Modeling of ultrashort pulsed laser ablation in water and biological tissues in cylindrical coordinates

Abstract

A numerical model combining the ultrafast radiative transfer and the ablation rate equation is proposed to investigate the transient process of plasma formation during laser plasma-mediated ablation of absorbing-scattering media. The focus beam propagation governed by the transient equation of radiative transfer is solved by the transient discrete ordinates method to account for scattering effect. The temporal evolution of the free-electron density governed by the ablation rate equation is calculated using a fourth-order Runge–Kutta method to examine various effects such as the multiphoton, chromophore, and cascade ionizations. The threshold of optical breakdown, the shape and maximum length of plasma growth for ablation in water are predicted by the present model and compared with the existing experimental and numerical data. Good agreements have been found. The dynamic process of plasma formation for ablation in the model skin tissue is simulated. A parametric study with regard to the influences of the ionization energy and the critical free-electron density on the ablation threshold of the tissue is conducted.