Preparing attosecond coherences by strong-field ionization

Abstract

Strong-field ionization (SFI) has been shown to prepare wave packets with few-femtosecond periods. Here, we explore whether this technique can be extended to the attosecond time scale. We introduce an intuitive model, which is based on the Fourier transform of the subcycle SFI rate, for predicting the bandwidth of ionic states that can be coherently prepared by SFI. The coherent bandwidth decreases considerably with increasing central wavelength of the ionizing pulse but it is much less sensitive to its intensity. Many-body calculations based on time-dependent configuration-interaction singles support these results. The influence of channel interactions and laser-induced dynamics within the ion is discussed. Our results further predict that multicycle femtosecond pulses can coherently prepare subfemtosecond wave packets with higher selectivity and versatility compared to single-cycle pulses with an additional sensitivity to the mutual parity of the prepared states.

Charge migration and charge transfer in molecular systems

“…The case of strong-field ionization has been studied in the most general context in Ref. 61 and single-photon ionization in Ref. 62.…”

“…These considerations apply to both single-photon and strong-field ionizations, but some subtleties remain. The requirement of overlap in the kinetic-energy domain is sufficient in the case of single-photon ionization with Fourier-transform-limited pulses, but not in the case of strong-field ionization 61 . In the latter case, the photoelectron spectra are usually extremely broad, such that another factor becomes dominant, which is the temporal confinement of ionization.…”

“…In the latter case, the photoelectron spectra are usually extremely broad, such that another factor becomes dominant, which is the temporal confinement of ionization. Reference 61 shows that the Fourier-transform of the instantaneous ionization rate provides a good measure of the spectral bandwidth over which strong-field ionization can prepare coherence. This “coherence window” has a typical width of ∼4 eV for ionization by an 800-nm pulse, such that charge migration with periods only longer than ∼1 fs can be initiated with a high degree of coherence by strong-field ionization with 800-nm pulses.…”

“…More recent theoretical results introduced the concept of a general coherence window which suggests that strong-field ionization by 800-nm fields is generally capable of triggering charge migration with periods down to ∼1 fs, increasing with longer wavelengths 61 . The most important remaining questions concern the lifetime of the electronic coherence that drives charge migration, the interplay of charge migration and nuclear motion to reach a long-lived state with a localized charge, i.e., charge transfer, and finally the effect of this charge transfer on the subsequent chemical-reaction pathways of the molecule.…”

Correlation-driven charge migration following double ionization and attosecond transient absorption spectroscopy

“…These pure electron dynamics discussed can occur in many situations in which multiple electrons are promptly removed from a molecule, i.e., when the electron removal occurs during a time span that is short compared to the dynamical timescales associated with valence excitations. Such situations can be the consequence of attosecond ionization which can be induced by either attosecond light pulses or by strong-field ionization [7][8][9]. Importantly, prompt removal of multiple electrons can also be the result of electronic decay processes that follow for instance inner-shell ionization.…”