Propagation and focusing dependency of a laser beam with its aberration distribution: understanding of the halo induced disturbance.

In various applications, it is necessary to understand laser field dynamics during its propagation, especially at the focal position including the dispersed energy surrounding the main pulse, that is called the halo effect. For instance, the properties of electron beams produced by Laser Wake Field Acceleration (LWFA) strongly depend on the laser energy distribution and its halo in the vicinity of the focus. Indeed, under certain condition this halo, or even its internal structures, can propagate and be self-focused independently of the main pulse in the plasma. This paper aims at providing sufficient tools to properly describe the behavior of a focused laser beam, including the halo. Consequently, an optical description regarding the source of this halo is provided. Therefore, a more accurate estimation of the input laser beam that should be used in simulations of high-power laser applications, may now be obtained. Finally, one may also find ways to positively manipulate the laser beam. Using Fresnel diffraction theory, the propagation and focusing of an experimental high-power (sub-petawatt) aberrated beam is numerically calculated. The shape of the focused beam pattern within a few Rayleigh lengths is analysed as a function of main aberrations (up to the 14th term of Zernike Polynomials). Furthermore, at the focus position, spreading of the energy is compared to both the case of a perfect diffraction-limited Gaussian and a super-Gaussian beam.