Research On Attosecond Pulse Generation And Optimization With The Chirped Two-color Laser Field

Interaction of laser with molecular and atoms has been studied extensively in the past years.Attosecond pulses can serve as a robust tool for accessing the electron dynamics in atoms,molecules and materials,such as atomic photoexcitation and photoionization,electron–electron and electron–nucleus correlations and electronic dynamics in nanosystems.Thus far,high-order harmonic generation?HHG?,known as anonpertubative,highly nonlinear process and Special spectrum features,has been the unique way to produce attosecond pulses in experiments.This paper focuses on the evolution of H₂⁺in laser field and how to obtain the IAP,and to control and optimization of the IAP,and propose a new scheme of obtaining the IAP,in order to obtain more efficient IAP light source.The main contents of this paper are as follows:?1?The radiation process of the harmonic generated by the interaction between the laser and the molecular atom is analyzed theoretically.Firstly,the classical theoretical model,the strong field approximation theory and the numerical solution of the time-dependent Schrodinger equation are introduced in this paper.Then,the propagation process of high-order harmonics in macroscopic media and the corresponding simulation model are introduced in detail.These models provide the theoretical basis for the acquisition of high-order harmonics and attosecond pulses.?2?The evolution of H₂⁺in the laser field is studied by using the time-dependent Schrodinger equation under the condition of Bonn-Oppenheimer.The transition between the ground state of H₂⁺and the second excited state is compared with the laser field of800 nm and 138 nm,respectively.It was found that electrons were more prone to transition between low energy levels and high energy levels at 138 nm wavelengths.Then,the change of nuclear distance and ionization rate of H₂⁺with time under laser field was studied.The results show that,under the action of the 800 nm laser field,H₂⁺only makes periodic vibrations near the equilibrium kernel spacing.At different times to join the extreme ultraviolet light source can control H₂⁺ionization.In the vibrational state of charge resonance enhanced ionization,the initial average kernel spacing of the molecule is the largest.?3?The process of generating of high-order harmonics and IAP between the laser and the neno atom is studied.In the process of single atom response,the generation of high-order harmonics under the driving of laser field with multicycle 800nm and 1300nm synthesis was studied.It is found that in the multicycle two-color field driven,near the cut-off area can produce a section of supercontinuum.On the basis of this,the influence of different control field parameters on the IAP is studied in the process of single-atom response.It is found that the simple two-color field scheme without chirp can not produce IAP when the pulse width reaches 40 femtosecond.The study of the control field parameters provides a prerequisite for the selection of the chirped two-color field parameters.?4?A new scheme for generating IAP by chirped two-color laser field driven is proposed and the influence of control field parameters on the generation of IAP is studied.In the same pulse width of 40fs two-color laser field driven,by contrasting the high-order harmonics and the generation of the IAP,in the fundamental pulse to join the chirp and no chirp.It is found that the IAP cannot be generated by the two-color field without chirp,and the IAP can be obtained by chirped two-color field.On this basis,the influence of the control field parameters on the IAP is studied.The results show that in our scheme,an IAP can be generated even without carrier envelop phase?CEP?stabilization.Such a CEP-unstablized multicycle pulse can be easily obtained in most laser laboratories.