Research On The Temporal And Spatial Characteristics Of High-order Harmonics Driven By A Strong Laser Field

The interaction between the strong laser pulse and medium has been drawn considerable attention.Among mentioned above,high-order harmonic generation from nonlinear gas by super intense impulse in nonlinear gas is the most attractive scheme to generate the ultraviolet coherent light source,and is also the major choice to achieve the attosecond pulse so far.In this thesis,we numerically analyze the microscopic process of high-order harmonic generation by high-power laser pulse and the macroscopic propagation of high-order harmonic in the medium.The isolated attosecond pulses are synthesized via the two-color field scheme and factors affecting the spatial distribution in the far-field were studied.Point one concentrates on the microscopic physical process of high order harmonic generation by the interaction between the strong laser field and the gaseous medium.Firstly,on the aspect of classical dynamic,we apply classical three-step model to explain the process of high harmonic generation under the single frequency pulse.Then,the electron beam function describing the complete motion of electrons in the laser field is numerically solved by the time-dependent Schrodinger equation and the high-order harmonic spectrum is calculated.Finally,the Morlet wavelet transform is used to analyze the radiation of high order harmonics.The two-color field scheme is adopted to improve high-order harmonic generation compared to single frequency pulse.An isolated attosecond pulse with a pulse width of 52 as is successfully obtained.Point two concentrates on the macroscopic propagation process of high-order harmonics generation by an intense laser pulse in a gas eous medium is studied in the gas medium.Based on Maxwell's equations,the active wave equation for the propagation of high-order harmonic is derived,and the nonlinear polarization response of the gaseous medium is calculated as the source term in the wave equation of macroscopic propagation.We numerically solve the wave equation to simulate the propagation process of high-order harmonic in the gas medium,and analyze the influence of different spatial distribution of laser pulse,focusing position and location of air chamber on the propagation of high-order harmonic.