Electric-field intensity enhancement of a series of artificial nodules in a broadband high-reflection coating

Abstract

A broadband high-reflection (HR) coating was used to suppress the electric-field intensity (EFI) enhancement in artificial nodules with five different sizes. However, the finitie-difference time-domain simulations reflected that the nodules initiating from 1.0-μmSiO2 seeds showed abnormally stronger EFI enhancement, which is almost two times higher than the EFI enhancement of 1.0-μmSiO2 seeds in a quarter-wave HR coating. This was also confirmed by the laser-induced damage threshold measurement. Our previous model combining light focusing and light penetrating effects was carefully examined to check whether the hotspots in a nodule initiating from the 1.0-μmSiO2 seed were in the focal area or not. Although it was found that the focal length of the nodule decreased with reducing seed diameter, the hotspots in nodules initiating from a 1.0-μmSiO2 seed were still much shallower than the focal area. In the broadband HR coating, the standing-wave EFI profiles at different working angles were given, which showed that the standing-wave EFI at the hotspots region was not negligible. Some complex interference or diffraction may cause the light to arrive at the hotspots region in phase and result in strong EFI enhancement. More work is necessary to gain a deeper understanding of this phenomenon.