Miniaturized optical micro-probe for sizing in multiple scattering systems

Instruments based on photon counting in the visible part of the spectrum with subsequent signal autocorrelation of the light intensity fluctuation are widely used for the characterisation of clear media, but are performance limited if multiple scattering samples or particle suspensions with an inherent diffusion limitation are probed. These systems are classified as turbid media. We give advanced approaches as to how multiple scattering systems predominantly existing in industry can be examined, in order to resolve the sizes of suspended scattering centres. Latex particles and emulsions were used as models. Monte Carlo calculations of the light transport mechanisms in turbid media were performed and compared with measurements. A dynamic light scattering instrument was used to perform measurements on highly concentrated and turbid samples. For example, with particle standards of 83nm, a size of 85nm ± 5.8nm (n = 10) was obtained and particles with a size of 895nm were measured to be 895nm ± 9.1 nm (n = 10). The influence of multiple scattering on the autocorrelation function was both measured and calculated. We have shown that our calculations are in good agreement with the test results obtained and it was found that our miniaturised instrument is a valuable tool to measure particle sizes in turbid media.