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.

We present a general theoretical framework for multiphoton processes driven by quantum light fields, establishing a direct link between photon statistics and photoelectron observables. Our results show that the autocorrelation and cross-correlation functions, which quantify the underlying photon statistics, are directly mapped onto the resulting photoelectron spectra. Although our framework is broadly applicable, we demonstrate specifically in the example of reconstruction of attosecond beating by interference of two-photon transitions (RABBIT) the influence of the light statistical properties. In this approach, the amplitude, contrast and phase of the oscillations of the sideband signal as a function of pump-probe delay reveal the quantum nature of light. We analyze these observables across several quantum configurations, including correlated infrared and harmonic modes, as well as the uncorrelated case with non-classical harmonic statistics, thereby establishing a general framework for quantum-light RABBIT spectroscopy. We compare the analytical theory with numerical simulations for the case of classical harmonics and an infrared field in a squeezed coherent state, obtaining excellent agreement. Our results reveal how the interplay between classical and quantum correlations dictates the coherence of the photoemission process, providing a new window into the quantum-optical foundations of attosecond science.

We present the design of a VMI spectrometer optimized for attosecond spectroscopy in the 0–40 eV energy range. It is based on a compact three-electrode configuration where the lens shape, size, and material have been optimized using numerical simulations to improve the spectral resolution by a factor of ∼5 relative to the initial design [Eppink and Parker, Rev. Sci. Instrum. 68, 3477–3484 (1997)] while keeping a flat spectral response in the 10–40 eV range. The experimental performance is tested using an attosecond source based on high-order harmonic generation. A good agreement is observed between the measured and simulated spectral resolution. At low kinetic energy, the electrostatic lens remains the limiting factor, while the high energy range is mostly affected by the resolution of the camera objective.

We show that the complete photoemission dynamics in situations of electron-ion entanglement can be retrieved from photoelectron spectral measurements without information on the ion. To this end, we develop an energy-time analysis of the photoelectron's reduced density matrix based on first principles. We test and assess our approach with numerical simulations on a low dimensional model molecule in interaction with broadband composite pulses occulting the vibrational resolution. Our method is directly applicable to recent experimental schemes measuring the photoelectron reduced density matrices in atomic and molecular photoemission. Therefore, it opens a new window on the dynamics of decoherence and entanglement at the attosecond timescale.

In recent years, various methods for laser pulse post-compression have demonstrated their effectiveness. Nonlinear spectral broadening, achieved by coupling an ultrafast pulse into a gas-filled multi-pass cell (MPC), typically enables pulse compression factors exceeding 20, depending on the initial pulse duration. In this work, we report the direct post-compression of four Yb-based commercial laser systems to sub-20 fs durations, with energies up to 4 mJ and initial pulse durations ranging from 320 fs to 450 fs, using argon-filled MPCs. Each MPC was specifically designed to operate at a fixed optimal point for each laser, achieving the shortest possible pulse duration. Numerical simulations reproducing the experimental data highlight the critical influence of the driver pulse’s temporal profile on the shape of the broadened spectra. These simulations are compared with the experimental results, demonstrating strong agreement.

We report here on the experimental pulse duration compression down to sub-20fs of up to 2mJ, 330fs pulses of an 80W Ytterbium laser, using argon-filled multi-pass-cell reproduced by numerical calculations stressing the role of the driver pulse profile.

In the last years, different methods of laser pulse post-compression have proven their efficiency. Nonlinear spectral broadening achieved when coupling an ultrafast pulse in a gas-filled multi-pass-cell (MPC) provides common pulse compression factors of 10 to 20, depending on the initial pulse duration. We report here on the compression of up to 2 mJ, 330 fs pulses of an Ytterbium (Yb) based laser down to sub-20 fs (compression factor of 17), using argon-filled MPCs, at the limit of temporal pulse breakup. Numerical calculations reproducing the experiment data, and demonstrating the importance of the driver pulse profile on the shape of the broadened spectra, are discussed.

Chapter 3 presents an introduction and sections on: quantum many-body systems and emergent phenomena; the search for new materials; manipulating photons and atoms: photonics and nanophysics; extreme light; systems with numerous degrees of freedom;

Le développement spectaculaire des lasers de puissance ces trente dernières années a ouvert de nouveaux champs d’études : la science attoseconde d’une part, l’optique relativiste d’autre part. Nous illustrons les nouvelles perspectives ouvertes dans divers domaines de la physique, la chimie, la médecine ou la science des matériaux à partir d’études effectuées sur les plateformes ATTOLab et UHI100 du Laboratoire Interactions, Dynamiques et Lasers (LIDYL) du CEA Paris-Saclay.

Strong-field ionization of molecules releases electrons which can be accelerated and driven back to recombine with their parent ion, emitting high-order harmonics. This ionization also initiates attosecond electronic and vibrational dynamics in the ion, evolving during the electron travel in the continuum. Revealing this subcycle dynamics from the emitted radiation usually requires advanced theoretical modeling. We show that this can be avoided by resolving the emission from two families of electronic quantum paths in the generation process. The corresponding electrons have the same kinetic energy, and thus the same structural sensitivity, but differ by the travel time between ionization and recombination-the pump-probe delay in this attosecond self-probing scheme. We measure the harmonic amplitude and phase in aligned CO2 and N2 molecules and observe a strong influence of laser-induced dynamics on two characteristic spectroscopic features: a shape resonance and multichannel interference. This quantum-path resolved spectroscopy thus opens wide prospects for the investigation of ultrafast ionic dynamics, such as charge migration.

