low spin MbNO leads its recombination to the high spin, domed and unligated porphyrin, which occurs over multiple timescales (from sub-ps to 100s ps) through an intermediate state that is presumed to be a high spin domed ligated form. We will...
Free-Electron Lasers (FELs) are capable of producing intense and ultrashort X-ray pulses, which enable femtosecond time-resolved diffractive imaging experiments. This allows to initiate chemical reactions in molecules using an optical pump pulse and probing the induced changes in the nuclear structure by X-ray scattering using a delayed FEL pulse. Here, results on the strong-field induced...
The novel x-ray free-electron laser sources, including the upcoming SwissFEL, offer new opportunities for the investigation of ultrafast phenomena in the chemical, materials, and biological sciences. The high number of photons (10^12) per pulse in combination with femtosecond pulse length allows new approaches in x-ray based imaging and spectroscopy, including single-shot imaging of single...
