Investigation On Theoretical Models And Their Applications For High Harmonic Generation In Strong Laser Fields

High harmonic generation in the interaction between strong laser field and materials is one of the basis phenomena in attosecond physics.High harmonic generation paves the way to achieving the extreme ultraviolet attosecond(1 attosecond~?second)coherent light source.The attosecond metrology based on harmonic spectrum and attosecond pulses provide an essential tool for investigating the ultrafast electron dynamics in materials,and take a deeper insight into the corresponding physical mechanism.In this paper,we study the high harmonic generation process in the interaction between strong laser field and materials.Furthermore,we explore its applications on generation and control the attosecond pulses and measurement of the ultrafast electron dynamics.Then main contents of our works are:(1)A photon channel perspective on high harmonic generation is proposed.By quantizing both the driven laser and the harmonics,the harmonic yield can be expressed as a sum of the contribution of all the photon channels.Our work improved the theory systems on high harmonic generation,and provided good descriptions on the photonic properties of harmonic spectra.From this perspective,the contribution of a specific photon channel follows a simple scaling law,and we predicted the competition between different channels.Moreover,we proposed a scheme for control the ellipticity of the attosecond pulses by using a bicircular field with different frequency ratios,and demonstrated that the ellipticity of attosecond pulses can reach about 0.8 in our scheme.(2)A reciprocal-space-trajectory model for high harmonic generation in solids is proposed,and a four step picture is revealed(pre-acceleration,ionization,acceleration,emission)by analyzing the quantum trajectories.By analyzing the harmonic spectra from driven laser fields with different ellipticity,we find the pre-acceleration plays an important role on high harmonic generation process,based on which,we predicted a new cutoff law and the cutoff extension phenomenon.In addition,by analyzing the electron trajectories and the time-frequency spectrogram,we show that the emission of high harmonic generation in solids cannot be interpreted in terms of the classical recollision picture alone.Instead,the radiation should be described by the electron-hole polarization currents,which leads to the unusual ellipticity dependence harmonic yields.(3)A scheme for real-time observation of Bloch oscillations in semiconductors using time-resolved band gap emission spectroscopy is proposed.By analyzing the electron trajectories,we find the band emission yield is directly connected to the time-dependent electron population in the conduction band.Based on this,we proposed the scheme for observing the Bloch oscillation in real time.the dynamics Bloch oscillation can be probed by measuring the band gap emission signal versus pump-probe delay.By using our scheme,one can not only track the electron Bloch oscillations driven by the pump lasers,but also one can determine the occurrence time and location of the Bragg reflections when the pump laser is strong enough to driven the electron to the edge of the first Brillouin zone.(4)A method to reconstruct the band structure of semiconductors is proposed,by using the temporal two-slit interferometry.Based on the reciprocal-space-trajectory model,we construct a temporal interferometry in the high harmonic generation process,and the corresponding interference fringe is the harmonic spectrum.Based on the relation between the band structure and interference fringe,one can retrieve the electron band structure from the harmonic spectrum with a few-cycle laser pulse.Our scheme has time resolution of femtosecond,and paves the way to track the ultrafast modification of band structure.