Surface charges play a fundamental role in physics and chemistry, in particular in shaping the catalytic properties of nanomaterials. However, tracking nanoscale surface charge dynamics remains challenging due to the involved length and time scales. Here, we demonstrate time-resolved access to the nanoscale charge dynamics on dielectric nanoparticles using reaction nanoscopy. We present a four-dimensional visualization of the spatiotemporal evolution of the charge density on individual SiO 2 nanoparticles under strong-field irradiation with femtosecond-nanometer resolution. The initially localized surface charges exhibit a biexponential redistribution over time. Our findings reveal the influence of surface charges on surface molecular bonding through quantum dynamical simulations. We performed semi-classical simulations to uncover the roles of diffusion and charge loss in the surface charge redistribution process. Understanding nanoscale surface charge dynamics and its influence on chemical bonding on a single-nanoparticle level unlocks an increased ability to address global needs in renewable energy and advanced health care.

Abstract Tracing the dynamical behavior of light-induced surface charges on nanostructures is pivotal for elucidating the fundamental processes governing catalysis and light-nanomaterial interactions. Extension to nanoscale surface charge dynamics, however, remained challenging due to the involved length and time scales. Here, we demonstrate direct observation of surface charge dynamics on dielectric nanoparticles under strong-field irradiation using time-resolved reaction nanoscopy. Our technique offers four-dimensional visualization of the spatiotemporal evolution of localized charges on spherical SiO2 nanoparticles, providing unprecedented resolution at the femtosecond-nanometer scale and single-nanoparticle level. Through semi-classical simulations, we reveal the distinct roles and characteristic timescales of diffusion and decay processes driving surface charge relaxation on SiO2 nanoparticles. Quantum dynamical simulations reveal bond-weakening in adsorbate molecules at the nanosurface, attributed to the presence of the surface charges. Unveiling nanoscale charge dynamics and their impact on surface molecular bonding highlights the potential for designing nanomaterials with tailored functionalities, propelling atomic-scale technologies and catalysis to new frontiers.

In recent years, the stacking and twisting of atom-thin structures with matching crystal symmetry has provided a unique way to create new superlattice structures in which new properties emerge1,2. In parallel, control over the temporal characteristics of strong light fields has allowed researchers to manipulate coherent electron transport in such atom-thin structures on sublaser-cycle timescales3,4. Here we demonstrate a tailored light-wave-driven analogue to twisted layer stacking. Tailoring the spatial symmetry of the light waveform to that of the lattice of a hexagonal boron nitride monolayer and then twisting this waveform result in optical control of time-reversal symmetry breaking5 and the realization of the topological Haldane model6 in a laser-dressed two-dimensional insulating crystal. Further, the parameters of the effective Haldane-type Hamiltonian can be controlled by rotating the light waveform, thus enabling ultrafast switching between band structure configurations and allowing unprecedented control over the magnitude, location and curvature of the bandgap. This results in an asymmetric population between complementary quantum valleys that leads to a measurable valley Hall current7, which can be detected by optical harmonic polarimetry. The universality and robustness of our scheme paves the way to valley-selective bandgap engineering on the fly and unlocks the possibility of creating few-femtosecond switches with quantum degrees of freedom.

Accurate estimation of the duration of soft-x-ray pulses from high-harmonic generation (HHG) remains challenging given their higher photon energies and broad spectral bandwidth. The carrier-envelope-phase (CEP) dependence of generated soft-x-ray spectra is indicative of attosecond pulse generation, but advanced simulations are needed to infer the pulse duration from such data. Here, we employ macroscopic propagation simulations to reproduce experimental polarization-gated CEP-dependent soft-x-ray spectra. The simulations indicate chirped pulses, which we theoretically find to be compressible in hydrogen plasmas, suggesting this as a viable compression scheme for broadband soft-x-rays from HHG.

