Near-field modulation of lateral cracks
横向划痕对光场调制的近场模拟

Light intensification caused by cracks in fused silica subsurface is one of main factors of laser-induced damage to optical materials. Three-dimensional finite-difference time-domain method is used to simulate parabola-section-model lateral cracks. Moreover, the relationship between light intensification and breadth-to-depth ratio R is discussed. The results show that the morphology change after acid etching is an important cause of damage mitigation. Modulation is very weak and close to each other when R is greater than 10.0 and it increases rapidly when R less than 5.0. The electric field intensity reaches a maximal value when R ranges from 1.0 to 3.0, and the maximal electric field is 4.3 V/m. The electric field intensity of more than 80% samples exceed 2 times than the incident light when R ranges from 1.0 to 3.5. Intensified area has the skin effect with depth increasing. It is demonstrated that enhanced area lying directly below the crack firstly shifts to left and right sides, then it moves to parabola-section interface and the horizontal interface. Finally, the whole subsurface will be enhanced. In addition, electric field modulation firstly increases and then decreases in the z direction when depth is large enough.