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Pierre Agostini

Publications and source records attributed to Pierre Agostini.

5 recordsLinked to original sources
arXiv2026

Roadmap on Attosecond Science

Twenty-five years have passed since the first experimental demonstration of attosecond pulses, marking the advent of our ability to resolve and control electron motion in real time. What began as a technological breakthrough - generating the shortest flashes ever produced - has evolved into a powerful approach for probing and steering electronic dynamics in atoms, molecules, and solids. This roadmap, authored by leading experts in the field, surveys the recent rapid progress in the generation and characterization of attosecond pulses, emerging attosecond measurement and control techniques, and their expanding range of applications. It reviews current and future developments in attosecond light sources, including novel laser technologies, waveform synthesizers, new schemes for high-order harmonic generation, attosecond pulse generation at free-electron lasers, and structured light. Advances in attosecond measurement methodologies are also discussed, encompassing all-attosecond pump-probe spectroscopy, attosecond four-wave mixing, attosecond microscopy, spectroscopy with light transients, and attosecond interferometry. Furthermore, the roadmap addresses applications of attosecond spectroscopy to reveal electron dynamics in molecules and condensed matter systems from both theoretical and experimental perspectives, and highlights emerging directions at the interface with quantum optics and quantum entanglement. Overall, this work aims to serve as a comprehensive resource for navigating the evolving landscape of attosecond science.

physics.optics↗
arXiv2026

Disentangling High Harmonic Generation from Surface and Bulk States of a Topological Insulator

The discovery of topological phases has introduced a new dimension to materials science. Three-dimensional (3D) topological insulators (TIs) are a remarkable class of matter that is insulating in the bulk while hosting conductive topological surface states (TSSs) with unique charge and spin properties. High-order harmonic generation (HHG) has emerged as a powerful tool to probe condensed matter systems by providing insights into their electronic structure and dynamic behavior. Here, we investigate HHG in the prototype 3D-TI Bi$_2$Se$_3$. We demonstrate that the contributions of bulk and surface states to the harmonic emission can be controlled by tuning the thickness of thin film samples. An ultrathin (6 nm) film substantially enhances HHG from the surface states, while the bulk states dominate HHG in a thicker (50 nm) film. By applying a quasi-static terahertz perturbing field, we disentangle the bulk and surface responses and reveal the significant impact of the surface states' shift vector and Berry curvature on HHG. Our study provides effective methods for isolating the optical responses of TSSs from those of the bulk, which opens the door to resolving an ongoing debate regarding whether it is possible to reliably extract topological signatures in HHG.

cond-mat.mes-hall↗
arXiv2025

Intense THz s-SNOM for nonlinearity engineering in nanoscale

Terahertz (THz) nonlinear optics offer powerful tools to investigate and manipulate electronic dynamics in condensed matter. Confining high-peak-power THz pulses within near field can effectively generates extremely localized electromagnetic fields in spatio-temporal, enabling to precisely explore and control carrier transient dynamics from THz nonlinearity perspective. However, the combination of the high peak power THz pulses and the near-field optic techniques remains challenging due to the incompatibility between low repetition THz pulses and typical near-field demodulation schemes. Here, we construct high peak power THz scattering scanning near-field microscopy (THz s-SNOM) by combining THz pulses emitted from two-color femtosecond laser filaments with a tapping mode atomic force microscopy (AFM) and explore efficient THz third harmonics generation (THG) from the Cd3As2 film in nanoscale. The power-law dependence of the THz harmonics and theoretical calculation reveals a convincing third harmonic generation that is attributed to the nonequilibrium intraband dynamics driven by the strong THz pulses. Especially, the nanoscopic near-field THz third harmonic imaging with resolution of 200 nm ({\lambda}/3000) of 3D Dirac semimetal are demonstrated. The high peak power THz s-SNOM can provide a great platform for exploring and manipulating the nonlinear physics, carrier dynamics and quantum coherent phenomena driven by the localized THz field with nanoscale resolution, thereby guiding the development of the integrated high-performance nonlinear photonic devices.

physics.optics↗