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.

• Received 24 July 2017
• Revised 10 December 2017

DOI:https://doi.org/10.1103/PhysRevLett.120.093002