Improvement of the Chemical Content Prediction of a Model Powder System by Reducing Multiple Scattering Using Polarized Light Spectroscopy

Abstract

Near-infrared spectroscopy (NIRS) is a powerful non-destructive analytical method used to analyze major compounds in bulk materials and products and requiring no sample preparation. It is widely used in routine analysis and also in line in industries, in vivo with biomedical applications, or in field for agricultural and environmental applications. However, highly scattering samples subvert Beer-Lambert law's linear relationship between spectral absorbance and the concentration. Instead of spectral pre-processing, which is commonly used by NIR spectroscopists to mitigate the scattering effect, we put forward an optical method, i.e., coupling polarized light with NIR spectrometry, to free spectra from scattering effect. This should allow us to retrieve linear and steady conditions for spectral analysis. When tested in visible-NIR (Vis-NIR) range (400-800 nm) on model media, mixtures of scattering and absorbing particles, the setup provided significant improvements in absorber concentration estimation precision as well as in the quality and robustness of the calibration model.

A New Optical Sensor Based on Laser Speckle and Chemometrics for Precision Agriculture: Application to Sunflower Plant-Breeding

“…First of all, the average intensities of the images − pp and − ps were computed: , . is the sum of the polarization maintaining light and half of the depolarized light, whereas corresponds to half of the depolarized light [ 27 ]. The average surface and volume intensities, respectively and were then defined as: …”

Combining light polarization and speckle measurements with multivariate analysis to predict bulk optical properties of turbid media

“…First of all, the average intensity of the images -pp and -ps were computed: <I pp >, <I ps >. <I pp > is the sum of the polarization maintaining light and half of the depolarized light, whereas <I ps > corresponds to half of the depolarized light [41]. The average surface and volume intensity, respectively I surf and I vol were then defined as:…”

A new optical method coupling light polarization and Vis–NIR spectroscopy to improve the measurement of soil carbon content

“…Secondly, as they rely on the estimation of absorption and scattering coecients achieved by model inversion, parameters describing the studied medium (sample thickness, refractive index, particle size and shape...) must be known or approximated, which may be a troublesome task as they are often unknown in complex media (Steponavicius & Thennadil, 2011;Swartling et al, 2003). Bendoula et al (2015) proposed to combine light polarization and VIS-NIR reectance spectra acquisitions. The Polarized Light Spectroscopy (Po-LiS) method is an original technique to reduce directly the eects of multiscattering on the measured signal by using the wave theory of light (Lu et al, 2006;Backman et al, 1999).…”

“…When linearly polarized light interacts with a scattering material, the backscattered light progressively looses its initial polarization and oscillates randomly in all the planes. Using the principle of polarization subtraction, Bendoula et al (2015) measured a reectance spectra being less impacted by multiscattering. In Gobrecht et al (2015), the signals measured with the PoLiS method were processed in the frame of Dahm's Representative Layer Theory (Dahm & Dahm, 2007) (Table 1).…”

“…From these measurements, the backscattered reectance, R BS (λ), and the weakly scattered reectance, R SS (λ), were computed for each sample according to Bendoula et al (2015):…”