Electron vortices in photoionization by a pair of elliptically polarized attosecond pulses

The photoionization by two elliptically polarized, time delayed attosecond pulses is investigated to display a momentum distribution having the helical vortex or ring structuresi The results are obtained by the strong field approximation method and analyzed by the pulse decomposition. The ellipticities and time delay of the two attosecond pulses are found to determine the rotational symmetry and the number of vortex arms. For observing these vortex patterns, the energy bandwidth and temnoral duration of the attosecond pulses are ideal.

Laser Polarization Effect on Molecular Harmonic and Elliptically Polarized Attosecond Pulse Generation

Molecular harmonic spectra of H+2driven by the linearly polarized laser pulses with different polarized angles have been theoretically investigated through solving the two-dimensional time-dependent Schr¨odinger equation.(i) Below-threshold harmonic spectra show a visible enhanced peak around the 7th harmonic(H7), which produces a red-shift phenomenon as the internuclear distance increased. Theoretical analyses show the red-shift enhanced peak is caused by the laser-induced electron transfer between the ground state and the 1st excited state of H+2.(ii) Due to the two-centre interference phenomenon, the above-threshold harmonic spectra exhibit many maxima and minima.(iii)With the introduction of the polarized angle, the anomalous elliptically polarized harmonics can be found. But, with the introduction of the spatial inhomogeneous effect, not only the ellipticities of the harmonics are equal to a stable value of ε～ 0.1–0.3, but also the harmonic cutoffs are extended. As a result, four super-bandwidths of 407 e V, 310 e V,389 e V, and 581 e V can be obtained. Time profiles of the harmonic generations have been shown to explain the harmonic characteristics. Finally, a series of elliptically polarized(ε～ 0.1–0.3) attosecond X-ray pulses with durations from 18 as to 25 as can be directly produced through Fourier transformation of the spectral continuum.

Photoelectron momentum distributions of single-photon ionization under a pair of elliptically polarized attosecond laser pulses

The attosecond ionization dynamics of atoms has attracted extensive attention in these days.However,the role of the initial state is not clearly understood.To address this question,we perform simulations on the neon atom and its model atom with different initial states by numerically solving the corresponding two-dimensional time-dependent Schrodinger¨equations.We theoretically investigate atomic photoelectron momentum distributions(PMDs)by a pair of elliptically polarized attosecond laser pulses.We find that the PMD is sensitive not only to the ellipticities of the pulses,the relative helicity,and time delay of the pulses,but also to the symmetry of the initial electronic states.Results are analyzed by the first-order time-dependent perturbation theory(TDPT)and offer a new tool for detecting the rotation direction of the ring currents.