Optimizing the effect of electric-field enhancement in nodular defects

Abstract

It has been verified that a broadband high-reflection (HR) film could restrain electric-field intensity (EFI) enhancement effect in the nodular defects at normal incidence. However, it’s impossible to design an omnidirectional HR coatings to avoid the light penetration from all incident angles at oblique incidence. In this paper, the EFI enhancement is simulated by using a three-dimensional finite-difference time-domain (FDTD) code. Two types of polarizers that prevent light penetration at low and high incident angular range (IAR) are proposed to explore the influence of transmission band at different angles in the case of oblique incidence. The damage morphologies of nodules initiating from different diameter silica microspheres in polarizers reproduce the simulated EFI distributions very well. These results indicate that light penetration at high IAR rather than at low IAR contributes mostly to EFI enhancement. Then, the conclusion is proved further by the films with low and high IAR at normal incidence. Controlling the angle position of transmission band at small angle can reduce the EFI enhancement in the usual case and increase the laser-induced damage threshold (LIDT) of films.