Direct imaging of molecular dynamics is a long-standing goal in physics and chemistry. As an emerging tool, high-order-harmonic spectroscopy (HHS) enables accessing molecular dynamics on femtosecond to attosecond time scales. However, decoding information from the harmonic signals is usually painstaking due to the coherent nature of high-order-harmonic generation (HHG). Here we show that this obstacle can be effectively overcome by exploiting machine learning in HHS. Combining the machine learning with an angle-resolved HHS method, the molecular movie with femtosecond resolution is reconstructed from the angular distributions of HHG measured at various time delays of the probe pulse. Such a movie distinctly shows the full information of the coherent rotational dynamics of molecules, which is unattained in previous studies. The experimental retrievals are in good agreement with the numerical simulations. Our findings provide a comprehensive picture of molecular rotation in space and time, which will facilitate the development of related research on molecular dynamics imaging.

• Received 14 February 2019

DOI:https://doi.org/10.1103/PhysRevA.99.053419