Preparation of polysiloxane coating for laser application with improved curing property based on copolymerization modification

The sol–gel method is an important process for the preparation of laser frequency conversion components, such as dihydrogen phosphate (KDP), which are often employed in high-power laser facility. Methyltriethoxysilane (MTS) precursor is a typical matrix to prepare polysiloxane under hydrolysis and polycondensation process. Further coating and curing procedure is applied to obtain desired polysiloxane coating which acts as the moisture-proof and refractive index matching layer. Subsequently, an antireflective coating is prepared over this polysiloxane coating (a bilayer coating system) to realize ultrahigh transmission at desired wavelengths. Due to the low curing temperature (limited by the phase transition temperature of KDP), current MTS-polysiloxane coating could not be completely cured and inter-coating permeation between this bilayer coating system would lead to deterioration of coating properties. Thus, copolymerization of MTS and tetraethylorthosilicate (TEOS) is adopted to fabricate the polysiloxane coating with improved curing property (denser structure and higher hardness after curing). It is found that under certain molar ratio of MTS to TEOS, the structure of modified polysiloxane coating could be effectively densified and the coating hardness increases significantly. Meanwhile, the bilayer coating system still exhibits excellent transmission, high laser-induced damage threshold as well as satisfactory moisture resistance.