The 2023 Nobel Prize in Physics has been awarded to Anne L’Huillier, Pierre Agostini and Ferenc Krausz “for experimental methods that generate attosecond pulses of light for the study of electron dynamics in matter”. In this article, we contextualize their seminal works and their central roles that led to the emergence of a global ultrafast community exploring the frontiers of electron dynamics in dilute and condensed matter.

We present the commissioning of the FAB10 beamline (Femtosecond to Attosecond Beamline at 10 kHz repetition rate) that has been developped and operated in the last few years at the ATTOLab facility of Paris-Saclay University. Based on the high harmonic generation process, the beamline is dedicated to investigations of ultrafast dynamics in a broad variety of systems ranging from gas phase to condensed matter in pump-probe arrangements. Its design and operation has been strongly influenced by both the laser and the large scale instruments communities, which makes it unique in several aspects. In particular, it is possible to tune the extreme ultraviolet (XUV, 10–100 eV) bandwidth from 0.2 to 20 eV – with corresponding pulse duration from 30 to 0.3 femtoseconds (fs) – thanks to an original and fully automated XUV spectral filter with three operation modes. After a general overview of the beamline features, each of those operation modes is described, characterized and illustrated with commissioning experiments.

Quantum coherence plays a fundamental role in the study and control of ultrafast dynamics in matter. In the case of photoionization, entanglement of the photoelectron with the ion is a well known source of decoherence when only one of the particles is measured. Here we investigate decoherence due to entanglement of the radial and angular degrees of freedom of the photoelectron. We study two-photon ionization via the 2s2p autoionizing state in He using high spectral resolution photoelectron interferometry. Combining experiment and theory, we show that the strong dipole coupling of the 2s2p and 2p$^2$ states results in the entanglement of the angular and radial degrees of freedom. This translates, in angle integrated measurements, into a dynamic loss of coherence during autoionization.

Imaging in real time the complete dynamics of a process as fundamental as photoemission has long been out of reach because of the difficulty of combining attosecond temporal resolution with fine spectral and angular resolutions. Here, we achieve full decoding of the intricate angle-dependent dynamics of a photoemission process in helium, spectrally and anisotropically structured by two-photon transitions through intermediate bound states. Using spectrally and angularly resolved attosecond electron interferometry, we characterize the complex-valued transition probability amplitude toward the photoelectron quantum state. This allows reconstructing in space, time, and energy the complete formation of the photoionized wave packet.

We photoionize nitrogen molecules with a train of extreme ultraviolet attosecond pulses together with a weak infrared field. We measure the phase of the two-color two-photon ionization transition (molecular phase) for different states of the ion. We observe a $0.9\ensuremath{\pi}$ shift for the electrons produced in the ionization channels leading to the $X\text{ }{^{2}\ensuremath{\Sigma}}_{g}^{+}$, ${v}^{\ensuremath{'}}=1$, and ${v}^{\ensuremath{'}}=2$ states. We relate this phase shift to the presence of a complex resonance in the continuum. By providing both a high spectral and temporal resolution, this general approach gives access to the evolution of extremely short-lived states, which is often not accessible otherwise.

We study helium two-photon ionization using attosecond electron interferometry in a velocity-map imaging spectrometer. The complete dynamics of the photoemission process is then reconstructed in space and time.

Generating high-energy few-cycle pulses is key in the study of light-matter interaction in the regime of high field physics. Attosecond science possess the necessary time resolution to study the underlying fundamental processes but requires repetitions rates on the order the kilohertz and stabilization of the Carrier-Envelope Phase. We present here a post-compression stage delivering 3.8fs pulses with 2.5mJ coupled to a Ti: Sa based 1 kHz TW-class laser which can deliver 17.8fs pulses with 350mrad shot to shot CEP noise. This is the first step towards high-energy few-cycle post-compression of the FAB laser at ATTOLAB-Orme.

Using momentum-resolved electron interferometry, we image helium two- photon ionization through intermediate bound states. This allows reconstructing in space and time the complete formation of the photoionized wavepacket.

Using a spectrally resolved electron interferometry technique, we measure photoionization time delays between the $3s$ and $3p$ subshells of argon over a large 34-eV energy range covering the Cooper minima in both subshells. The observed strong variations of the $3s-3p$ delay difference, including a sign change, are well reproduced by theoretical calculations using the Two-Photon Two-Color Random Phase Approximation with Exchange. Strong shake-up channels lead to photoelectrons spectrally overlapping with those emitted from the $3s$ subshell. These channels need to be included in our analysis to reproduce the experimental data. Our measurements provide a stringent test for multielectronic theoretical models aiming at an accurate description of inter-channel correlation.