Relativistically intense laser pulse

Propagation in a medium of a coherent optical wave packet whose longitudinal and transverse sizes are both of a few wavelength and whose field amplitude can induce relativistic motion of electrons is a novel challenging topic to be investigated in the general field of the so-called relativistic optics [11]. Theory and simulation have been applied to this problem for a few decades. A number of experiments have been performed since ultrashort intense laser pulses became available in many laboratories. 

In this chapter we have reported on theoretical investigations of two different regimes of interaction between ultraintense EM radiation and plasmas, as examples of the application of the theoretical models developed in a previous chapter. First, we have studied the existence of localized spatial distributions of EM radiation, which appear in numerical simulations as a result of the injection of an ultrashort and intense laser pulse into an underdense plasma. Such solitonic structures originating from the equilibrium between the EM radiation pressure, the plasma pressure and the ambipolar field associated with the space charge have been described in the framework of both a relativistic kinetic model and a relativistic fluid approach. It has also been shown that... 

Figure 1.1 Electron current density as a function of time. The laser pulse is characterized by a frequency co = 27.21 eV and an intensity I = 3.51 x 1021 W cm-2 = 105 a.u. Nonrelativistic (left part) and relativistic (right part) results are shown.

Leaving aside the important problem of interaction between ultrahigh-intensity femtosecond laser pulses and relativistic electrons, we shall consider below only the effects involved in the control of non relativistic electrons, such as coherent diffraction, deflection, focusing, and reflection. The diffraction of an electron beam by a standing light wave (the Kapitza-Dirac effect, Kapitza and Dirac 1933) is essentially the earliest proposal for the control of matter by light. 

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