Monitoring coherent electron wave packet excitation dynamics by two-color attosecond laser pulses

Ultrafast attosecond-magnetic-field generation of the charge migration process based on HeH2+ and H2 + electronically excited by circularly polarized laser pulses

The ultrafast process by the electron in molecular ions from one site or region to another that has come to be known as charge migration (CM), which is of fundamental importance to photon induced chemical or physical reactions. In this work, we study the electron current and ultrafast magnetic-field generation based on CM process of oriented asymmetric (HeH²⁺) and symmetric (H₂ ⁺) molecular ions. Calculated results show that they are ascribed to quantum interference of electronic states for these molecular ions under intense circularly polarized (CP) laser pulses. The two scenarios of (i) resonance excitation and (ii) direct ionization are considered through appropriately utilizing designed laser pulses. By comparison, the magnetic field induced by the scenario (i) is stronger than that of scenario (ii) for molecular ions. However, the scheme (ii) is very sensitive to the helicity of CP field, which is opposite to the scenario (i). Moreover, the magnetic field generated by H₂ ⁺ is stronger than that by HeH²⁺ through scenario (i). Our findings provide a guiding principle for producing ultrafast magnetic fields in molecular systems for future research in ultrafast magneto-optics.

Ultrafast X-ray photoelectron diffraction in triatomic molecules by circularly polarized attosecond light pulses

We theoretically study ultrafast photoelectron diffraction in triatomic molecules with cyclic geometry by ultrafast circular soft X-ray attosecond pulses.

Probing Attosecond Electron Coherence in Molecular Charge Migration by Ultrafast X-Ray Photoelectron Imaging

Electron coherence is a fundamental quantum phenomenon in today’s ultrafast physics and chemistry research. Based on attosecond pump–probe schemes, ultrafast X-ray photoelectron imaging of molecules was used to monitor the coherent electron dynamics which is created by an XUV pulse. We performed simulations on the molecular ion H 2 + by numerically solving time-dependent Schrödinger equations. It was found that the X-ray photoelectron angular and momentum distributions depend on the time delay between the XUV pump and soft X-ray probe pulses. Varying the polarization and helicity of the soft X-ray probe pulse gave rise to a modulation of the time-resolved photoelectron distributions. The present results provide a new approach for exploring ultrafast coherent electron dynamics and charge migration in reactions of molecules on the attosecond time scale.

Monitoring the electron dynamics of the excited state via higher-order spectral minimum

A pump-probe scheme for monitoring the electron dynamics of the excited state has been investigated by numerically solving the two-state time-dependent Schrödinger equation based on the non-Born-Oppenheimer approximation. By adjusting the delay time between a mid-infrared probe pulse and an ultra violet pump pulse, an obvious minimum can be seen in the higher-order harmonic region. With electron probability density distribution, ionization rate and classical simulation, the minimum can be ascribed to the electron localization around one nucleus at larger delay time and represents the electron dynamics of the excited state at the time of ionization. Moreover, the position of the minimum is much more sensitive to the nuclear motion.

Attosecond Dynamics of Molecular Electronic Ring Currents

Ultrafast charge migration is of fundamental importance to photoinduced chemical reactions. However, exploring such a quantum dynamical process requires demanding spatial and temporal resolutions. We show how electronic coherence dynamics induced in molecules by a circularly polarized UV pulse can be tracked by using a time-delayed circularly polarized attosecond X-ray pulse. The X-ray probe spectra retrieve an image at different time delays, encoding instantaneous pump-induced circular charge migration information on an attosecond time scale. A time-dependent ultrafast electronic coherence associated with the periodical circular ring currents shows a strong dependence on the helicity of the UV pulse, which may provide a direct approach to access and control the electronic quantum coherence dynamics in photophysical and photochemical reactions in real time.

Exploring coherent electron excitation and migration dynamics by electron diffraction with ultrashort X-ray pulses

Exploring ultrafast charge migration is of great importance in biological and chemical reactions.