Theoretical Study Of Photoelectron Momentum Spectra Of Atoms And Molecules By Intense Laser Pulses

The interaction between laser and matter is a basic physical process.Studying the physical phenomena in the process can help people understand the material world in depth.The development of ultra-short and ultra-strong laser pulses meets the technical needs of related fields.People can detect and control photophysical and photochemical processes on ultra-short time scales and ultra-micro spatial scales,which provides the possibility for discovering new laws of physics for studying the interaction between lasers and matter,and realizes the dream of human beings to understand ultra-fast phenomena in the microscopic world.The coherent regulation of electronic states by laser pulses is the core issue in the study of ultrafast processes,and it is also one of the international frontiers.The information of the ultrafast dynamics of atoms and molecules is contained in the photoelectron momentum.Researchers could use the photoelectron momentum distribution(PMD)and photoelectron angular distribution(PAD)to detect the motion of electrons and the structure of matter.This paper systematically studies the PMD and PAD of He⁺ions,H₂⁺molecules and N₂ molecules,which is explicitly described:We theoretically study the PMD and PAD of the He⁺ions,H₂⁺and N₂ molecules in orthogonally polarized laser fields.The PMD and PAD are obtained by solving the two-dimensional(2D)time-dependent Schr(?)dinger equation(TDSE).The PMD and PAD are dependent on the time delay between the orthogonally polarized laser pulses,which comes from the interference between coherent electron wave-packets.The interference in the PMD and PAD of He⁺ions is created by the time delay of two orthogonally polarized laser pulses.There are two reasons for the interference in the PMD and PAD of H₂⁺and N₂ molecules:on the one hand,the interference is created by the time delay of two orthogonally polarized laser pulses,on the other hand,the interference is created by two-center ionization.The ultrafast photoionization model and the evolution of the electron wave-packets are adopted to describe these results given above.We theoretically study the PMD and PAD of N₂ molecules by solving 2D TDSE within frozen-nuclei and single-electron approximation(SEA)frame.The circularly polarized laser fields are chosen.Diffraction pattern in the photoelectron distributions is induced by a soft X-ray circularly polarized laser at?=5 nm.For comparison,we present the PMD and PAD by an XUV laser pulse at?=30 nm,it is also found that changing the sign of the helicity will lead to the rotation of the PMD and PAD.Besides,we also present the PMD and PAD in both parallel and perpendicular linearly polarized laser fields at?=30 nm.The results show that the PMD in the circularly polarized laser fields are superpositions of the PMD for the linearly parallel and perpendicular polarized cases.