Polarized light diffuse reflectance FT-NIR MEMS spectrometer enabling the detection of powder samples through a thin...

Area of Science:

• Spectroscopy
• Optical Engineering
• Materials Science

Background:

• Fourier transform infrared (FTIR) spectroscopy is crucial for analyzing materials, but struggles with highly scattering samples due to multiple scattering effects.
• Existing methods for in-vivo, agricultural, and environmental monitoring face challenges in accurately quantifying absorbance in complex scattering media.
• Polarized light techniques offer potential for overcoming scattering limitations in spectroscopic measurements.

Purpose of the Study:

• To develop and validate a microelectromechanical system (MEMS)-based FTIR spectrometer utilizing polarized light for accurate absorbance measurements.
• To enable the differentiation between single backscattering from surface layers and multiple scattering from deeper layers in heterogeneous samples.
• To demonstrate the effectiveness of the developed technique in reducing errors associated with scattering in diffuse reflectance measurements.

Main Methods:

• A MEMS-based FTIR spectrometer with a bistate polarizer was employed in a diffuse reflectance setup.
• The spectrometer operates in the extended near-infrared (NIR) range (1300-2300 nm) with a spectral resolution of 64 cm⁻¹.
• The technique involves de-embedding the spectrometer's polarization response through normalization, applied to milk powder, sugar, and flour samples with varying particle sizes (10-400 µm).

Main Results:

• The developed spectrometer successfully distinguished between single and multiple scattering events.
• Absorbance spectra extracted using the proposed technique showed good agreement with direct diffuse reflectance measurements.
• The calculated error for flour samples at 1935 nm was significantly reduced from 43.2% to 2.9%, with reduced wavelength error dependence.

Conclusions:

• The polarized light MEMS-FTIR spectrometer offers a robust solution for accurate absorbance measurements in highly scattering materials.
• This technique effectively mitigates errors caused by multiple scattering, enhancing the reliability of spectroscopic analysis.
• The demonstrated capability has significant implications for applications in food science, pharmaceuticals, and environmental monitoring where sample scattering is a challenge.