Crack Suppression of Transparent Protective Layer on Polycarbonate Formed by Fluorine Laser

A transparent, hard silica glass SiO2 layer was formed on a conventional protective coat made of silicone [SiOCH32]n on a polycarbonate plate by the 157 nm fluorine F2 laser-induced photochemical modification of silicone into SiO2. Long exposure of the F2 laser to the sample produced cracks on the surface; a metallic mesh mask was set on the sample during F2 laser irradiation to suppress the cracks successfully. As a result, the thickness of the formed SiO2 layer could increase to approximately 1.3 µm without any crack, and the hardness of the sample also increased to approximately 2.8 GPa.