Stacking and twisting atom-thin sheets create superlattice structures with unique emergent properties, while tailored light fields can manipulate coherent electron transport on ultrafast timescales. The unification of these two approaches may lead to ultrafast creation and manipulation of band structure properties, which is a crucial objective for the advancement of quantum technology. Here, we address this by demonstrating a tailored lightwave-driven analogue to twisted layer stacking. This results in sub-femtosecond control of time-reversal symmetry breaking and thereby band structure engineering in a hexagonal boron nitride monolayer. The results practically demonstrate the realization of the topological Haldane model in an insulator. Twisting the lightwave relative to the lattice orientation enables switching between band configurations, providing unprecedented control over the magnitude and location of the band gap, and curvature. A resultant asymmetric population at complementary quantum valleys lead to a measurable valley Hall current, detected via optical harmonic polarimetry. The universality and robustness of the demonstrated sub-femtosecond control opens a new way to band structure engineering on the fly paving a way towards large-scale ultrafast quantum devices for real-world applications.

Abstract In recent years, the stacking and twisting of atom-thin structures with matching crystal symmetry has provided a unique handle to create new superlattice structures where new properties emerge1,2. In parallel, control over the temporal characteristics of strong light fields has allowed to manipulate coherent electron transport in such atom-thin structures on sub-laser-cycle timescales3,4. Here, we demonstrate a tailored lightwave-driven analogue to twisted layer stacking. Tailoring the spatial symmetry of the light waveform to that of the lattice of a hexagonal boron nitride monolayer, and twisting this waveform results in optical control of time-reversal symmetry breaking5, and the realization of the topological model of Haldane6,7 in the laser-dressed 2D insulating crystal. Further, the parameters of the effective Haldane-type Hamiltonian are controlled by the rotating light waveform, enabling ultrafast switching between band structure configurations and unprecedented control over the magnitude, location, and curvature of the band gap. A resultant asymmetric population at complementary quantum valleys leads to a measurable valley Hall current8, detected via optical harmonic polarimetry. The universality and robustness of our scheme opens the way to band engineering on the fly, unlocking the possibility to create few-femtosecond switches of quantum degrees of freedom.

We demonstrate high-contrast, intense single-cycle pulses by enhancing the self-phase modulation for spectral broadening in two-stage of all-solid-state multiple-plate setups. The output pulses are compressed to 2.6 fs, close to the transform-limited of 2.55 fs.

Regarded as the most important ion in interstellar chemistry, the trihydrogen cation, H_3^+ , plays a vital role in the formation of water and many complex organic molecules believed to be responsible for life in our universe. Apart from traditional plasma discharges, recent laboratory studies have focused on forming the trihydrogen cation from large organic molecules during their interactions with intense radiation and charged particles. In contrast, we present results on forming H_3^+ from bimolecular reactions that involve only an inorganic molecule, namely water, without the presence of any organic molecules to facilitate its formation. This generation of H_3^+ is enabled by “engineering” a suitable reaction environment comprising water-covered silica nanoparticles exposed to intense, femtosecond laser pulses. Similar, naturally-occurring, environments might exist in astrophysical settings where hydrated nanometer-sized dust particles are impacted by cosmic rays of charged particles or solar wind ions. Our results are a clear manifestation of how aerosolized nanoparticles in intense femtosecond laser fields can serve as a catalysts that enable exotic molecular entities to be produced via non-traditional routes.

Ultrafast light-induced molecular reactions on aerosolized nanoparticles may elucidate early steps in the photoactivity of nanoparticles with potential impact in fields ranging from chemistry and medicine to climate science. In situ morphology discrimination for nanoparticle streams when measuring light-induced reaction yields is crucial, but lacking. Here, we experimentally demonstrate, using the reaction nano-scopy technique, that proton momenta from deprotonation reactions induced by intense femtosecond pulses exhibit clear, distinguishable signatures for single silica nanospheres and their clusters. Our findings are supported by classical trajectory Monte Carlo simulations. The results demonstrate an in situ single-shot discrimination method between reaction yields from photoinduced processes on single particles and their clusters. We find that the ionization of clusters dominates at sufficiently low intensities, providing an explanation to resolve previously observed discrepancies between experimental data and theoretical treatments, which considered only single nanoparticles.

