Control Of Electron-multirescattering For Ultrashort Attosecond Pulse Generation

Recently,the generations and applications of the attosecond pulse are the most advanced field in atom,molecule and photophysics.The time frame of the electron to orbit the nuclear is attosecond level.So we could directly use attosecond pulse to detect and manipulate the dynamic of the electron.In the experiment,the single attosecond pulse is useful to observe electron motion in real time,so that we want to obtain it.The high-order harmonic generation(HHG)have characteristics as follow.The first few orders will drop down quickly with the increasing of the energy,it's called perturbation area.Then the intensity of the harmonic will unchanged with the increasing of the orders,it's called plateau region.At the end of the plateau,the intensity of the harmonic will drop down sharply,it's called cut off region.Superpose the supercontinuum structure at the end of the plateau,we could obtain attosecond.So the HHG is the most useful method to obtain attosecond.However,the HHG are related to the long trajectory and short trajectory,we could obtain attosecond pulse train when we superpose the harmonics directly.So we want to adjust the dynamic process of the interaction of the laser field and atoms to obtain isolated attosecond pulse.According to the semiclassical tree-step model,the electron could recollision with the nuclear more than one time,and every time it will emit radiation.So the multirescattering phenomenon of the electron is not useful to obtain attosecond.We have to control the multirescattering phenomenon of the electron to obtain supercontinuum HHG.So that we could easier to get ultra-short isolated attosecond.The purpose of this paper is to gain an ultra-short attosecond by control the multirescattering of the electron.We used the pseudospectral method to numerically compute the time-dependent Schr?dinger equation(TDSE)of the 3-dimensional Helium atom interaction with mid-infrared laser field or mid-infrared and extreme ultraviolet compound laser field.And then we can research the spectra of the HHG.The research shows that in the Mid-infrared and Extreme ultraviolet compound laser field,the harmonic in the plateau region generated by Mid-infrared and Extreme ultraviolet laser field have little oscillation.So that we could obtain ultra-wide band supercontinuum spectrum.In addition,when we contrast the time-frequency analysis plot of these two kinds of laser field.We found that when we add the extreme ultraviolet laser field,the harmonic emitted more concentrate and more smoothly and the intense of the harmonic generation have been increased.That means the multirescattering of are suppressed.What's more,we could also found the contribution of the long trajectory is smaller.Combine the above analysis,we illuminate why the harmonic oscillation of the plateau region are suppressed.The resultant shows that in the Mid-infrared and Extreme ultraviolet compound laser field(the frequency of the XUV is the energy level difference between 1s state to 2p state of Helium atom),the multirescattering of the electron are suppressed by means of the XUV field with appropriate time delay.So that we obtain an isolated attosecond with 21 as FWHM.