Nelly: A User-Friendly and Open-Source Implementation of Tree-Based Complex Refractive Index Analysis for Terahertz...

Area of Science:

• Physics
• Materials Science
• Spectroscopy

Background:

• Terahertz (THz) spectroscopy enables precise measurement of material properties, including refractive index and conductivity.
• Extracting complex refractive indices from THz time-domain spectroscopy data is challenging for multilayer samples due to numerous transmission-reflection paths.
• Existing approximation methods for THz data analysis are limited in applicability and can yield inaccurate results.

Purpose of the Study:

• To develop a robust and widely applicable method for accurately extracting complex refractive indices from THz time-domain spectroscopy data of multilayer samples.
• To provide an open-source software package implementing this novel analysis method.

Main Methods:

• Modeling all possible transmission-reflection paths of THz pulses through multilayer samples as a branching tree structure.
• Generating analytical expressions that relate the unknown refractive index to the observed time-domain data.
• Implementing the method in an open-source MATLAB library and a standalone graphical user interface (GUI).

Main Results:

• The developed tree-based path modeling method accurately extracts complex refractive indices from THz spectroscopy data.
• Comparison with commonly used approximations shows superior accuracy and wider applicability of the new method.
• The open-source package 'nelly' is validated for diverse sample types.

Conclusions:

• The novel path-modeling approach offers a significant improvement over traditional approximations for THz spectroscopy data analysis.
• The freely available 'nelly' package democratizes access to advanced THz material characterization.
• This method enhances the reliability and scope of applications for THz time-domain spectroscopy.