Self-defocusing of super-Gaussian laser beam in tunnel ionized plasmas

Based on moment theory, an analytical formalism of high intensity super-Gaussian laser beam propagation through a tunnel ionized gas is developed by including the effects of diffraction divergence and nonlinear refraction. During the interaction of the laser with the plasma, the plasma density is found to have a broad maximum on the axis in the direction of propagation of the laser, causing self defocusing of the laser beam. It is seen that the super-Gaussian beam suffers stronger divergence than a Gaussian beam. The laser beam is found to get more defocused for the cases of higher intensity and smaller spot size of the laser. For in depth study, the calculations are carried out for argon, neon and xenon gases and it is seen that different gases lead to different diffraction divergence.