Multilayer dielectric grating pillar-removal damage induced by a picosecond laser

Multilayer dielectric gratings typically remove multiple-grating pillars after picosecond laser irradiation;however,the dynamic formation process of the removal is still unclear.In this study,the damage morphologies of multilayer dielectric gratings induced by an 8.6-ps laser pulse were closely examined.The damage included the removal of a single grating pillar and consecutive adjacent grating pillars and did not involve the destruction of the internal high-reflection mirror structure.Comparative analysis of the two damage morphological characteristics indicated the removal of adjacent pillars was related to an impact process caused by the eruption of localized materials from the left-hand pillar,exerting impact pressure on its adjacent pillars and eventually resulting in multiple pillar removal.A finite-element strain model was used to calculate the stress distribution of the grating after impact.According to the electric field distribution,the eruptive pressure of the dielectric materials after ionization was also simulated.The results suggest that the eruptive pressure resulted in a stress concentration at the root of the adjacent pillar that was sufficient to cause damage,corresponding to the experimental removal of the adjacent pillar from the root.This study provides further understanding of the laser-induced damage behavior of grating pillars and some insights into reducing the undesirable damage process for practical applications.