Laser light scattering in turbid media Part I: Experimental and simulated results for the spatial intensity distribution

Abstract

We investigate the scattering and multiple scattering of a typical laser beam (lambda = 800 nm) in the intermediate scattering regime. The turbid media used in this work are homogeneous solutions of monodisperse polystyrene spheres in distilled water. The two-dimensional distribution of light intensity is recorded experimentally, and calculated via Monte Carlo simulation for both forward and side scattering. The contribution of each scattering order to the total detected light intensity is quantified for a range of different scattering phase functions, optical depths, and detection acceptance angles. The Lorentz-Mie scattering phase function for individual particles is varied by using different sphere diameters (D = 1 and 5 mum). The optical depth of the turbid medium is varied (OD = 2, 5, and 10) by employing different concentrations of polystyrene spheres. Detection angles of theta(a) = 1.5 degrees and 8.5 degrees are considered. A novel approach which realistically models the experimental laser source is employed in this paper, and very good agreement between the experimental and simulated results is demonstrated. The data presented here can be of use to validate any other modern Monte Carlo models which generate spatially resolved light intensity distributions. Finally, an effective correction procedure to the Beer-Lambert law is proposed based on the Monte Carlo calculation of the ballistic photon contribution to the total detected light intensity.

Improved Monte Carlo model for multiple scattering calculations

“…With D=5 µm particles at OD=10, the FWHM predicted by the old and the new models differs by ∼5% (3.43 mm versus 3.27 mm). The experimentally measured FWHM was 3.19 mm in this case [6] . Therefore, both the old and the new models over-predicted the FWHM, by ∼7.5% and ∼2.5% relative to the experimental measurements, respectively.…”

“…On the other hand, the limitations of the MC method are also well recognized, and the development of new MC methods continues to be an active area of research. For example, considerable progress has been made in the experimental validation of MC methods [6,7] and in the improvement of their efficiency [9,10] . Meanwhile, new MC methods have been developed to track the polarization during multiple scattering [11,12] and to capture the propagation of an ultra-short laser pulse in optically dense media [13] .…”

“…(2)-(6) have been discussed previously [15,16] , but they are also often neglected [1,6,7] . Therefore, one goal of this study is to quantitatively examine such effects.…”

“…We first briefly summarized the experiments performed in Refs. [6,18] to facilitate the discussion in this study.…”

Scaling Law for Photon Transmission through Optically Turbid Slabs Based on Random Walk Theory

“…However, multiple-scattering problems usually are complicated and have to be solved numerically, which is computationally costly and often does not provide intuitive understanding of the problem. As an example, Monte Carlo simulation [3][4][5][6], which is an extensively used numerical technique, can be prohibitively expensive when probing large optical depth. Considerable efforts have been investigated to overcome this limitation, and one notable technique demonstrated recently [7] involves the use of GPU (Graphical Processing Units) to parallelize and accelerate Monte Carlo simulations.…”