Design and Synthesis of Neutral Density Filter in Visible Range for Color Sorting Applications

This paper provides the design, construction, and characterization of a neutral density filter (NDF) for the visible spectrum and investigate the thickness effect on their various properties. In this work, Nichrome single layer was designed by the Essential Macleod modelling software. The Co-evaporation ofss nickel and chromium was used to construct a filter on a glass substrate by thermal vacuum coating unit under high vacuum. Low thickness supports amorphous nature examined by XRD diffractogram. Energy-Dispersive X-ray Spectroscopy (EDAX) examinations of the thin films revealed that high thickness has slight variation in constant stoichiometry for the chosen Nickel/Chromium ratio (80:20) during co-evaporation and confirm the deposition is successfully done. Additionally, Atomic Force Microscopy (AFM) analysis revealed that surface roughness decreased from 6.034 to 2.895 in correlation with increased layer thickness. These methods made it possible to produce NDFs with optical densities ranging from 0.5 OD at 10 nm film thickness to 2.7 OD at 70 nm thickness. As a result, for steady and long-lasting NDF, the spectral fluctuation of thin filters in our case is lowest at 10 nm (ΔOD= 0.08). A good match data was found between optical transmission and absorption spectra of the designed and the deposited films. The designed NDF's applicability and effectiveness for color sorting tasks were subsequently examined, marking a promising step towards advancing optical engineering solutions in this specific application domain.