Real-Time Observation of Electron and Nuclear Dynamics in Nitric Oxide with High Harmonics in the Water Window

X-ray absorption spectroscopy (XAS) is a powerful technique to investigate local electronic structures of matter with element specificity. Recent development on high-harmonic generation (HHG) with long-wavelength, intense infrared (IR) light sources has enabled femto-to-attosecond XAS measurements in the soft X-ray (SX) region, especially in the water window (284–543 eV) [1–3]. Here, we report on a time-resolved XAS measurement of nitric oxide (NO) at the N K-edge (400 eV). We observe AC Stark shift and tunnel ionization induced by a strong IR field as well as the subsequent nuclear dynamics.