Fig. 1. Theoretical model of monolayer film and the relationship between optical density and film thickness

Fig. 2. The layered coating process

Fig. 3. Etching of two ion source

Fig. 4. High precision neutral density filter with multistep

Fig. 5. The etching of Ni and Cr thin films under two ion sources

Fig. 6. Surface morphology changes of the film under different etching conditions