Electron-positron pair production in ultrastrong laser fields

Electronepositron pair production due to the decay of vacuum in ultrastrong laser fields is an interesting topic which is revived recently because of the rapid development of current laser technology.The theoretical and numerical research progress of this challenging topic is reviewed.Many new findings are presented by different approaches such as the worldline instantons,the S-matrix theory,the kinetic method by solving the quantum Vlasov equation or/and the real-time DiraceHeisenbergeWigner formalism,the computational quantum field theory by solving the Dirac equation and so on.In particular,the effects of electric field polarizations on pair production are unveiled with different patterns of created momentum spectra.The effects of polarizations on the number density of created particles and the nonperturbative signatures of multiphoton process are also presented.The competitive interplay between the multiphoton process and nonperturbation process plays a key role in these new findings.These newly discovered phenomena are valuable to deepen the understanding of pair production in complex fields and even have an implication to the study of strong-field ionization.More recent studies on the pair production in complex fields as well as beyond laser fields are briefly presented in the view point of perspective future.

HeTDSE:A GPU based program to solve the full-dimensional time-dependent Schr?dinger equation for two-electron helium subjected to strong laser fields

Electron–electron correlation plays an important role in the underlying dynamics in physics and chemistry.Helium is the simplest and most fundamental two-electron system.The dynamic process of helium in a strong laser field is still a challenging issue because of the large calculation cost.In this study,a graphic processing unit(GPU)open ACC based ab initio numerical simulations package He TDSE is developed to solve the full-dimensional time-dependent Schrodinger equation of helium subjected to a strong laser pulse.He TDSE uses B-spline basis sets expansion method to construct the radial part of the wavefunction,and the spherical harmonic functions is used to express for the angular part.Adams algorithm is employed for the time propagation.Our example shows that He TDSE running on an NVIDIA Kepler K20 GPU can outperform the one on an Intel E5-2640 single CPU core by a factor of 147.He TDSE code package can be obtained from the author or from the author's personal website(doi:10.13140/RG.2.2.15334.45128)directly under the GPL license,so He TDSE can be downloaded,used and modified freely.

Nonadiabatic molecular dynamics simulation of C2H^2+2 in a strong laser field

We investigate the alignment dependence of the strong laser dissociation dynamics of molecule C2H2^2+ in the frame of real-time and real-space time-dependent density function theory coupled with nonadiabatic quantum molecular dynamics(TDDFT-MD) simulation.This work is based on a recent experiment study "ultrafast electron diffraction imaging of bond breaking in di-ionized acetylene" [Wolter et al.Science 354,308-3 12(2016)].Our simulations are in excellent agreement with the experimental data and the analysis confirms that the alignment dependence of the proton dissociation dynamics comes from the electron response of the driving laser pulse.Our results validate the ability of the TDDFT-MD method to reveal the underlying mechanism of experimentally observed and control molecular dissociation dynamics.

Theoretical study of the odd-even-order harmonic generation for asymmetric ions in non-Born-Oppenheimer approximation

We calculated the harmonic spectra generated from the asymmetric molecules of HD^＋ and HeH^2＋. It is found that HD＋produces only odd harmonics, while HeH^2＋produces both odd and even harmonics. Further analysis reveals that for both HD^＋ and HeH^2＋, the nuclear dipole acceleration can generate even harmonics, but it is three orders of magnitude lower than that of the electron. Hence, the electronic dipole acceleration dominates the harmonic generation. For HD^＋,the electronic dipole acceleration only contributes to the generation of odd harmonics, but for HeH^2＋it contributes to the generation of both odd and even harmonics. Besides, one concept of the broken degree of system-symmetry is proposed to explain the different odd-even property between the harmonic spectra of HD^＋ and HeH^2＋.

Control of molecular excitation during the plasma generation of a femtosecond laser pulse

From a classical dynamic simulation,we find the kinetic energy of the electrons generated during laser plasma generation depends on the laser polarization and intensity.The electron kinetic energy reaches its maximum with a fixed laser intensity for circularly polarized laser pulse.The fluorescence spectra at 380.4 nm from N2 and 391.3 nm from N2^＋ are measured;these are generated by both the direct excitation and electron collision excitation.The electron collision excitation is determined by the electron energy and reaches the maximal with a circularly polarized pulse.