Conference Agenda

In my presentation, I will discuss the innovative prospectives presented by Free Electron Lasers (FELs) for attosecond science. Specifically, it will elucidate how attosecond metrology and spectroscopy can be implemented at seeded FELs by substituting the necessity for synchronization between the attosecond pulse train and the infrared laser pulse with a correlated examination of the single-shot photoelectron spectra.

Ultrashort light pulses can be used to manipulate electronic and optical properties of solids at extreme temporal scales, paving the way to the study of ultrafast electron dynamics. In recent years, attosecond-based spectroscopic techniques have proved to be an instrumental tool in such studies. To this end, we investigated the effects of crystal orientation on ultrafast photoinjection dynamics in germanium using attosecond transient reflectance spectroscopy (ATRS) aided by time-dependent density functional theory (TD-DFT) calculations. Our results show that ATRS is sensitive to subtle changes in the transient reflectance due to crystal orientation, although carrier photoinjection in germanium is qualitatively robust against crystal rotation, displaying similar photoinjection processes and timings at two different crystal angles.

High-order harmonic spectroscopy is a robust method for probing electron dynamics under the influence of a driving field, capturing phenomena as brief as attoseconds. It relies on the extreme non-linear process of high-harmonic generation (HHG), where intense laser pulses are directed at a material, causing it to emit high-energy photons in harmonics of the laser frequency. In this contribution we explore the possibility to generate high-order harmonics from low-dimensional crystalline solids driven under grazing incidence. We demonstrate that, in this unconventional geometry, the electron wavefunction is ejected from the solid and, subsequently, redirected to it to generate harmonics. Most appealingly, we show that the crystal’s periodicity imprinted in the electron’s wavefunction introduces a revival dynamics closely connected with the matter temporal Talbot effect. These Talbot oscillations are ultrafast (< femtosecond) and leave a distinct signature in the high-frequency harmonic spectrum, in the form of structures extending beyond the main spectral cutoff.

We explore via numerical modeling the generation of very short photon wavelengths in hollow core waveguides (HCW) filled with He gas at high pressures. Propagation of femtosecond driving pulses is first solved using a split-step method and tested against other methods. The propagation along the HCW reveals mode beating seen in quasi-periodic oscillations of the field intensity and phase which in turn will determine the single atom response to the field.

We explore both cylindrical and conical HCW in which the guide diameter varies along the propagation direction. This second configuration generates very high harmonic orders in a regime of quasi-phase matching. We found three spectral ranges which show amplification, at 3.5, 7.6, and 11-13 nm, which are of great interest given their practical applications in spectroscopy, XUV metrology and photolithography.

Ultrafast charge transfer processes in organic materials which occur in organic materials are fundamental for advancing solar energy conversion technologies. Understanding these phenomena on a short time scale induced by visible and ultraviolet (UV) light is crucial for future control and engineering of these molecules. Here, we present a novel attosecond beamline featuring Resonant Dispersive Wave emission for generating sub-3 fs tunable pump pulses in the UV region and High Harmonic Generation (HHG) in a semi-infinite gas cell for isolated attosecond pulse generation in the Extreme ultraviolet range.