Kunlong Liu

Helicity sensitive enhancement of strong-field ionization in circularly polarized laser fields.

We investigate the strong-field ionization from p± orbitals driven by circularly polarized laser fields by solving the two-dimensional time-dependent Schrödinger equation in polar coordinates with the Lagrange mesh technique. Enhancement of ionization is found in the deep multiphoton ionization regime when the helicity of the laser field is opposite to that of the p electron, while this enhancement is suppressed when the helicities are the same. It is found that the enhancement of ionization is attributed to the multiphoton resonant excitation. The helicity sensitivity of the resonant enhancement is related to the different excitation-ionization channels in left and right circularly polarized laser fields.

Wavelength dependence of electron localization in the laser-driven dissociation of H2+

We theoretically investigate the laser wavelength dependence of asymmetric dissociation of H2(+). It is found that the electron localization in molecular dissociation is significantly manipulated by varying the wavelength of the driving field. Through creating a strong nuclear vibration in the laser-molecular interaction, our simulations demonstrate that the few-cycle mid-infrared pulse can effectively localize the electron at one of the dissociating nuclei with weak ionization. Moreover, we show that the observed phase-shift of the dissociation asymmetry is attributed to the different population transfers by the remaining fields after the internuclear distances reach the one-photon coupling point.

Phase dependence of electron localization in HeH 2+ dissociation with an intense few-cycle laser pulse

The electron localization in the dissociation of the asymmetric charged molecular ion HeH²⁺ exposed to an intense few-cycle laser pulse is studied by solving numerically the 3D time-dependent Schrödinger equation. By varying the carrier-envelope phase (CEP) and the intensity of the pulse, the upward shift of the localization probability and the suppression of the dissociation channel He²⁺+H are observed. Our analysis shows that the phenomenon is attributed to the asymmetric structure of the molecule as well as the recollision-assistant field-induced ionization of the electron wave packets localized on H⁺ in the trailing of the pulse.

Revealing correlated electronic and nuclear dynamics in molecules with energy-resolved population imaging

We explore a new fashion, named energy-resolved population image (EPI), to represent on an equal footing the temporary electronic transition and nuclear motion during laser-molecular interaction. By using the EPI we have intuitively demonstrated the population transfer in vibrational H

Tunneling site of electrons in strong-field-enhanced ionization of molecules

_2^+

Control of electron localization in highly excited states with two ultraviolet laser pulses

exposed to extreme ultraviolet pulses, revealing the energy sharing rule for the correlated electron and nuclei. We further show that the EPI can be extended to uncover the origins of the distinct energy sharing mechanisms in multi-photon and tunneling regimes. The present study has clarified a long-standing issue about the dissociative ionization of H

Anomalous isotopic effect on electron-directed reactivity by a 3-μm midinfrared pulse

_2^+

Dramatic cutoff extension and broadband supercontinuum generation in multi-cycle two color pulses.

and paves the way to identify instantaneous molecular dynamics in strong fields.

Ultrafast preparation and detection of ring currents in single atoms

We investigated electron emissions in strong field enhanced ionization of asymmetric diatomic molecules by quantum calculations. It is demonstrated that the widely-used intuitive physical picture, i.e., electron wave packet direct ionization from the up-field site (DIU), is incomplete. Besides DIU, we find another two new ionization channels, the field-induced excitation with subsequent ionization from the down-field site (ESID), and the up-field site (ESIU). The contributions from these channels depend on the molecular asymmetry and internuclear distance. Our work provides a more comprehensive physical picture for the long-standing issue about enhanced ionization of diatomic molecules.

Phase-locked ultra-broadband supercontinuum generation in a mid-infrared polarization gating

We propose and demonstrate a scheme for controlling the electron localization in the dissociating H2 in highly excited states. The control is achieved through two steps: the excitation and the coupling of the electronic wavepackets. Firstly, the excitation is triggered by an ultraviolet laser pulse with a critical wavelength, in which the wavepackets can be launched to the highly excited state ( σ 2s g )e fficiently from the ground state ( σ 1s g). Then, we utilize a second time-delayed ultraviolet laser pulse to manipulate the population of the degenerate state ( σ 3p u) around the one-photon coupling region. Our results show that, by adjusting the time delay between the two pulses and the carrier–envelope phase of the second pulse, the control of electron localization of H2 in highly excited states can be achieved.