The effect of absorption in diffusing wave spectroscopy (DWS) was studied using an absorption-dependent diffusive equation for describing the light propagation within a turbid liquid where dielectric microspheres have been embedded. Here, we propose an expression for the time-averaged light intensity autocorrelation function that correctly describes the time fluctuations for the scattered light, in the regime where the diffusion approximation accurately describes the light propagation. This correction was suspected previously, but it was not formally derived from a light diffusive equation. As in the case of no absorption, we obtained that time fluctuations of the scattered light can be related to the mean square displacement of the embedded particles. However, if a correction for absorption is not taken into account, the colloidal dynamics can be misinterpreted. Experimental results show that this new formulation correctly describes the time fluctuations of scattered light. This new procedure extends the applicability of DWS, and it opens the possibility of doing microrheology with this optical method in systems where absorption cannot be avoided.
In this paper, we present and validate a new method for optical properties recovery of turbid media with slab geometry. This method is an iterative method that compares diffuse reflectance and transmittance, measured using integrating spheres, with those obtained using the known algorithm MCML. The search procedure is based in the evolution of a population due to selection of the best individual, i.e., using a genetic algorithm. This new method includes several corrections such as non-linear effects in integrating spheres measurements and loss of light due to the finite size of the sample. As a potential application and proof-of-principle experiment of this new method, we use this new algorithm in the recovery of optical properties of blood samples at different degrees of coagulation.
When a nanosecond laser pulse is transmitted through a highly scattering material, its irradiance decreases as it propagates; this is because of the spatial and temporal pulse profile stretching owing to multiple scattering events. Although the effect of temporal distortion is much less significant than that of the spatial distortion for applications where the laser beam is focused on a subsurface target (writing of waveguides, for example), it becomes significant for applications where the laser pulse must attain certain temporal width after the beam propagated is collimated through a turbid medium (photoacoustic tomography, for example). The objective of this work is to determine the transfer function associated to an integrating sphere measurement of the temporal intensity profile involving turbid media samples. The transfer function is found to be related to the geometrical characteristics of the integrating sphere and the optical properties of the turbid media. This procedure opens a new possibility for optical property characterization and enables the use of an integrating sphere for time-dependent intensity measurements.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.