Design and sol–gel preparation of a six-layer tri-wavelength ORMOSIL antireflective coating for a high power laser system

A six-layer tri-wavelength antireflective (TWAR) coating possessing nearly 100% transmittance simultaneously at 1064 nm, 532 nm and 355 nm was designed and realized by a simple sol–gel process. This TWAR coating consisted of six alternating layers of two quarterwave low refractive index components. The refractive indices of these two these two components are 1.21 and 1.14. Organically modified silicate (ORMOSIL) thin films with a refractive index of 1.21–1.13 were prepared by using tetramethylorthosilicate (TEOS) and dimethyldiethoxysilane (DDS) as co-precursors. A discussion of the crack problem on the interfaces of the multi-layer sol–gel silica AR coating was proposed, which was very important in the preparation of the multi-layer AR coating with high transmittance. Finally, the designed six-layer ORMOSIL TWAR coating was realized with a transmittance of 99.7%, 99.5% and 99.2% at 355 nm, 532 nm and 1064 nm, respectively. This is the best TWAR coating so far and will find great application in a high power laser system.