|
We describe how time and energy correlations between the electrons can be used to trace the dynamics of correlated two-electron ionization with sub-femtosecond precision, without using sub-femtosecond pulses. The approach is illustrated using the example of Auger or Coster-Kronig decay triggered by photo-ionization with an XUV pulse. It requires correlated measurements of angle-resolved energy spectra of both the photo- and Auger electrons in the presence of a laser pulse. Neither the XUV, nor the laser pulse have to be short compared to the decay time. We begin complete characterization of a process by reconstructing amplitude and phase of a correlated two-electron spectrum. Phase information is obtained in a manner similar to SPIDER reconstruction method of conventional ultrafast spectroscopy, where there is no fundamental limit to time resolution. Spectral phase is mapped onto amplitude modulation of spectral intensity by recording the interference of the original spectrum with its spectrally-shifted replica. Particle correlation also allows us to effectively solve the deconvolution problem, uncovering the fast component of the correlated process. One essential requirement, however, is temporal stability of the probe pulse relative to the pump: their relative jitter degrades time resolution. Fortunately, modern few-cycle infrared (IR) femtosecond pulses can be phase-stabilized with incredible attosecond precision over very long times, naturally leading to attosecond stabilization of XUV pulses which they generate [R. Kienberger et al. Nature 427, 817, (2004)]. Our approach can be used for any process resulting in the emission of two charged particles with fixed total energy. Examples are shake-off in one-photon two-electron ionization, photo-induced Auger or Coster-Kronig decay, etc. Ultrafast stages of such processes which can be time-resolved with our approach can also include Zeno and anti-Zeno stages of decay, core rearrangement, non-exponential decay due to structured continuum, etc. |
|