Femtosecond Soft-X-ray Absorption Spectroscopy of Liquids with a Water-Window High-Harmonic Source

Abstract

Femtosecond X-ray absorption spectroscopy (XAS) is a powerful method to investigate the dynamical behavior of a system after photoabsorption in real time. So far, the application of this technique has remained limited to large-scale facilities, such as femtosliced synchrotrons and free-electron lasers (FEL). In this work, we demonstrate femtosecond time-resolved soft-X-ray absorption spectroscopy of liquid samples by combining a sub-micrometer-thin flat liquid jet with a high-harmonic tabletop source covering the entire water-window range (284–538 eV). Our work represents the first extension of tabletop XAS to the oxygen edge of a chemical sample in the liquid phase. In the time domain, our measurements resolve the gradual appearance of absorption features below the carbon K-edge of ethanol and methanol during strong-field ionization and trace the valence-shell ionization dynamics of the liquid alcohols with a temporal resolution of ∼30 fs. This technique opens unique opportunities to study molecular dynamics of chemical systems in the liquid phase with elemental, orbital, and site sensitivity.

Temperature Measurements of Liquid Flat Jets in Vacuum

“…In both setups, we use a high-pressure liquid-chromatography (HPLC) pump to deliver the samples to the nozzles. 18 The vacuum in the experimental chamber typically ranges between 5 × 10 −3 to 1 × 10 −2 millibar during the measurements. In order to keep acceptable vacuum conditions, the sample is captured in a cold trap at liquid-nitrogen temperature.…”

“…For the collision-based flatjet 8,16,18 , two cylindrical liquid jets from two quartz nozzles of equal inner diameters (either 18 µm or 60 µm) collide at an angle of 48 • and generate a flatjet with a thickness that can be as thin as 500 nm, as assessed by white-light interferometry.…”

“…[11][12][13][14] Recent reported thicknesses reach 100 nm for both colliding jets and gas-dynamic jet. [8][9][10]15 These submicron-thickness flatjets have enabled several novel achievements in science, such as investigating liquid samples using high-order harmonic spectroscopy 16,17 , fs-transient XAS 18 , angular photoelectron spectroscopy 19 , and fs-electron scattering in liquids 20 . Despite these advantages and applications, an essential property of flatjets in vacuum, i.e.…”

Broadband X-Ray Absorption Spectra from Time-Dependent Kohn-Sham Calculations

“…Quantum chemistry is currently witnessing a resurgence of interest in x-ray spectroscopy, [1][2][3][4][5][6][7] catalyzed by the emergence of new technologies including coherent ultrahigh harmonic generation, 8 providing capabilities for ultrafast time resolution at x-ray wavelengths, [9][10][11] even with tabletop laser systems. 12 This technology has enabled x-ray absorption spectroscopy (XAS) and x-ray photoelectron spectroscopy (XPS) studies of solution-phase systems, [13][14][15][16] as well as surface-sensitive ultrafast spectroscopy at extreme ultraviolet (XUV) wavelengths. 17 Insofar as XAS is a widely-used tool to study to interrogate bonding and oxidation state, these advances offer the possibility to study element-specific charge dynamics with ultrafast time resolution, and electronic structure theory will undoubtedly play a major role in interpreting the results.…”

Apparatus for generation of nanojoule-class water-window high-order harmonics

“…Optical parametric amplification (OPA) lasers are capable of generating longer wavelengths compared to Ti:sapphire counterparts. Many groups capitalized on this advantage and generated HHs in the water window region [12][13][14][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] and used them for various applications [45][46][47] . At the same time, OPA lasers have several drawbacks.…”