Sophisticated Attenuated Total Reflection Correction Within Seconds for Unpolarized Incident Light at 45°

Area of Science:

• Spectroscopy
• Physical Chemistry
• Materials Science

Background:

• Standard mid-infrared (MIR) attenuated total reflection (ATR) accessories at 45° incidence lack polarizers, limiting spectral correction accuracy.
• Strong MIR peaks are susceptible to refractive index changes from anomalous dispersion, complicating ATR correction.
• Existing ATR correction methods can be computationally intensive and time-consuming.

Purpose of the Study:

• To develop a rapid and accurate method for ATR correction of MIR spectra.
• To determine the complex refractive index function from ATR measurements.
• To enhance the sophistication of ATR spectral analysis.

Main Methods:

• Utilizing a 45° ATR spectrum recorded without a polarizer and the polarization angle from the same Fourier transform infrared spectroscopy (FTIR) system.
• Applying an improved non-iterative Kramers-Kronig analysis to derive the complex refractive index.
• Simulating potential error sources like incidence angle spread and polarization angle dispersion.

Main Results:

• The combined spectral and polarization data provide sufficient information to determine the ATR s-polarized spectrum.
• The non-iterative Kramers-Kronig analysis yields the complex refractive index function rapidly (within seconds).
• The method was successfully applied to water and octadecane using various ATR crystals and accessories.

Conclusions:

• The developed formalism offers a significantly faster (two orders of magnitude) alternative to iterative methods for ATR correction.
• This advanced ATR correction method enhances the accuracy of MIR spectral analysis, especially for samples with strong peaks.
• The study validates the method's effectiveness and investigates potential error sources for broader applicability.