Field Characteristic Of Tightly Focused Beams And Its Application In Electron Acceleration

The fast development of laser technology makes available laser pulses with peak power up to petawatt and peak light intensity up to1022W/cm2. Research on intense laser has always been emphasized due to its potential applications in such areas as scientific research, industry, medical therapy and military defence. This thesis focuses on the following two aspects:(I) Weniger Transformation method is employed to deal with divergent Lax Series;(II) Vacuum electron acceleration in radially polarized Gaussian laser beam is discussed.Lax Series method is a powerful tool to handle the electromagnetic fields of laser beams (electromagnetic fields derived from Lax Series method are called Lax fields), unfortunately, it exhibits severe divergence in non-paraxial regions for intensely focused beams. One of the original points of this thesis is that we studied the properties of general terms in detail for radially polarized Gaussian beams, and a very simple expression is found to describe phase relations between general terms of Lax Series under certain conditions. The study of general terms of Lax series justifies the choice of Weniger Transformation in a proper form (electromagnetic fields derived from Weniger Transformation are called Weniger fields). By using Fourier Transformation method, integral representations of electromagnetic fields for a radially polarized Gaussian beam are obtained as the standard fields (which satisfy Maxwell equations) to verify the validity of Weniger fields. It is found that Weniger fields provide a sound description of intensely focused radially polarized Gaussian beam, so long as the laser beam waist is larger than the wave length and the field position of interest is not too far from the focus plane of the beam. Based on the standard fields, the choice of β parameter is also briefly discussed.It has been experimentally found that a radially polarized Gaussian beam can be focused to a light spot significantly smaller than other beams, thus super intensity may be obtained for such a beam; What’s more, the symmetric distribution of the electromagnetic fields of radially poloarized Gaussian beams furnishes an ideal channel for charged particle acceleration. Therefore, another important part of this thesis was to simulate electron acceleration in Weniger fields of a radially polarized Gaussian beam, in the simulation, different initial parameters are considered (such as initial position and velocity of an electron, initial phase of the fields, etc.) and the dynamics of electrons in Weniger fields is compared in detail with that in Lax fields. Since the simulation of the motion of electrons involves the field of the whole space of a laser beam, except for special situations, the divergence of Lax fields would always give rise to illogical results for long time interaction, while Weniger fields can serve as an appropriate fields for the simulation. Finally in the thesis, we suggested a possible setup for an electron beam source based on a radially polarized Gaussian beam.