Attosecond soft-X-ray spectroscopy in the gas and liquid phases*

Attosecond spectroscopy has the potential to address fundamental questions in chemical sciences. A promising approach is offered by the element- and site-sensitivity of X-ray spectroscopy. We have recently demonstrated the potential of table-top X-ray absorption spectroscopy with a water-window high-harmonic source, observing the temporal evolution of unoccupied molecular orbitals and molecular shape resonances during chemical reactions [1]. Compressing the mid-infrared driving pulses to less than 2 optical cycles, we have demonstrated the extension of this light source to fully cover the oxygen K-edge [2]. Using the same technique, we have also demonstrated the generation of isolated attosecond pulses, which have established a new record of the shortest light pulses ever measured (43 attoseconds) [3].
Since the vast majority of chemical processes takes place in the liquid phase, the extension of attosecond spectroscopy to liquids is desirable. I will discuss the first observation of extreme-ultraviolet high-harmomic generation from liquids, achieved through the application of ultrathin (0.6-2 μm) flat microjets [4]. I will also present the extension of attosecond time-resolved spectroscopy from molecules [5] to liquids [6]. The time delays between photoemission from gaseous and liquid water range from 50-70 attoseconds and are shown to mainly originate from the solvation of water molecules, with liquid-phase electron scattering playing a minor role. These developments set the stage for attosecond time-resolved studies of molecular systems of chemical complexity.

1. Y. Pertot et al., Science 355, 264 (2017)
2. C. Schmidt et al., Opt. Exp. 26, 11834 (2018)
3. T. Gaumnitz et al., Opt. Exp. 25, 27506 (2017)
4. T. T. Luu et al., Nature Communications 9, 3723 (2018)
5. M. Huppert et al., Phys. Rev. Lett. 117, 093001 (2016)
6. I. Jordan et al.,submitted (2019)