Study On Generation And Characteristic Of Attosecond Pulse In Laser Plasma Interaction

The research and development of laser technology is becoming more and more mature,and it is continuously improved to meet the needs of various performances.In the field of laser technology,the Q-switching technology makes the laser pulse to the nanosecond level,and the mode-locking technology brings the laser pulse to the picosecond level.In the further development of the mode-locking technology,the door of the femtosecond level of the laser pulse is opened.Nowadays,ultrashort laser pulses with only a few optical cycles are a new technology.Its application has become a hot topic in the physics industry.Particle-In-Cell(PIC)was simulated through LPIC++program in this paper.The characteristics of Attosecond Pulse(AP)in Laser-Plasma Interaction(LPI)are studied and analyzed.In the ultrashort laser pulse,the carrier-envelope-Phase(CEP)represents the trend of the periodic variation of the field under the envelope.Once the CEP is determined,the field oscillation is determined.AP radiation of three mechanisms is generated by using the different intensities incident ultrashort laser pulse in LPI.Coherent Wake Emission(CWE)is a high-order harmonic radiation generated by linear mode conversion.Relativistic Oscillating Mirror(ROM)is attosecond pulse radiation by Doppler up-shifting after the laser is specularly reflected.Attosecond pulse is limited by Fourier transform.Coherent Synchrotron Emission(CSE)is attosecond pulse generated by the stored energy in a nano-electron beam that is effectively coupled into electromagnetic radiation.The PIC simulation of LPI process is performed by adjusting the parameters of the laser,plasma and box,and then the radiation signals of the simulation output are processed and analyzed.However,for the selection of the signal processing method,it is necessary to take into account the spatio-temporal resolution of the signal,and the resolution meets certain requirements,so that the signal can be better extracted and analyzed.The advantages and disadvantages of the six methods are analyzed in this paper.This methods are Fast Fourier Transform(FFT),Short-Time Fourier Transform(STFT),Wavelet Transform(WT),The Wigner-ville Distribution(WD),S Transform and Generalized S Transform,respectively.The generalized S transform is selected as the optimal signal processing method.After the radiation signal is processed and analyzed by generalized S transform,AP radiation is obtained in both the direction of reflection and the direction of transmission of the incident ultrashort laser pulse.Finally,the factors affecting the generation of AP radiation are analyzed.It is found that CEP has a great influence on HHG,and the spectral attenuation index of CSE-generated AP is more gradual than ROM.This characteristic indicates that the intensity of AP radiation can be further improved,which also indicates the direction for obtaining a new short-wavelength coherent radiation source.