Ultrafast Time-Correlation Transduction: Probing High-Harmonic Generation Dynamics*

Recent advancements in ultrafast optical technology have enabled the investigation of nuclear and electron dynamics on an attosecond time scale using extreme ultraviolet (XUV) and soft X-ray radiation generated through high-harmonic generation (HHG). The ability to probe the critical electric field strength, which pertains to quantum electrodynamics (QED) in a nonperturbative regime, allows for profound insights into strong-field quantum electrodynamics (SF-QED). In strong-field conditions, HHG is characterized by a three-step model: electron tunneling from its atomic potential, acceleration in the continuum, and photon emission upon recombination. Classical models inadequately account for electron-core interactions, leading to discrepancies with experimental measurements. ​Here, we introduce ultrafast time-correlation transduction (TCT), a novel technique aimed at characterizing the distinctions between perturbative and nonperturbative processes in HHG.​

TCT utilizes a high-energy laser pulse, which is divided into orthogonal wave packets for the investigation of HHG dynamics. The method precisely captures the timing of emissions during the HHG three-step process, enabling attosecond-level measurements of quantum dynamics with applications beyond HHG, including explorations of axion-like particles (ALPs) in astrophysical contexts. We present simulations demonstrating the efficacy of TCT across various quantum materials, revealing notable sensitivities at specific operational wavelengths. The findings emphasize the interplay between semi-classical and full quantum systems in HHG and propose TCT as a powerful tool for elucidating the complexities of quantum photo-electrodynamics, thereby advancing our understanding of attosecond science and its implications for quantum optics and information science.