Abstract
We theoretically study pulse phase and helicity effects on ultrafast magnetic field generation in intense bichromatic circularly polarized laser fields. Simulations are performed on the aligned molecular ion H2+ from numerical solutions of corresponding time-dependent Schrödinger equations. We demonstrate how electron coherent resonant excitation influences the phase and helicity of the optically induced magnetic field generation. The dependence of the generated magnetic field on the pulse phase arises from the interference effect between multiple excitation and ionization pathways, and is shown to be sensitive to molecular alignment and laser polarization. Molecular resonant excitation induces coherent ring electron currents, giving enhancement or suppression of the phase dependence. Pulse helicity effects control laser-induced electron dynamics in bichromatic circular polarization excitation. These phenomena are demonstrated by a molecular attosecond photoionization model and coherent electron current theory. The results offer a guiding principle for generating ultrafast magnetic fields and for studying coherent electron dynamics in complex molecular systems.
Highlights
Imaging and manipulating molecular electron dynamics is one of the main goals in photophysical processes and photochemical reactions
Pairs of circularly polarized harmonics of different frequency and helicity can be prepared by a combination of pairs of counter-rotating circularly polarized laser pulses at different frequencies [62]
The molecular ion H+2 is aligned along the x/z axis, the two X-ray ultra violet (XUV) pulses with their field polarization vectors in the (x,y) plane propagate along the z axis, as illustrated in Figure 1A, for
Summary
Imaging and manipulating molecular electron dynamics is one of the main goals in photophysical processes and photochemical reactions. By creating unidirectional constant valence-type electronic currents in molecules with circularly polarized UV laser pulses, static magnetic fields [7,8,9] can be efficiently generated by the excitation of resonant degenerate orbitals. These laser-induced magnetic fields are much larger than those obtained by traditional static field methods [14]. Time-dependent circular coherent electron wave packets (CEWPs) and currents are created as superposition of bound-continuum states They become the source of intense time-dependent internal magnetic fields generated on attosecond timescale. The induced attosecond magnetic fields have been shown to be a function of various laser pulse parameters, such as the pulse intensity, wavelength, and duration [25, 26], providing new tools for control of ultrafast optical magnetism generation [27,28,29,30,31]
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