WRH professors Junko Morikawa and Saulius Juodkazis (School of Materials and Chemical Technology) published a paper in Laser & Photonics Reviews.

“RGB-Color Image Analysis for Determination of Birefringence of Micro-Films and Columnar Coatings”

https://doi.org/10.1002/lpor.202200535

Abstract:
The birefringence analysis of thin $\approx 1\hspace*{3.33333pt}\umu $m SiO₂ films deposited via evaporation at a glancing angle of $\hspace*{3.33333pt}{70}^{\circ}$ to the normal on resist pillar arrays on Si and nanopatterned SiO₂ substrates is carried out by spectral and color (red–green–blue [RGB]) imaging modes. Retardance and birefringence of the films deposited over flat and structured regions can be distinguished with only ≈1% difference between neighboring regions for the visible spectral range using RGB numerical analysis of images. The Michel-Lévy color map is used for color rendering of birefringence to make quantitative measurements by numerical RGB color filtering. It is shown that by using $\lambda /2$ at 530 nm waveplate inserted at $\pi /4$ angle to the cross polarizer-analyzer setup, the range of changes in chromaticity xy-coordinates expands approximately twice upon angular rotation of a birefringent sample. This facilitates a better signal-to-noise determination of birefringence. The proposed method with $\lambda /2$-plate color shifting can be directly used to determine birefringence from step-like spectral features in reflection and transmission polariscopy. Direct measurement of birefringence (${\Delta}n=0.023$) and retardance of SiO₂ chevron film is carried out using Berek compensator as a benchmark.