Probing Time-Dependent Molecular Dipoles on the Attosecond Time Scale

Abstract

Photoinduced molecular processes start with the interaction of the instantaneous electric field of the incident light with the electronic degrees of freedom. This early attosecond electronic motion impacts the fate of the photoinduced reactions. We report the first observation of attosecond time scale electron dynamics in a series of small- and medium-sized neutral molecules (N(2), CO(2), and C(2)H(4)), monitoring time-dependent variations of the parent molecular ion yield in the ionization by an attosecond pulse, and thereby probing the time-dependent dipole induced by a moderately strong near-infrared laser field. This approach can be generalized to other molecular species and may be regarded as a first example of molecular attosecond Stark spectroscopy.

On the analysis of photo-electron spectra

“…There remain widely disputed questions on the mechanisms underlying the response of the system to such complex excitations. A typical observable here is the total ionisation which is found to oscillate with the delay between IR pulse and attotrain [26,27,59]. Our preliminary computations show that these modulations are (not surprisingly) directly reflected in the PES.…”

“…In most experiments [26,27,43,44,45], an IR fs pulse is used to generate high harmonics which then serve to produce the coherent attotrain, which is usually modulated by an envelop that we denoted by g in Eq. (5c).…”

“…(5a) represents a considerably complicated pulse and that it will provide a critical test case for our analysis. Finally, we will consider the superposition of an IR fs pulse and a UV attotrain, as encountered in experiments [26,27,43,44,45]. This case will represent the most difficult excitation mechanism to be understood.…”

“…The latter ones even provide a time-resolved access to dynamics, at ionic pace with femtosecond (fs) [21,22] down to electronic pace with attosecond (as) pulses [23,24,25,26,27]. The PES of course remains a highly valuable tool of investigation of the dynamics, as it basically provides insight into electronic dynamics via ionization characteristics.…”

Spatial and temporal control of populations, branching ratios, and electronic coherences in LiH by a single one-cycle infrared pulse

“…Electron localization has been probed in diatomic cations [8][9][10][11][12] and larger systems [13][14][15][16] using pump-probe schemes involving atto and fs optical pulses. In these experiments the molecule is locally ionized by the pump which creates a non stationary state in the cation.…”