AVS 65th International Symposium & Exhibition
    Novel Trends in Synchrotron and FEL-Based Analysis Focus Topic Thursday Sessions
       Session SA+MI-ThM

Invited Paper SA+MI-ThM5
XUV-transient Grating: Probing Fundamental Excitations at the Nanoscale

Thursday, October 25, 2018, 9:20 am, Room 202A

Session: Ultra-fast Dynamics for Magnetic and Quantum Systems
Presenter: Laura Foglia, Elettra-Sincrotrone Trieste, Italy
Authors: L. Foglia, Elettra-Sincrotrone Trieste, Italy
F. Capotondi, Elettra-Sincrotrone Trieste, Italy
R. Mincigrucci, Elettra-Sincrotrone Trieste, Italy
D. Naumenko, Elettra-Sincrotrone Trieste, Italy
E. Pedersoli, Elettra-Sincrotrone Trieste, Italy
A. Simoncig, Elettra-Sincrotrone Trieste, Italy
G. Kurdi, Elettra-Sincrotrone Trieste, Italy
M. Manfredda, Elettra-Sincrotrone Trieste, Italy
L. Raimondi, Elettra-Sincrotrone Trieste, Italy
N. Mahne, IOM-CNR, Italy
M. Zangrando, Elettra-Sincrotrone Trieste, Italy
C. Masciovecchio, Elettra-Sincrotrone Trieste, Italy
F. Bencivenga, Elettra-Sincrotrone Trieste, Italy
Correspondent: Click to Email
Nonlinear optical spectroscopies take advantage of multiple light-matter interactions via the Nth-order susceptibilities, to disentangle and selectively access the many interacting degrees of freedom that characterize complex systems. Indeed, the control on photon parameters (frequency, arrival time, polarization, etc.) for each field independently gives rise to a manifold of experimental techniques that allow to monitor, on ultrafast timescales, structural changes, spin and electron dynamics, collective phenomena as well as to selectively probe correlations among different excitations. Among the nonlinear processes, third order, or four-wave-mixing (FWM), interactions occur in all materials independently of their symmetry, and are thus the most widely used in applications. While nowadays these techniques are well established at optical wavelengths, their birth required the invention of the laser. Similarly, their extension to sub-optical wavelengths (XUV and X-ray), envisioned theoretically more than a decade ago, had to wait until the recent development of free electron lasers (FELs). XUV-FWM will allow exploiting core-hole resonances to address correlations among low-energy excitations and core states as well as monitoring charge and energy transfer processes. Additionally, it will extend the accessible wavevector range to the mesoscopic regime (0.1-1 nm−1), which is fundamental to investigate, e.g., lattice dynamics in nanostructures and disordered systems as well as transport phenomena at the nanoscale.

Here I report on the demonstration of XUV four-wave-mixing response in a transient grating (TG) approach, exploiting the unique properties of the seeded FEL source FERMI and of two dedicated setups: TIMER and mini-TIMER. All-XUV TG data allowed us to determine the phonon and thermal dynamics of several semiconductors in an uncharted length-scale range, extending down to ≈20 nm. The results are compared with those of XUV pump/optical probe TG, evidencing different couplings to the electronic subsystem.

Additionally, I present the first evidence of FWM processes stimulated by FEL pulses at different wavelengths, obtained exploiting the multi-color capabilities of FERMI and will discuss the foreseen implementation of second order wave-mixing techniques for the chemical and interface specific probing of electronic processes.