Attosecond spectroscopy holds great promise as a time-resolved general probe of electron correlation dynamics, which is central to important many-body phenomena from superconductivity to chemical bond formation. Double ionization processes are envisioned to be a direct probe of electron correlation by studying the time-resolved momentum correlation of two electrons. However, the time delay between two photoelectrons arising from double ionization has not been measured directly in the attosecond time domain, so it remains to be seen what such measurements can reveal concerning the details of electron correlation.
Recently, using a newly developed three-dimensional (3D) electron-electron coincidence imaging technique and an attosecond two-electron angular streaking method, we show the emission time delay between two electrons can be measured from zero attoseconds to more than one femtosecond. Surprisingly, in benzene, the double ionization rate decays as the time delay between the first and second electron emission increases during the first femtosecond.
With this new method, pump-probe studies of electron correlation dynamics at the attosecond time-scale have become a reality. In this talk, I will describe the development and some applications of this new method in studying ultrafast electronic and nuclear dynamics.