High reflection films for 800nm picoseconds laser system requires broad bandwidth, which is usually about ±50nm, or even to ±70nm, and a high laser damage threshold is needed at the same time. Multilayer dielectrics using three materials Nb<sub>2</sub>O<sub>5</sub>/SiO<sub>2</sub>-HfO<sub>2</sub>/SiO<sub>2</sub> were fabricated by electron beam evaporation. Benefit from its high refractive index of Nb<sub>2</sub>O<sub>5</sub> and the high damage threshold of HfO<sub>2</sub> films, the multilayer dielectrics were prepared successfully, which have more than 99.5% reflectance within bandwidth larger than 140nm around the center wavelength of 800 nm. The laser damage characteristics of the films at 150ps, 1Hz were studied, and the damage mechanism was analyzed.
YbF<sub>3</sub> was proposed as a substitute for ThF<sub>4</sub> in anti-reflection or reflection coatings for the infrared range, and the residual stress of YbF<sub>3</sub> thin film using APS plasma ion assisted deposition(PIAD) was studied. From the results, we found the anode voltage of PIAD has a large effect on the residual stress of YbF<sub>3</sub> thin film, and the refractive index of YbF<sub>3</sub> produced with PIAD was higher than without it, with a possible reason close to packing density. Finally, we produced multi-layer reflection coating on a 260mm diameter mono-crystalline silicon substrate. Its surface contour was approximately 0.240λ (λ＝632.8nm), and the absorption was lower than 200ppm, which can satisfy the practical requirement.