Diffraction modelling of laser ablation using transmission masks

We present an analysis of near-field diffraction effects in ablation with transmission masks, based on coupling a simplified form of the Fresnel–Kirchhoff diffraction integral with basic models for material removal. Modelling for square, hexagonal and circular proximity masks is described and compared with previously reported experiments on glass, silicon and polyimide using excimer, femtosecond and CO₂ lasers. The model has general applicability and can provide useful insight into the effect of near-field diffraction in ablation patterning.