Focus

Introduction

Following the technological progress in laser science, strong-field physics and attosecond science have attracted a lot of attention as means to manipulate and probe the electronic structure of matter at the scale of the atom and molecule. Strong-field physics is interested in the interaction processes between a very short and intense pulse and atoms and molecules, as illustrated in the figure above. Attosecond science (1 attosecond = 10-18 seconds), on its side, focuses one ultra-short process -- sub-femtosecond (10-15 s) -- and the by-products associated with the laser-matter interaction.  Although they are strongly linked together, the stakes raised by these fields of research can be globally sorted into two perspectives. The first one focuses on the development of new laser sources with high performance, including a large engineering component. The second one, more fundamental is interested in the study, understanding and control of matter at the scale of the electron dynamics, resolved in time and space, in atoms and molecules. Quite naturally, the performance of these laser sources is conditioned to the control of the electron dynamics. In return, these new high performance laser sources can be used to probe matter with always more precision and resolution.

Figure description

Scheme of principle of experiments in strong-field physics and attosecond science: A very short and strong laser pulse is focused onto a gas of atoms or molecules (main frame). Associated measures (dotted frame) can be interested in different scales of the laser-matter interaction. ① At the microscopic scale, the laser field can lead, for instance, to the ionization of one or several electrons of the target. Those charged particles keep interacting with the field and are further accelerated, leading to the emission of an electromagnetic radiation. ② At the macroscopic scale, in favorable conditions, the radiation from each emitting particle adds up coherently, leading to a laser effect. Each scale raises several different stakes and scientific interests, as indicated in the right part of the figure.

Context

The intrinsic coherence of the electron dynamics induced by the interaction with the laser is one of the key ingredients of the success of strong-field physics and attosecond science in that it imprints structural and dynamical properties of matter onto the by-products of the interaction with the laser. Without being exhaustive, the study of those by-products is interested in the measure of photoelectrons -- as by-products of ionization -- ions and fragments -- e.g., as by-products of molecular rearrangement associated with ionization process -- at the microscopic scale and in high-harmonic generation (HHG) -- at the macroscopic scale. Fundamentally, the range of intensities typically considered is located in a range where Coulomb and external laser interactions are comparable, putting strong-field physics and attosecond science in a (highly) nonlinear and non-perturbative regime. On the theoretical perspective, the electron dynamics at the microscopic scale is most often described with the time-dependent Schrödinger equation (TDSE), i.e., within quantum frameworks although classical and semi-classical models have been developed across the years. In this general framework, my research has been introducing and applying modern tools of nonlinear dynamics, within the Hamiltonian formalism, to study, model and predict the properties of matter at the electron scale, under the influence of the external laser field, using classical, semi-classical and quantum models.

Focus pages