Fitting oscillator models to variable-angle spectroscopic ellipsometry (VASE) data can lead to non-unique, unphysical results. We demonstrate using temperature-dependent trends to prevent overfitting and ensure model physicality. As a case study, we performed mid-infrared VASE measurements on fused silica (SiO2) of various grades, from room temperature to 600 {\deg}C. We fitted oscillator models independently at each temperature, and confirmed the model's physical validity by observing the expected monotonic trends in vibrational oscillator parameters. Using this technique, we generated a highly accurate dataset for the temperature-dependent complex refractive index of fused silica for modeling mid-infrared optical components such as thermal emitters.
@article{arxiv.2409.05323,
title = {Preventing overfitting in infrared ellipsometry using temperature dependence: fused silica as a case study},
author = {Shenwei Yin and Jin-Woo Cho and Demeng Feng and Hongyan Mei and Tanuj Kumar and Chenghao Wan and Yeonghoon Jin and Minjeong Kim and Mikhail A. Kats},
journal= {arXiv preprint arXiv:2409.05323},
year = {2025}
}
Comments
Main text + supplementary (updated June 16, 2025). The data can be found at this Zenodo record: https://zenodo.org/records/15178466