Spectral Phase Pulse Shaping Alters Photoionization Time
Photoionization is a key step in many attosecond processes. Accurately determining the photoionization time delay is critical to understanding electron dynamics during and after ionization and can guide future efforts to manipulate electron motion. Prior studies have shown that the photoionization time delay is non-zero and that pulse shaping through alteration of the spectral phase may change the number and timing of ionization events. In order to more quantitatively assess whether and how the spectral phase modifies the photoionization time delay, we use attosecond streaking simulations to extract the streaking time delay for ionizing pulses with identical power spectra, but different spectral phases. We compare streaking time delays for Gaussian, Airy, and fifth order phase extreme ultraviolet (XUV) pulses. We find that the streaking delay depends on the XUV spectral phase and that the sign of the delay is determined by the sign of the phase for large phases. Pulses with non-zero spectral phase show an asymmetry in the streaking spectrogram that is associated with phase-dependent spectral compression or broadening. Comparison of the streaking delays for short- and long-range potentials indicates that Coulomb-laser coupling contributions to the streaking shift are independent of spectral phase, confirming that the observed phase dependence arises from intrinsic photoionization dynamics. Overall, our work suggests that the spectral phase may open the door to new opportunities for controlling ionization timing and provide new avenues for coherent control of ultrafast electron