Femtosecond laser ablation of a thin silver film in air and water

In this work, single-shot craters were produced by femtosecond laser ablation using an objective with a numerical aperture NA = 0.25 and laser pulses with the 0.3-ps width and the central wavelength of 515 nm. Ablation was performed in air and distilled water. A sample, 65-nm thick silver film, was prepared by magnetron sputtering onto silica glass and crystalline silicon substrates. Craters were visualized by a scanning electron microscope. Some differences were found in the morphology of craters, depending on the substrate and on the ambient medium. A drastic increase in the crater size was observed during the ablation in water, which is explained by filamentation that occurs when the peak pulse power exceeds 1.3 MW.