The Theoretical Study Of Solids High-order Harmonic Generation And Spectral Redshift In Intense Laser Fields

With the laser coming into the human life,the word "non-linear" also comes along,one of the famous phenomena is the high-order harmonic generation(HHG)which caused by the interaction between the laser and targets.A plenty of studies have proved that the high-order harmonic generation has a wide range of applications,such as it can be used to obtain attosecond pulse and X-ray light source,and then used to observe the microstructure of the material and track the ultrafast dynamic process of electrons in the material.So it becomes a topical issue both in experiment and in theoretical calculation.People apply oneself to the study of gas HHG during the past three decades.Although it has achieved great success,the exploration of science is endless.Then people moved their eyes from gas target medium transfer to solid target medium.There is a big gap of the electron density between the solid and gas target,coupled with the periodicity of solid medium,which make the HHG of the former more efficiency.So the study on HHG of solid has become a subject of extensive exploration.Main contents of our researches are as following aspects:The HHG of doped semiconductor is researched.We perform that the energy band splitting occurs in the doped semiconductor,and the interval of band splitting can be controlled by adjusting the depth of the potential well.In addition,we show that the second plateau of the HHG can be enhanced in the doped semiconductor than that in the intrinsic semiconductor.As the influence of different amount of impurities on energy band splitting is considered,it is found that the impurity energy level evolves into impurity energy band by adding a series of impurities,which lead the energy band splitting.The high-order harmonic generation with different initial states is investigated.The intensity of the second plateau of the HHG with the initial multiphoton ionization channel is higher than that with the tunneling ionization channel,and the cutoff energy of the harmonics with the initial multiphoton ionization channel is extended.We found that the electron with initial multiphoton ionization channel correspond to many abundant roads.Not only does the direct transition occur,but also indirect transition will be.We investigate the recombination process of electrons in solids by using Bohm trajectories.By comparison,it is found that the Bohm trajectories of solids are in well agreement with the time-dependent electron probability density,which demonstrates that we can use the Bohmian trajectories to study the composite processes of the electrons in solid.The solid HHG can be emission when the Bohmian trajectories reverse its direction.To further prove our point of view,the variation of the total energy obtained by the Bohm particle with time is given.It can be observed that when the direction of Bohm trajectory changes,the whole energy obtained by the Bohm speck suddenly decreases,thus losing energy generation harmonic.For solid materials with defects,we conclude that the similarity of Bohm trajectories at different initial coordinate is broken.The Bohm trajectories at this point are similar to the Bohm trajectories of atoms,concentrated near the coordinate x=0.There are many interesting transfer phenomenon for the HHG spectral in solid.We viewed the feature of redshift at the field 2.3?m.Furthermore,the intensity of the harmonic is not continuous when the laser peak strength is enhanced.When the terahertz field is superimposed as the second laser pulse,we found that the spectral red-shift is more obvious,and the spectral red-shift can also generate and disappear by regulating the relative phase of two laser pulses.