Spectral Characteristics And Dynamics Induced By The Few-cycle Intense Laser Fields In Solid High-order Harmonic Generation

With the development of laser technology,the laser-matter interaction produces a series of new nonlinear optical phenomena,such as high-order harmonic generation(HHG),it has become an important research field in ultrafast physics.HHG in atomic and molecular systems has been well applied,however,the lower harmonic yields in atomic and molecular systems are a relatively obvious disadvantage.HHG in solids has attracted extensive attention because of the higher harmonic yields compared with the atomic and molecular systems.HHG in solids driven by intensity laser field has opened a new front edge of strongfield physics.In exploring HHG in solids,the single-electron model based on energy-band theory can better help us to understand the dynamics.We can also divide the single-electron model into single-band model and multi-band model to study the mechanism of HHG in solids.The time scale of HHG in atomic and molecular systems is attosecond,and a large number of theoretical and experimental studies have shown the results of subcycle spectral structures and dynamics in atomic and molecular systems.However,the time scale of HHG dynamics in solids is sub-femtosecond,and the dynamic process driven by subcycle laser pulses needs to be explored.Based on single-band model and multi-band model,we have explored the generation of solid high-order harmonics in this paper.For the single band model,we have realized the direct measurement of band structure from HHG based on NEWUOA,a derivative-free unconstrained optimization algorithm.The sensitivity of HHG in solids to band structure is obtained from one dimensional single band model.In addition,we have analyzed the HHG oscillation structure and dynamics of single-band model.For the multi-band model,we have numerically calculated the band structure based on the Mathieu-Type model potential and solved the time-dependent Schr?dinger equation based on the Bloch basis in the velocity gauge.Firstly,we have studied the multi-plateau HHG in solids,and then we have expanded the oscillation structure to multi-band model.We have calculated the relationship between HHG and time delay.The results have shown that HHG spectrum in solids appears more complex oscillation mode than in atomic and molecular systems.However,in different model systems,we have observed the enhancement or suppression of HHG related to subcycle laser pulses from HHG spectrum.In order to better understand the correlation between the oscillating structure and the subcycle laser pulse,the time-frequency analysis method and the probability density distribution of HHG radiation are used to analyze the dynamics under the specific time delay in detail.