Interaction of Superstrong Laser Radiation with Plasma

Abstract

Interaction of superstrong laser radiation with the matter under extreme conditions in ultrashort space-time scales is of prime importance specifically connected with the problems of generation and probing of high energy-density plasma, ions acceleration and inertial confinement fusion, compact laser-plasma accelerators, production of antimatter, etc. Generally, the interaction of such fields with the electrons in the presence of a third body makes available the revelation of many nonlinear relativistic electrodynamic phenomena. As a third body can serve an ion and in the super intense laser fields one can observe relativistic above-threshold ionization and high-order harmonic generation and shortwave coherent radiation implementation, electron–positron pairs production on nuclei, and multiphoton stimulated bremsstrahlung of electrons on the ions/nuclei. The latter is one of the fundamental processes at the interaction of superstrong laser pulses with plasma and under some circumstances inverse-bremsstrahlung absorption may become dominant mechanism for absorption of strong EM radiation in plasma. Theoretical investigations regarding the plasma absorption problem on the base of inverse bremsstrahlung were carried out mainly in the Born approximation over the scattering potential, meanwhile at the ions large charge and for the clusters, when electron interaction with the entire dense cluster ion core that composed of a large number of ions is dominant, the Born approximation is not applicable. Taking into account this fact and the significance of this problem with the application of the existing already X-ray free-electron lasers, the description of this chapter, we will start from the presentation of the quantum theory of the inverse-bremsstrahlung absorption with the exact consideration of the scattering Coulomb potential, which at first allows to develop analytical theory for absorption process in the plasma at the exact description of electrons interaction with the static scattering field, and second—will describe the quantum contribution into the plasma absorption rate at the high X-ray frequencies. Regarding the multiphoton absorption of superstrong laser radiation in the plasma, for the infrared and optical lasers one can apply classical theory, and the main approximation in the classical theory is the low-frequency or impact approximation. Then, we will present the nonlinear theory of the absorption of super intense radiation of relativistic and asymptotically large intensities in the isotropic and anisotropic classical as well as quantum plasmas due to the inverse-bremsstrahlung absorption, taking into account the initial relativism of the plasma electrons in such superstrong fields.