Complex Recollision Dynamics Analysis Of High-order Harmonic Generation In Solids

The generation of high-order harmonics has greatly promoted the research and development of ultrafast optics and even the entire physics.It not only provides us with a means to detect electronic dynamics by synthesizing isolated attosecond pulses,but also provides us with a new tool for understanding the microscopic world.In the past few decades,researchers have focused on the generation of high-order harmonics in gas targets.In recent years,due to the development of laser technology,people have gradually turned their attention to higher density solid materials.At present,the generation mechanism of solid harmonics is still being explored.Among them,the recollision model in real space and three-step model in k-space have achieved great success and are widely used.Moreover,these two models have been validated in different quantum models.However,it is unknown which one is more suitable for real solid environments.In addition,people have gradually realized that solid harmonics have more complicated dynamic processes than gas harmonics.But the source of this complexity is unclear.Based on the above problems,we simulated the interaction of intense lasers and solid by time-dependent density functional theory(TDDFT),and extended the recollision model in real space from two-band to multi-band to study the complicated dynamic process of solid harmonics.First,we extend the recollision model in real space from two band to the multi-band.By comparing the classic trajectories calculated by the multi-band recollision model in real space and the three-step model in k space(acceleration theory)with the time-frequency distribution of the harmonic spectrum calculated by the TDDFT,the recollision model in real space is proved to be correct.It’s also confirms that the recollision of electrons and holes in real space is one of the basic mechanisms for the generation of solid interband harmonics.Second,we study the ultrafast dynamics of solid harmonic generation before and after dynamical Bloch oscillation using the multi-band recollision model.In the analysis of ultrafast dynamics,it is found that solid harmonics have more complex dynamics than gas harmonics.This is because the velocity reversal of electrons plays an important role in the generation of solid harmonics.For atoms and molecules,electrons have only two chances to undergo the velocity reversal in one optical cycle.But for the solid harmonic generation,the probability of the velocity reversal of electrons is greatly increased.This leads to more complex quantum paths and complex electronic dynamics processes.In addition,we also study the influence of the dephasing effects on the ultrafast dynamics of solid harmonics,and find that the dephasing effects cannot significantly change the quantum path and electronic dynamics.Finally,the relationship between the harmonics order and the migration distance of the electrons is also studied by the multi-band recollision model.We find that this relationship is very complex and path-dependent.Our work has carried out a detailed analysis of the ultrafast dynamics of solid harmonics generation,providing a deeper understanding of the complex dynamics of solid harmonics,which is a prerequisite for controlling solid harmonics by manipulating the laser field in the future.