The Generation Of Attosecond Pulse From The Interaction Of Laser Pulses With Plasmas

This thesis is devoted to studying three issues using the theory and one-dimensional particle simulation methods. First, we optimized the generation of attosecond pulses due to the interaction of a short ultrarelativistic laser pulse with overdense plasma, and studied the impact of the incident laser on the plasma electronic behavior and the high harmonic generation. Then the influence of laser parameters to the attosecond pulses generation using time-dependent polarization method is studied, and we got a"single"ultra-strong attosecond pulse. At last, through the comparision of the normal incidence and oblique incidence of laser pulses, we found that the number of attosecond pulses for the oblique incident laser pulse is less than the normal incidence, and gave a reasonable explanation to this phenomenon.Using one-dimensional particle-in-cell simulations, the generation of attosecond pulses is studied due to the interaction of a short ultrarelativistic laser pulse with overdense plasma. According to the ultrarelativistic similarity theory, we analyze the moving of the electrons and the generation of high-order harmonics. We find that when the plasma density is constant and with the dimensionless similarity parameter S decreased, the conversion ratio of attosecond pulses is increased at first and then decreased. So we can choose a laser pulse with appropriate intensity to get an attosecond pulse with high conversion ratio. Furthermore, when S is invariable, with the increase of the plasma density, the conversion ratio of attosecond pulses shows an upward tendency. This implies that we can get a higher attosecond pulse when a laser with suited intensity is incident on more dense plasma.The influence of time-dependent polarization to the attosecond pulses generation from the overdense plasma surface driven by laser pulse is discussed analytically and numerically. We show that the frequency of controlling pulse controls the number and the interval of the generated attosecond pulse, the generation moment of the attosecond pulse is dominated by the phase difference between controlling and driving pulse and the amplitude of the controlling pulse affects the intensity of the attosecond pulse. Using the method of time-dependent polarization, a"single"ultra-strong attosecond pulse with durationτ≈8.6as and intensity I≈3 .08×10²⁰Wcm² can be generated.At last, using one-dimensional particle-in-cell simulations, the generation of attosecond pulses is studied, which is obtained through the interaction of a short oblique incident laser pulse with overdense plasma. It is observed that the intensity and conversion ratio of attosecond pulses at oblique incidence is always higher than the normal incidence at the same parameters. And the number of attosecond pulses for the oblique incident laser pulse is only one half of the normal incidence. According to the oscillating mirror model and the equation of the mirror motion, we analysed the reason of these questions. Furthermore, when the density of plasma is invariable and the intensity of the laser pulse is raised, with the increase the times of filtering, the conversion efficiency of attosecond pulses for the oblique and normal incidence shows an approaching tendency. After selecting harmonics above the order of 300, then we can get the attosecond pulses that have reached the X-ray region. The thesis is organized as follows. The first chapter gives a brief introduction of developing process of laser technique, the interaction of laser pulse with plasma and the generation of high-order harmonics and attosecond pulses. In the second chapter, we show the theoretical model of harmonics generation from the interaction of laser pulse with atom, molecule and plasma respectively. Then, in the third chapter, the optimization of attosecond pulses from the interaction of ultrarelativistic laser with overdense plasma is explored. Chapter four presents the generation of single attosecond pulse from the overdense plasma surface driven by laser pulse with time-dependent polarization method. In the five chapter, the generation of attosecond pulses from the interaction of oblique incident laser pulse with overdense plasma is showed. As the conclusion, in the last chapter, we briefly summarize the total subject and give an expectation for the future work.