We use thin solid plates in a double stage multi-plate configuration to produce high-contrast, intense single-cycle pulse at 3 kHz. Generated spectrum spans from 400 to 1000 nm at -20 dB intensity level. Output pulses are compressed down to 2.6 fs (transform-limit 2.55 fs) with an energy of 0.235 mJ.

High-contrast, intense single-cycle pulses are highly desirable tools in ultrafast science, enabling highest temporal resolution, pushing matter to extreme conditions, and serving as drivers in petahertz electronics. In this Letter, we use thin solid plates in a double multi-plate supercontinuum configuration, delivering a broadband spectrum spanning from ∼ 400 to ∼ 1000 n m at the − 20 d B intensity level to produce a single-cycle pulse. We show that the spectral broadening by self-phase modulation with few-cycle pulses is more suitable for compression than the single-cycle limit than with multi-cycle pulses. The pulses are compressed to 2.6 fs pulses, close to the transform limit of 2.55 fs, with an energy of 0.235 mJ. They exhibit an excellent power stability of 0.5% rms over 3 h and a beam profile. The obtained single-cycle pulses can be utilized in many applications, such as generation of isolated attosecond pulses via high-order harmonic generation, investigation of ultrafast phenomena with extreme temporal resolution, or high-intensity laser-solid experiments.

A high-contrast 2.6 fs single-cycle pulse (transform-limited duration of 2.55 fs) has been demonstrated by optimizing self-phase modulation (SPM) and self-steepening (SS) effect in a double-stage of multiple thin plates

Nanoparticles offer unique properties as photocatalysts with large surface areas. Under irradiation with light, the associated near-fields can induce, enhance, and control molecular adsorbate reactions on the nanoscale. So far, however, there is no simple method available to spatially resolve the near-field induced reaction yield on the surface of nanoparticles. Here we close this gap by introducing reaction nanoscopy based on three-dimensional momentum-resolved photoionization. The technique is demonstrated for the spatially selective proton generation in few-cycle laser-induced dissociative ionization of ethanol and water on SiO 2 nanoparticles, resolving a pronounced variation across the particle surface. The results are modeled and reproduced qualitatively by electrostatic and quasi-classical mean-field Mie Monte-Carlo (M 3 C) calculations. Reaction nanoscopy is suited for a wide range of isolated nanosystems and can provide spatially resolved ultrafast reaction dynamics on nanoparticles, clusters, and droplets.

High harmonic generation (HHG) using intense laser pulses has long proven to be an extremely reliable source of high-energy, ultrashort (down to few tens of attoseconds) and coherent light radiation. This has promoted HHG as the tool of choice for numerous scientific applications. As understood by the three-step model, HHG is a highly nonlinear process which is strongly dependent on the classical electric field shapes of the driving laser pulse [1]. Thus, a common approach to control the HHG spectrum has been by modifying this electric field. Previous works in this direction primarily focused on weak perturbative approaches to either modify the ionization probability, suppress electron re-scattering by slight modification of the electron trajectory or use macroscopic manipulation of the generating medium. Our work focuses on a significantly less explored area [2,3], where the driving electric field structure is very strongly modified by a secondary field. This causes drastic changes in re-colliding electron trajectories, leading to highly modified HHG spectra as a function of their relative phase.

We report on a functional experimental design for Bessel beam generation capable of handling high-energy ultrashort pulses (up to 1.2 mJ per pulse of 50 fs duration). This allows us to deliver intensities exceeding the breakdown threshold for air or any dielectric along controlled micro-filaments with lengths exceeding 4 mm. It represents an unprecedented upscaling in comparison to recent femtosecond Bessel beam micromachining experiments. We produce void microchannels through glass substrates to demonstrate that aspect ratios exceeding 1200∶1 can be achieved by using single high-intensity pulses. This demonstration must lead to new methodologies for deep-drilling and high-speed cutting applications.