Analysis of thickness influence on refractive index and absorption coefficient of zinc selenide thin films.

Abstract

Linear optical constants of thermally evaporated Zinc Selenide thin films are computed on the account of only transmittance experimental data. The refractive index and absorption coefficient dispersions of Zinc Selenide layers of small to close-to-bulk (50 nm ÷ 800 nm) thicknesses deposited on transparent quartz substrates are reckoned over a broad wavelength spectrum (300 nm ÷ 2500 nm). To distinct optical thickness classes, distinct analytical approach methods are implemented to compute the refractive index dispersions (Sellmeier equations) and absorption coefficient values, with the substrate's influence accounted for. The implemented methods are exploited to infer the linear optical constants for practically any thin film thickness, with the premise that all considered films are deposited by a same deposition method. Although different deposition methods may lead to different thickness dependencies of the linear optical constants (thin films of the same material having to be regarded accordingly to the deposition process), the implemented approach stays. The study substantiates the possibility and uplifts the importance of prior knowledge on thickness dependent linear optical constants to design thin film structures with particular, custom features for linear and nonlinear photonics applications.