Effects of Polarizer-Analyzer Configurations for FTIR Spectroscopy: Implications for Multiple Polarization Algorithms

Area of Science:

• Spectroscopy
• Materials Science
• Physical Chemistry

Background:

• Polarized Fourier transform infrared (p-FTIR) spectroscopy is crucial for analyzing molecular orientation in organic materials.
• Conventional p-FTIR uses a single polarizer, but a second polarizer (analyzer) can introduce unexpected spectral variations.
• These polarization-dependent variances, stemming from sample-induced changes in light polarization, have not been fully investigated in p-FTIR.

Purpose of the Study:

• To investigate the impact of a second polarizer on p-FTIR spectra of anisotropic organic samples.
• To explore theoretical and experimental effects of polarizer-analyzer configurations in p-FTIR.
• To identify new analytical possibilities for p-FTIR, particularly for sample anisotropy detection.

Main Methods:

• Utilized both theoretical modeling and experimental measurements.
• Analyzed spectral variances induced by birefringence in thin anisotropic organic samples.
• Investigated the effects of crossed and parallel polarizer configurations.

Main Results:

• The most significant spectral variance due to birefringence in thin samples appears on the shoulders of dichroic peaks.
• A crossed polarizer configuration enables anisotropy detection in samples typically too thick for standard p-FTIR.
• The standard squared-cosine relationship for absorptance is inaccurate with a second parallel polarizer.

Conclusions:

• The inclusion of a second polarizer in p-FTIR can significantly influence spectral data and analytical outcomes.
• Exploiting spectral features on dichroic peak shoulders with a crossed polarizer offers a novel method for analyzing thicker anisotropic materials.
• A modified function is proposed to accurately describe absorptance in multiple polarizer configurations for p-FTIR analysis.