Study Of Attosecond Pulse Generation From Relativistic Electron Sheets

The advent of attosecond light pulses has led to the direct study of ultrafast electron dynamics in atoms,molecules and solids.Currently,the conventional method to obtain attosecond pulses is by high-harmonic generation(HHG)in gases.However,this HHG source has a low intensity and conversion efficiency,which limits attosecond research of some ultrafast processes.Recently,a new scheme on generating attosecond pulses based on isolated relativistic electron sheets has been proposed.When a relativistically intense laser impinges on the sheet,nonlinear coherent Thomson scattering(CTS)occurs.Due to the relativistic Doppler effect,the scattered pulse has a dramatically up-shifted frequency,and meanwhile its duration is compressed to the order of attosecond.This novel attosecond source possesses the merits of short pulse duration and high intensity.However,the theory is still immature and some related physical processes remains unclear.In this thesis,we study many aspects of the CTS attosecond source by theoretical analyses and particle-in-cell(PIC)simulations.The main content and results are listed as following:In the first part,we investigate the nonlinear coherent Thomson scattering of single-cycle lasers and find two new nonadiabatic effects in this regime:amplitude enhancement and frequency downshift.When the electron sheet is thicker than the wavelength of the produced attosecond pulse,these effects can increase the scattering efficiency by more than 100 times.A new analytic model is developed to explain these two effects and agrees well with PIC simulation.In the second part,a novel scheme for generating a pair of attosecond pulses by nonlinear coherent Thomson scattering has been proposed.When the laser intensity is greater than a certain threshold,the scattered signal can have a saddle-like profile with two peaks in the temporal domain.Strikingly,the lower frequency components are found to be mostly located between the two peaks.By filtering out the low-frequency part,we can obtain two attoseond pulses.The duration of each pulse can be shorter than 10 as,and their interval is flexibly tunable within 1 fs.This scheme delivers much shorter and stronger attosecond-pulse pairs than any other approaches,such as HHG.Thus,it is expected to boost the pump probe technique to an unprecedented time resolution.The study in this thesis has deepened our understanding of the coherent nonlinear interaction of laser and electron sheets in the relativistic regime.Our obtained results are very helpful for developing more intense and shorter attosecond pusles.