Mechanism of Breakdown and Plasma Evolution in Water Induced by Wide Pulse Widths of Laser Radiation: Numerical Study

Abstract

Numerical simulation‏ is presented to investigate the experimental results that carried out to study the breakdown of distilled water as a good emulate of the ocular tissue of the eye. The experiment used a visible laser source (580 nm) operating with pulses of width 100 fs, 30 ps, and 6.0 ns. The model solves numerically a rate equation that describes the temporal evolution of the electron density in the focal volume under the collective effect of multi-photon and‏ electron collision‏ ionization processes. Besides diffusion of electrons from the interaction region and recombination are considered as removal mechanisms. The model is validated by carrying out the calculations to obtain first a comparison between the threshold intensity as a function of the pulse width and the experimentally measured ones. Secondly, a detailed investigation of the physical processes which contribute to water breakdown connected with each laser pulse width is performed. This study is fulfilled by the determination of; the temporal evolution of the electron density at the center of the focal volume and along its radial and axial distances. The results also presented the localized distribution of the electron density in the formed plasma and its surrounded ionization regions. Finally, the effect of laser power on the linearity of the medium at the interaction region is examined for the three laser pulses to clarify the role of the self-focusing phenomenon.