3D Characterization of Spatiotemporally Coupled High Harmonic Attosecond Pulses

Abstract Manipulation of ultrafast laser fields across the temporal, spatial, and spectral domains can result in a spatiotemporally coupled structure of light, which cannot be mathematically decomposed into the product of spatial and temporal profiles. However, this spatiotemporal coupling effect may degrade the focusability of ultrafast laser pulses at large‐scale laser facilities. As ultrafast science has advanced from femtosecond to attosecond time scales, coherent attosecond optical pulses have become accessible through high harmonic generation, an extremely nonlinear optical process that produces an enhanced spatiotemporal coupling effect. Limited studies have explored the spatiotemporal coupling of high harmonic attosecond pulses owing to the lack of 3D characterization of attosecond optical fields. This study addresses this limitation by providing a 3D characterizing of the spatiotemporal optical field profiles of high harmonic attosecond pulses and investigating their physical spatiotemporal coupling effects. The spatiotemporal coupling of high harmonic attosecond pulses is quantitatively evaluated via a newly defined parameter that incorporates phase contributions in the time‐space domain, which may likely correlate with the inhomogeneous intrinsic atomic dipole phase determined by the driving laser intensity. This physical insight, combined with the 3D optical field metrology, can potentially benefit extreme UV nonlinear optics and attosecond dynamic imaging.