A 2D Holographic Approach for All-Optical Single-Shot Temporal Characterization of SASE FEL Pulses
X-ray Free-electron lasers (XFELs) deliver ultrashort and ultrabright radiation in a photon-energy range spanning from extreme ultraviolet to hard X-rays. Supporting pulse durations down to hundreds of attoseconds, these sources are unique in enabling imaging of matter with unprecedented temporal and spatial resolution. However, schemes that produce such ultrashort pulses typically rely on Self-Amplified Spontaneous Emission (SASE), a stochastic process that introduces significant temporal and spectral jitter, therefore requiring single-shot characterization methods for post sorting the acquired data. Although various methods have been developed for pulse characterization and delay tagging, they often come with experimental and computational complexity. Moreover, no existing method currently combines both single-shot pulse reconstruction and delay tagging at the attosecond time scale. To close this gap, we present two-dimensional time-domain Double-Blind Holography (2D-TDDBH), an entirely novel approach combining double-blind holography with concepts from diffractive imaging and ptychography. By recording the 2D spatial profile of the spectral interference between an extreme ultraviolet (XUV) FEL source and a high-harmonic generation (HHG)-based source, we achieve simultaneous waveform reconstruction and delay tagging of sub-10 fs FEL pulses with attosecond precision.