Thin film enabling sub-250 nm nano-ripples on glass by low fluence IR picosecond laser irradiation

Well-aligned parallel nanoripples, with spacing down to 250 nm, were engraved on a glass surface at a fluence 8 times less than the ablation threshold of glass using IR (λ = 1032 nm) picosecond laser system with a pulse duration of 10 ps. The glass surface was first coated with 175 nm ITO thin film prior to laser scanning. The nano-ripples were formed on the underlying glass surface during the selective removal of ITO thin film using substantially less fluence than that required without ITO on the glass surface. The laser scan speed and repetition rate determine the spatial overlapping of pulses (shots per area, SPA); this greatly influences the symmetry, spacing, and depth of the ripples achieved. The fluence ranging from 1.13 to 1.56 J cm−2 at scanning speed of 0.5 ms−1, 25 SPA, 96% overlapping at laser repetition of 400 kHz was found to be the optimal laser parameters for generating nano-ripples with 0.25λ periodicity on large area glass surface. The process offers the opportunity for gratings to be integrated in structures consisting of transparent conductive materials.