Femtosecond Laser Fabrication and Ultrafast Dynamics Study on FTO Film

Transparent conductive oxides (TCO) are widely used in optoelectronic devices due to their high visible light transmittance and high electrical conductivity. Fabricating micro-nano structures on TCO films with femtosecond lasers can further enhance their optoelectronic properties. However, most of the existing researches on femtosecond laser processing of TCO films focus on materials such as indium tin oxide (ITO) and ZnO, and the research on fluorine-doped tin oxide (FTO) is still insufficient. In this paper, the ablation rules of FTO film irradiated by femtosecond laser is studied in detail. When the fluence is reduced to 1/e2 of the peak value as the radius of the laser spot, the ablation threshold measured by epitaxy method is 1.27 J/cm2. The experiment explores the ablation morphology of FTO film irradiated by single femtosecond laser pulse. When the laser fluence is 2.8-8.3 J/cm2, a bowl-shaped micro-crater is ablated, and when the laser fluence is 9.6-23.4 J/cm2, a secondary crater with a vertical inner wall and a flat bottom generates in the center of the ablated bowl-shaped crater. The pump-probe technique was used to study the ultrafast dynamics of the femtosecond laser interaction with FTO film, and we found that the phase explosion was responsible for the bowl-shaped crater formation.