If coherent light is incident on a suspension containing nanoparticles, the result of the far field interference is a
"speckled" image. As a consequence of the complex Brownian motion the speckle image is not static but presents time
fluctuations. A computer code to simulate the dynamics of the coherent light scattering on nanofluids was written, tested
and used.
Light scattering on particles having the diameter comparable with the wavelength is accurately described by the Mie
theory and the light scattering anisotropy can conveniently be described by the one parameter Henyey Greenstein phase
function. An aqueous suspension containing magnetite nanoparticles was the target of a coherent light scattering
experiment. By fitting the scattering phase function on the experimental data the scattering anisotropy parameter can be
assessed. As the scattering parameter strongly depends of the scatterer size, the average particle diameter was thus
estimated and particle aggregates presence was probed. This technique was used to investigate the nanoparticle
aggregation dynamics and the results are presented in this work.
The single act light scattering anisotropy is conveniently described using the Henyey-Greenstein phase function when
the scattering centers dimension is comparable or bigger than the wave length. When the concentration increases, a
different phase function can be used. For a certain scattering angle the calculated light scattering intensity variation with
the optical depth of the target is analyzed and compared with the experimental data recorded on mud in aqueous
suspension. The results suggest a very fast method for measuring very small concentration in suspensions, in the range of
μg/l.
When coherent light passes through a transparent fluid having scattering centers (SC) in suspension the result of the far
field interference is a "speckled" image. In suspension the SCs have a complex sediment and Brownian motion.
Consequently the biospeckle image is not static but presents time fluctuations. A computer code to simulate the
dynamics of the coherent light scattering on biological suspensions was written and used to investigate typical
biological suspensions like erythrocytes (RBC) and milk in deionized water. The calculated far field intensity variation
was analyzed with the autocorrelation function. Practical application are suggested based on the simulation results.
When coherent light is incident upon an optically thick biological fluid having scattering centers (SC) in suspension,
like whole blood, the backscattered light can be recorded, resulting an image speckle. A program was written to extract
the time series from each pixel of the CDD conversion matrix. The autocorrelation time of the series was calculated and
the autocorrelation time was determined on blood samples from different human subjects. The autocorrelation time was
analyzed and compared with the erythrocyte sedimentation rate (ESR) measured during a standard laboratory test using
the modified Westergren method. A different procedure to record the time series, using a detector and a data acquisition
system was used as well and the autocorrelation time was calculated for the time series recorded using this procedure.
The results of the work performed so far indicate that the two properties appear to be slightly correlated. A fast
procedure for assessing the ESR is suggested.
In biological suspensions light scattering is done mainly by the contribution of the suspended cells. A main challenge in
describing light diffusion is to produce an analytical expression that accurately expresses the multiple light scattering
anisotropy. The Henyey-Greenstein phase function embedded in the RWMCS code was used to describe single
scattering on Red Blood Cells in suspension. The results of the simulation, containing multiple light scattering, are used
to verify the predictions of two new effective phase function recently published. The results show a good agreement in
the small RBC concentration range.
A modified version of the Laser Speckle Contrast Analysis technique was developed. It is different of the typical
LASCA technique as the laser beam is not reflected by the object but transmitted through a cuvette containing a diluted
suspension. A digital image with speckles is taken and the time contrast not the space contrast is calculated, which is the
second main difference from the typical LASCA technique. The contrast is converted into colors and a contrast image,
hence a velocity map is obtained. The results of analyzing different biological suspensions with this technique are
presented and the possibility of using it for micrometric particle motion and as a fast diagnosis method is discussed.
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