Wideband Antireflection Coatings of Porous MgF2 Films by Using Glancing Angle Deposition

Seouk-Hoon Woo, Yong Jun Park, Dae-Ho Chang, K. M. A. Sobahan and Chang Kwon Hwangbo

J. Korean Phys.Soc. 51,1501 [doi: 10.3938/jkps.51.1501 | PDF Download]

In this paper, a new method to design and fabricate a wideband antireflection (AR) coating with a porous MgF$_2$ film by using glancing angle deposition (GLAD) is proposed. Various glancing angles and substrate rotations in GLAD were employed to control the refractive indices and the microstructures of MgF$_2$ films. The relationship between the refractive index and the glancing angle of MgF$_2$ films deposited by using GLAD is investigated. The results show that as the glancing angle is increased from 0$^\circ$ to 80$^\circ$, the porosity of MgF$_2$ films increases due to the shadow effects, and the effective refractive index of MgF$_2$ films drastically decreases from 1.378 to 1.185 at 550 nm. Two-layer wideband AR coatings with porous and dense MgF$_2$ films were also deposited by using GLAD. The results show that the two-layer AR coating has low and wideband reflection for wavelengths between 400 and 1200 nm and that the average reflectance is 0.38 \%. We found that porous MgF$_2$ films deposited by using GLAD at high glancing angles provide very low refractive indices, and so are very useful for wideband AR coatings.