Understanding the role of phase in chemical bond breaking with coincidence angular streaking

Abstract

Electron motion in chemical bonds occurs on an attosecond timescale. This ultrafast motion can be driven by strong laser fields. Ultrashort asymmetric laser pulses are known to direct electrons to a certain direction. But do symmetric laser pulses destroy symmetry in breaking chemical bonds? Here we answer this question in the affirmative by employing a two-particle coincidence technique to investigate the ionization and fragmentation of H 2 by a long circularly polarized multicycle femtosecond laser pulse. Angular streaking and the coincidence detection of electrons and ions are employed to recover the phase of the electric field, at the instant of ionization and in the molecular frame, revealing a phase-dependent anisotropy in the angular distribution of H þ fragments. Our results show that electron localization and asymmetrical breaking of molecular bonds are ubiquitous, even in symmetric laser pulses. The technique we describe is robust and provides a powerful tool for ultrafast science.

Photoelectron momentum distributions of atomic and molecular systems in strong circularly or elliptically polarized laser fields

“…When H 2 + is exposed to strong laser fields, the electron hops between two nuclei. It was demonstrated that the electron leaves the molecule from the uphill potential well [68]. Depending on the laser wavelength (and other laser parameters), the electron localizes to the uphill well at different timings, and hence the timing of the electron release is also expected to fluctuate.…”

“…In fact, in studies of H 2 + , it has been pointed out that the electron wave packet does not leave the parent ion when the electric field is parallel to the molecular axis, as expected by the QSTI picture, but at a delayed timing [44,46], and that the wave packet has a non-negligible initial flow velocity [44,46,48]. These effects, originating from the bound electron dynamics prior to ionization [65][66][67][68], are considered to be specific to the molecular systems. For multielectron systems, it has been pointed out that the interaction of the photoelectron with the laser-induced dipole of the parent ion also influences the PMD [30,38,41,50].…”

“…Hence, the deviations, which break the fourfold symmetry of the PMD expected by the SFA, are sometimes called Coulomb asymmetry. On the other hand, the multicenter character and the nuclear motion of molecules generally have been known to induce unique phenomena absent in atomic systems [54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71]. In fact, in studies of H 2 + , it has been pointed out that the electron wave packet does not leave the parent ion when the electric field is parallel to the molecular axis, as expected by the QSTI picture, but at a delayed timing [44,46], and that the wave packet has a non-negligible initial flow velocity [44,46,48].…”

Multielectron effects in strong-field dissociative ionization of molecules

“…1(b), we applied the angular streaking technique [11,[22][23][24][25][26][27] and COLTRIMS [20] using single-color, elliptically polarized pulses. Laser pulses (35 fs, 790 nm, polarization ellipticity ε ß 0.68) from an 8-kHz Ti:sapphire multipass amplifier were focused by a concave mirror (ƒ = 7.5 cm) into a supersonic N 2 gas jet in the vacuum chamber.…”

Carrier-Envelope-Phase Characterization for an Isolated Attosecond Pulse by Angular Streaking

“…Note that angular streaking cameras have been used to unveil several interesting phenomena [28][29][30][31]. In our strategy, the prototypical hydrogen atom is tunneling ionized by the overlapped IAP-IR field.…”