In-situ observation of the formation of laser-induced periodic surface structures with extreme spatial and temporal resolution

TL;DR

This paper reports on in-situ experiments using free electron lasers to observe laser-induced surface structures forming at nanometer to micron scales with sub-picosecond temporal resolution, revealing dynamic structural changes under extreme conditions.

Contribution

It demonstrates the use of advanced FEL-based scattering techniques to directly observe surface structure formation during ultrashort laser irradiation at unprecedented spatial and temporal resolutions.

Findings

Resolved surface structure formation at nanometer to micron scales.

Captured dynamics from picoseconds to nanoseconds with sub-picosecond resolution.

Provided insights into non-equilibrium structural changes under intense laser pulses.

Abstract

Irradiation of solid surfaces with intense ultrashort laser pulses represents a unique way of depositing energy into materials. It allows to realize states of extreme electronic excitation and/or very high temperature and pressure, and to drive materials close to and beyond fundamental stability limits. As a consequence, structural changes and phase transitions often occur along unusual pathways and under strongly non-equilibrium conditions. Due to the inherent multiscale nature - both temporally and spatially - of these irreversible processes their direct experimental observation requires techniques that combine high temporal resolution with the appropriate spatial resolution and the capability to obtain good quality data on a single pulse/event basis. In this respect fourth generation light sources, namely short wavelength, short pulse free electron lasers (FELs) are offering new and fascinating possibilities. As an example, this chapter will discuss the results of scattering experiments carried at the FLASH free electron laser at DESY (Hamburg, Germany), which allowed us to resolve laser-induced structure formation at surfaces on the nanometer to sub-micron length scale and in temporal regimes ranging from picoseconds to several nanoseconds with sub-picosecond resolution.