Direct method of extracting broadband complex refractive index from spectrophotometric measurements: an application to polydimethylsiloxane for passive radiative cooling

We describe an algorithm to extract the complex refractive index of a material from broadband reflectance and transmittance measurements taken by spectrophotometers. The algorithm combines Kramers-Kronig analysis with an inversion of Fresnel's equations to provide a direct method of solving for the refractive index which is accurate, even for weakly absorbing materials, and easily applicable to radiative heat transfer calculations. The algorithm is validated by extracting the complex refractive index of polydimethylsiloxane between 0:25 mu m and 100 mu m and comparing against existing literature. We also discuss the importance of broadband optical properties to passive radiative cooling and details of the uncertainty analysis of the algorithm. Published by SPIE

Automated summary

The algorithm discussed in the study combines Kramers-Kronig analysis with Fresnel's equations inversion to accurately extract the complex refractive index of materials from broadband reflectance and transmittance measurements, even for weakly absorbing materials. The validation of the algorithm on polydimethylsiloxane and comparison against literature showcases its effectiveness. Furthermore, the study highlights the importance of broadband optical properties for passive radiative cooling and provides details on the uncertainty analysis of the algorithm.