Enhance anti-water ability of high transmittance film in mid-infrared band

In order to obtain high-performance short-mid infrared anti-reflection membrane, Si, SiO, and MgF2 are used to design the system structure, in which MgF2 is located in the outermost layer and expose in the atmosphere. However, due to the porous structure of fluoride thin film, the peaking density of MgF2 film is low, which is prone to the moisture absorbing. The water vapor comes into the film not only caused the transmittance decrease but also lead to the poor adhesion. The excessive power of ion source assisted deposition increases the stress of MgF2 film, resulting in the stress mismatch between MgF2 film and the previous Si layer, caused the MgF2 film cracks. To improve the adhesion of the film, this paper invests a way to matching stress by plating bond layer between MgF2 and Si, and adopts the step annealing process combined with ion beam assisted deposition to improve the film aggregation density and decrease the absorption of water vapor, and further reduce the film stress. The spectral transmittance of prepared films is greater than 96% in1.5~5μm. After 7 days, the spectral transmittance decreased by only 0.6% and remained stable for the next 30 days. The prepared film with high quality can through 10 times adhesive test without fracture.