SIMES Seminar: Laura Foglia

Date(s) - Apr 6 2018
1:00 PM - 2:00 PM

Shasta Room, Bldg. 40, Room 361


Probing fundamental excitations at the nanoscale: XUV transient grating and beyond

Laura Foglia

Elettra Sincrotrone Trieste S.c.P.A. ., S.S. 14 km 163,5 in Area Science Park, Basovizza, I-34012, ITALY.

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.

L. Foglia et al., Four-wave-mixing experiments and beyond: The TIMER/mini-TIMER setups at FERMI, Proceedings of SPIE, 10237, 102370C (2017).

P. Rebernik Ribič et al., Extreme-Ultraviolet Vortices from a Free-Electron Laser, PRX, 7, 031036 (2017).

A. Simoncig et al., Generation of coherent magnons in NiO stimulated by XUV pulses from a seeded free-electron laser, Phys. Rev. Materials, 1, 073802 (2017).

F. Capotondi, L. Foglia et al., Ultrafast EUV autocorrelation measurements using transient gratings, J. Synchrotron Rad., 25, 1 (2018).

R.K. Lam et al., Soft X-ray Second Harmonic Generation as an Interfacial Probe, PRL 120, 023901 (2018)


Short CV

Laura obtained her bachelor in Physic at the University of Genova in 2009. She completed her Physik Diplom in 2011 on the metal to insulator transition of VO2 in the group of Julia Stähler at the Fritz Haber Institute in Berlin directed by Martin Wolf. There she finished her PhD work on exciton and charge dynamics at a hybrid organic/inorganic interfaces in 2015. Since May 2016, Laura is working as a postdoc at the Elastic and Inelastic Scattering (EIS) beamlines of the Italian free electron laser FERMI and extents nonlinear optical techniques to sub-optical wavelengths at the TIMEX, TIMER and DiProI endstations.