Attosecond dynamic imaging: Basic ideas, results, and hopes

摘要

The goal of ‘attosecond dynamic imaging’ is to follow electronic and nuclear dynamics in atoms and molecules with attosecond temporal resolution, with the dream of accomplishing this goal for isolated molecules. Attosecond dynamic imaging also includes the idea of combining attosecond temporal and Angstrom-scale spatial resolution - that is, making movies of electronic and nuclear dynamics in individual molecules. One can try several approaches to realize this dream, and this tutorial will focus on one such route: I will describe the main theoretical and experimental ideas that form the basis of using intense infrared (IR) laser fields for attosecond dynamic imaging, with or without the assistance of attosecond XUV pulses. The key idea in this approach is to remove an electron from the very atom or molecule one wants to image, accelerate it in an intense infrared laser field, and then bring it back to interrogate the parent ion within a fraction of the IR laser cycle. The potential for temporal resolution in this technique comes from the brevity of the electron-parent ion collision, also known as re-collision. The potential for spatial resolution comes from the de-Broglie wavelength of the returning electron. The tutorial will touch upon the following topics: • Molecular alignment with short laser pulses; • Strong-field ionization of molecules and laser-driven electron-ion recollison; • Key processes of interest: ionization, high harmonic generation, laser-induced electron diffraction; • High harmonic emission: how is attosecond time-resolution encoded? • High harmonic tomography of molecular orbitals: what works, what doesn''t, and what can be learned (if anything); • High harmonic spectroscopy of attosecond hole migration; • Electron-ion entanglement and its consequences; • Photo-electron spectra: ‘direct’ and ‘recollision’ electrons. How is attosecond t--ime-resolution encoded? • Photo-electron spectroscopy of ionizing orbitals: what can we learn from ionization rates and spectra of ‘direct’ electrons? • Spectra of the ‘recollision electrons’: electron diffraction and electron holography. • Control of electron - ion recollision: applications of multi-color fields, ionization by XUV pulses, etc; • Main challenges and perspectives.