Optical properties of double-layer MgF2 thin films as anti-reflective coating for optical lens
MgF2 thin films deposited by thermal evaporation are vastly applied onto glass lenses because of its transparency in the UV-Vis spectrum. In the present work, single, double and triple layers of MgF2 nanostructure have been grown on glass substrates by thermal evaporation method. The optical properties of MgF2 films in the UV-Visible spectrum has been investigated using the Metertech SP8001 UV-Vis spectrophotometer. The Morphology and topography analysis has been investigated using atomic force microscope (AFM). Atomic force microscopy analysis has detected that the double layer MgF2 has the lowest root mean square (1.91) nm, lowest surface roughness average (1.49) nm and the smallest grain size (21.63) nm. The optical measurements have observed that the double layer MgF2 revealed the highest transmittance in the visible region (93.3 %) at 550 nm wavelength and the lowest absorbance (0.029) and reflectance (0.066). The absorption coefficient (3395) cm-1, extinction coefficient (0.0171) and refractive index (1.31) at 550 nm wavelength for the double layer MgF2 were also the lowest among the other films. These results have proved that the double layer MgF2 film was the best among the three films for antireflection application.
Keywords: MgF2, thin film, anti-reflective, thermal evaporation, optical lenses.