Numerical investigation on the spectral reflectance characteristics of water-filled copper micropits

Water film attachment on the solid surface is a common phenomenon in engineering applications. The presence of such film significantly affects the surface spectral reflectance characteristics. The specific film geometric morphology for water-filled copper micropit is firstly constructed by Surface Evolver, and then the spectral reflectance properties range from 0.4 μm to 10.0 μm are numerically investigated via the Finite-Difference Time-Domain (FDTD) method. The effects of water film thickness, incidence angle, and geometric structure of micropit are examined. The results indicate that spherical approximation for the water film meniscus morphology has a visible deviation in reflectance especially within the 1.0 μm–3.5 μm waveband, up to 19.6% at 3.0 μm. The presence of water film exhibits a distinct decline in the spectral hemispherical reflectance at certain wavelengths, nearly up to 0.61. Under oblique incidence, the distribution of reflected energy peak shifts depending on the wavelength and microstructure, and meanwhile multiple peak regions occur. Besides, microstructure geometry has a pronounced effect on the spectral reflectance characteristics at a relatively small film thickness.