Comparison of Methods for Reducing the Effects of Scattering in Spectrophotometry

Abstract

Light scattering provides a problem in optical spectroscopy as the relationship between attenuation and absorption in the presence of scattering is nonlinear. Three simple methods of reducing the effects of scattering and hence returning to an approximately linear relationship are considered in this paper, namely, extracting light that has maintained its original polarization state through subtraction of orthogonal polarization states, use of an added absorber, and spatial filtering. These can all be applied relatively easily to conventional spectrophotometers. However, there is an inevitable trade-off between the accuracy of the measurement and the signal-to-noise ratio as scattered light is rejected from the detector. It is demonstrated that polarization subtraction is the most efficient technique at selecting weakly scattered photons from a scattered light background as it enables the relationship between attenuation and absorption coefficient to become more linear while maintaining a higher number of detected photons. In practical use, the drawback of polarization subtraction over added absorber and spatial filtering methods is that a large dc background light level is maintained, which contributes to a higher shot noise. This means that when the scattering coefficient is high (micros > or = 7 mm(-1)) the added absorber method offers better performance for shot noise limited detection.

Molecular fingerprinting of nanoparticles in complex media with non-contact photoacoustics: beyond the light scattering limit

“…The problem of extracting light absorption from UV-VIS spectra for media exhibiting a significant scattering background was reported years ago 6 – 9 , and some pure optical methods have been developed to minimize its effects 6 , 8 , 9 . However, these techniques cannot be easily incorporated into conventional spectrometers or multi-spectral devices due to their complexity.…”

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

“…From these results, the failure to recover the absorber's pure spectrum from the raw reflectance spectra, support the fact that interactions in the mixture are responsible of non-linearities which are directly responsible of the nonlinearities in the relationship between the absorbance and the absorbing power of the sample. It is well known 20,32 that scattering and absorbance are not independent phenomenon. Scatter increases the mean free path of photons, which increases the chances of being absorbed.…”

“…Whereas separating absorption and scattering from a VIS-NIR signal is still an open research issue on highly turbid samples, the main demand from VIS-NIR spectroscopists is merely for spectra with reduced impact of scattering in order to better fit Beer-Lambert's Law conditions 19,20 .…”

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

“…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.…”