Estimation and sensitivity of dielectric response functions for NIR-SWIR absorbing dyes using Kramers-Kronig analysis

Abstract

This study describes a Kramers-Kronig analysis of diffuse reflectance from NIR/SWIR-absorbing dyes on cotton fabric substrates for estimating dielectric response functions. The calculated response functions do not directly capture the dielectric functions of the dyes, which are material properties, but rather provide estimates of the dielectric response characteristics – including the dye and substrate interactions. Since the Kramers-Kronig analysis is applied to diffuse reflectance and not to specular reflectance from uniform bulk material surfaces, it cannot provide an exact determination of the material permittivity functions. However, the calculated response functions can support the construction of approximate effective medium models capable of estimating reflectance from dyed fabrics. This study investigates the construction of such models using the calculated dielectric response functions. Additionally, a sensitivity analysis explores the impact of the Kramers-Kronig integration range incompleteness by testing lower/upper wavelength smoothing and extrapolation techniques.