Design And Deposition Of Infrared Antireflection Protection Film On Magnesium Fluoride Substrate For3～5μm

Magnesium fluoride as a common material for windows and fairing are widely used in3-5μm infrared range, the advantages of Magnesium fluoride are high transmittance, low dielectric constant and dielectric loss, etc. However as a substrate, due to its poor mechanical strength and physical property, it is difficult to meet the using demand of the in harsh environments, so we must deposit anti-reflection film and protective coating on its surface. In this paper, we select the H4and SiO2as the high and low refractive index materials and use the TFCalc software for film system design. After repeated experiment, SiO2will appear absorption at the band of infrared. We get the ideal design film system by using MgF2and SiO2as the low-index materials to redesign and optimize to reduce the absorption. DLC (diamond-like carbon) protection coating is deposited by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). Through contrast tests, the best deposition process is obtained by setting deposition time as invariant, the reaction gas flow rate and deposition temperature as variables. Meanwhile the problem of associativity between antireflection film and DLC protection coating is solved by adding a transition layer. The result shows that the average transmittance of this film in3～5μm is95.5%, and this film can withstands harsh environment tests.