Experiments on Ablation of Dielectrics on Gold, and Water

Abstract

We performed ablation on both an air-water interface and a gold-silica-air interface. Pulses with a duration of 160 fs were shot at the materials, with fluences ranging from 0.2 mJ cm^-2 up to 0.35 J cm^- 2 . This was done to study the self-reflectivity. According to existing theory the reflectivity of water should not significantly change in this fluence regime. We measure however an increase of 0.0023, around a fluence of 1 mJ cm ^-2 , after which the reflectivity stays at this constant at the higher value. When performing the measurement on the gold with a thin nano-layer of silica, we witness ablation at fluences around the ablation threshold of gold, but far below that of silica. The addition of a thin layer of silica decreases the addition with approximately 40%. Increasing the thickness of the layer will lead to an increase again of the ablation threshold. The self-reflectivity of the samples resemble those of gold, but see a steeper decline. We developed a simple model, assuming no non-linear behaviour of the silica. We will present evidence suggesting penetration of hot electrons from the gold in the silica.