Parametric Modulation And Electromagnetic Radiation From Ultrashort Intense Laser Pulse Plasmas

The advent of high-energy ultra-short and -intense laser pulse has greatly promoted the progress in the research of inertial confinement fusion (ICF). The proposal of the"fast ignition"concept in ICF has the investigation of ultra-short and -intense laser pulse interaction with plasmas becomes a focus, for which the world power has invested substantive fund. The development fleetly in the field for the purpose of military equipment and national security has boosted the research of the elements science greatly and formed three span-new domains, intense field physics, intense field chemistry, and extreme condition creation. The fast progress for twenty years allows us coming into turn ours steps to application in the above three domains. In the interaction, the atoms in matter are inevitably ionized in such an intense laser field and the plasma is instantly formed on the matter surface. In theoretical, the plasma produced by the intense laser pulse is generally treated as fully ionized charged particle, in which interaction system the linear and nonlinear physic processes are essentially dominated by the laser electromagnetic field and the plasma electrostatic field. In the practical applications, however, the target-atom especially the high-Z atoms usually cannot be fully stripped by the pulse laser field. The partially stripped atoms (ions) have to be polarized and consequentially to form a polarization field under the intense laser field. The coupling of the polarization field associated with bound electrons, plasma electrostatic field associated with free electrons, and electromagnetic field associated with laser pulse how to modify the well-known physic results and what new phenomenons can be induced in the competition of the interaction have been attracting researchers'attention. On the other hand, plasma, as a special matter state without damage threshold, is a preferred medium for the generation of high power electromagnetic radiation by the excitation of the intense ultrashort laser pulse as well as the complex diversiform movements of the charged particles, which is one of the aims researchers seeked, especially for the terahertz (THz) source with high-power. This thesis just focused on the above interests and procured the progresses as follows:1. The group and phase velocities of an intense laser pulse propagating in the partially stripped plasma are derived. In the assumption of the photon-number conservation, the photon acceleration, self-focusing, longitudinal bunching, and the modulation instability of the laser pulse are investigated in the presence of the partially stripped atom polarization. The results show that, the self-focusing and photon acceleration of the laser pulse in the partially stripped plasma are much faster than in the fully stripped plasma, the existence of the atom polarization field results in the competition between normal and abnormal dispersions as well as the significant change in the longitudinal bunching and modulation instability of the laser pulse in the partially stripped plasma.2. Based on the dispersion relation of intense laser pulse propagating in the partially stripped plasma, the laser frequency modulation generated by the atomic ionizing process is investigated. We find that the ionizing speed of gas atom in the laser field determines the responding speed of the dielectric function as well as the modulating speed of the pulse frequency, in which the result shows the higher the laser frequency, the greater the blue-shift of the laser frequency due to the partially stripped atomic polarization.3. Starting from the Maxwell equations and hydrodynamic equations, the quasistatic magnetic field resulted from an intense laser pulse propagating through the partially stripped plasma is examined and the modification induced by the atomic polarization field to the self-generated magnetic field is discussed based on the perturbation theory. The results reveal that, for the higher plasma densities and higher laser frequencies, the atomic polarization field can greatly enhance the self-generated magnetic field especially can reverse its direction which can inevitably induce the un-bunch of the hot electron beam as well as be of disadvantage to the fast ignition of hot electron in the ICF.4. According to the d'Alembert equation, the possibility of THz radiation excited by an ultrashort laser pulse driven the plasma current is proved and the generation condition of the THz radiation is found in theory. The result indicates that the higher power THz radiation can occur when the group velocity of the laser pulse is greater than the phase velocity of the radiated wave and the frequency of the radiated wave approximates the reciprocal of the pulse duration.5. Based on the dielectric function of plasma in an intense laser pulse, we foretell another generation mechanism of THz radiation in theory, which results from the Cherenkov effect induced by the laser generated fast electron. The result shows that the stronger Cherenkov type THz radiation can emitted if the velocity of the fast electron slightly less than the group velocity of the laser pulse.The innovative progress in this thesis shows as follows:1. The significant modification of the partially stripped atomic polarization field to the self-generated quasistatic magnetic field is revealed and the direction of the magnetic field can be changed by the atomic polarization field, which is firstly exposed.2. The contribution of the atomic polarization field to modulate the parameters of laser pulse is uncovered.3. High power THz electromagnetic radiation by intense laser pulse interaction with plasma is predicted in theory and the condition that THz radiation occurs is presented.