NOTICE: Due to a lapse in annual appropriations, most of this website is not being updated. Learn more.
Form submissions will still be accepted but will not receive responses at this time. Sections of this site for programs using non-appropriated funds (such as NVLAP) or those that are excepted from the shutdown (such as CHIPS and NVD) will continue to be updated.
An official website of the United States government
Here’s how you know
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.
Direct method of extracting complex refractive index from routine Fourier transform infrared reflectance/transmittance measurements
Published
Author(s)
Braden E. Czapla, Leonard M. Hanssen
Abstract
We describe an algorithm to extract the complex refractive index of a material from reflectance and transmittance measurements commonly 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. We discuss the details of the uncertainty analysis of the algorithm. The algorithm is validated by extracting the complex refractive index of polydimethylsiloxane between 2 micrometers and 18 micrometers and comparing against existing literature.
Czapla, B.
and Hanssen, L.
(2020),
Direct method of extracting complex refractive index from routine Fourier transform infrared reflectance/transmittance measurements, SPIE Optics Photonics 2020 Digital Forum, San Diego, CA, [online], https://doi.org/10.1117/12.2568502
(Accessed October 10, 2025)