Study On The Isolated Attosecond Pulse Generation From The Orthogonally Polarized Gating Scheme

High-order harmonic generation is currently the only effective method to obtain X-ray attosecond pulse in the table due to its unique platform structure and equal frequency distribution characteristics.Taking into account the limitations of traditional polarization gating schemes in obtaining attosecond pulses,in this dissertation,we propose the orthogonally polarized gating scheme by two perpendicular to each other delayed linearly polarized pulses and a dual optical gating scheme based on the above scheme.Subsequently,the high-order harmonic and attosecond pulse generation by helium atom with the two schemes were explored.The main contents of this paper are as follows:1.By using Lewenstein’s strong field approximation model theory,we numerically simulate the high-order harmonic and the isolated attosecond pulse from helium atom irradiated by an orthogonally polarized field,which is consist of two 4-femtosecond linear polarization pulses with orthogonally polarized directions.It is found that when the time delay between two linearly polarized pulses is 1.25 optical periods,a continuous harmonic spectrum ranging from 190 th to 290 th is obtained.Compared with the harmonic spectrum from helium atom irradiated by a single linear polarization pulse under the same condition,the super-continuum plateau in the former is wider.By superimposing the super-continuous harmonic,an isolated short pulse with 108 attosecond is obtained.2.Based on the orthogonally polarized field,we further simulated the high-order harmonic generation and attosecond pulse by helium atom interacting with a dual field composed of the above orthogonally polarized field and a second harmonic pulse.The purpose of adding a second harmonic pulse in the driving pulse direction is to obtain high-order harmonic generation with higher supercontinuum bandwidth and efficiency than before by adjusting the amplitude difference between two adjacent half optical periods.At first,the dual field is consist of the 4-femtosecond orthogonally polarized with a second harmonic.A better high-order harmonic spectrum can be obtained by adjusting reasonably the time delay and the phase of the pulse.The isolated short pulse of 143 attosecond will be obtained after Fourier transform.In order to further relax the requirements of the incident driving pulse,we also use a dual optical gating pulse with a 7-femtosecond pulse width,and similarly obtain a high-order harmonic emission spectrum with high efficiency and broadband supercontinuum bandwidth.An isolated short pulse of 124 attoseconds is obtained After Fourier transform.Compared with the traditional dual-optical gating scheme,our scheme is not only easier to operate in the experiment,but also overcomes the limitation of the pulse-width and intensity of the incident pulse.Furthermore,it also avoids the atomic pre-ionization which is not conducive to the harmonic phase matching in traditional scheme.