Recent advances in high-order harmonic generation have made it possible to use a tabletop-scale setup to produce spatially and temporally coherent beams of light with bandwidth spanning 12 octaves, from the ultraviolet up to x-ray photon energies $>1.6\mathrm{keV}$. Here we demonstrate the use of this light for x-ray-absorption spectroscopy at the $K$- and $L$-absorption edges of solids at photon energies near 1 keV. We also report x-ray-absorption spectroscopy in the water window spectral region (284–543 eV) using a high flux high-order harmonic generation x-ray supercontinuum with ${10}^9\text{photons}/\mathrm{s}$ in 1% bandwidth, 3 orders of magnitude larger than has previously been possible using tabletop sources. Since this x-ray radiation emerges as a single attosecond-to-femtosecond pulse with peak brightness exceeding ${10}^{26}\text{photons}/\mathrm{s}/{\mathrm{mrad}}^2/{\mathrm{mm}}^2/1\%$ bandwidth, these novel coherent x-ray sources are ideal for probing the fastest molecular and materials processes on femtosecond-to-attosecond time scales and picometer length scales.

Imaging and controlling reactions in molecules and materials at the level of electrons is a grand challenge in science, relevant to our understanding of charge transfer processes in chemistry, physics, and biology, as well as material dynamics. Direct access to the dynamic electron density as electrons are shared or transferred between atoms in a chemical bond would greatly improve our understanding of molecular bonding and structure. Using reaction microscope techniques, we show that we can capture how the entire valence shell electron density in a molecule rearranges, from molecular-like to atomic-like, as a bond breaks. An intense ultrashort laser pulse is used to ionize a bromine molecule at different times during dissociation, and we measure the total ionization signal and the angular distribution of the ionization yield. Using this technique, we can observe density changes over a surprisingly long time and distance, allowing us to see that the electrons do not localize onto the individual Br atoms until the fragments are far apart (∼5.5 Å ), in a region where the potential energy curves for the dissociation are nearly degenerate. Our observations agree well with calculations of the strong-field ionization rates of the bromine molecule.

Significance: Electron–electron interactions are among the fastest processes in materials that determine their fascinating properties, occurring on attosecond timescales on up (1 as = 10 ⁻¹⁸ s). The recent development of attosecond angle-resolved photoemission spectroscopy (atto-ARPES) using high harmonic generation has opened up the possibility of probing electron–electron interactions in real time. In this paper, we distinguish electron–electron screening and charge scattering in the time domain in individual energy bands within a solid. These results open up new possibilities for probing fundamental electron–electron interactions in a host of materials including magnetic, superconducting, and advanced quantum materials.

Significance: The interactions between electrons and lattice vibrations called phonons not only determine the properties of materials, but also give rise to remarkable phenomena such as superconductivity or spatial ordering of the charges and lattice. Here, we use a femtosecond laser to excite and spatially relocate electrons in TaSe ₂ . In all observations to date, these excited electrons cool monotonically by scattering with phonons. Surprisingly, we observe an oscillation of the electron temperature that is coupled with the lattice breathing mode, and a switching in the dominant electron–phonon interactions by varying the laser excitation. Our results demonstrate a promising way to manipulate electron–phonon interactions, opening up routes to steer a quantum material toward a desired state using light.

Imaging using coherent extreme-ultraviolet (EUV) light provides exceptional capabilities for the characterization of the composition and geometry of nanostructures by probing with high spatial resolution and elemental specificity. We present a multi-modal tabletop EUV imaging reflectometer for high-fidelity metrology of nanostructures. The reflectometer is capable of measurements in three distinct modes: intensity reflectometry, scatterometry, and imaging reflectometry, where each mode addresses different nanostructure characterization challenges. We demonstrate the system’s unique ability to quantitatively and non-destructively measure the geometry and composition of nanostructures with tens of square microns field of view and sub-nanometer precision. Parameters such as surface and line edge roughness, density, nanostructure linewidth, and profile, as well as depth-resolved composition, can be quantitatively determined. The results highlight the applicability of EUV metrology to address a wide range of semiconductor and materials science challenges.

Nanostructuring on length scales corresponding to phonon mean free paths provides control over heat flow in semiconductors and makes it possible to engineer their thermal properties. However, the influence of boundaries limits the validity of bulk models, while first-principles calculations are too computationally expensive to model real devices. Here we use extreme ultraviolet beams to study phonon transport dynamics in a 3D nanostructured silicon metalattice with deep nanoscale feature size and observe dramatically reduced thermal conductivity relative to bulk. To explain this behavior, we develop a predictive theory wherein thermal conduction separates into a geometric permeability component and an intrinsic viscous contribution, arising from a new and universal effect of nanoscale confinement on phonon flow. Using experiments and atomistic simulations, we show that our theory applies to a general set of highly confined silicon nanosystems, from metalattices, nanomeshes, porous nanowires, to nanowire networks, of great interest for next-generation energy-efficient devices.