Proceedings Article | 1 August 2021
KEYWORDS: Speckle pattern, Statistical analysis, Monte Carlo methods, Geometrical optics, Computer simulations, Sensors, Optical simulations, Analytical research, Scattering, MATLAB
A coherent beam of incident light that impinges on a turbid medium or a rough surface, generates a characteristic interference pattern called "speckle". In this research work, was modeled the speckle pattern due to volumetric scattering within a turbid medium by using Monte Carlo simulations in OpticStudio® when the optical parameters (OP) of the medium were kept constant. A variable number of analysis rays from the light source was considered in order to evaluate the adequacy of the statistical distribution of intensities and its agreement to fully developed speckle (FDS) as predicted by the theory. In the non-sequential mode of OpticStudio®, it was implemented an optical setting of diffuse reflection geometry composed of: a coherent light source (Source Ellipse), a scattering volume (Rectangular Volume), and a detector (Rectangle Detector) with dimensions typical of a realistic sensor. The source was configured with a coherence length of 50x103 mm, a linear polarization along the x-axis (Jx =1), and a diameter beam of 1 mm. The OP of the scattering volume were defined using the Henyey-Greenstein scattering model with the following parameters: mean path MP = 0.1 mm, transmission T = 0.9, and anisotropy factor g= 0.95. Detector settings were established as: dimension= 4.8x3.8 mm2, resolution= 1328x1048 pixels, and Polarization Flag= 1. The study was performed for 2, 5, 10, 15, 20, 25, 30, 50, 75, 100 and 500 million analysis rays launched from the light source. The goodness of fit between simulated normalized histograms of intensity and the negative exponential probability density function of speckle patterns predicted by the theory was determined by using the software Minitab®. It was demonstrated that a good agreement between these previous mentioned quantities is achieved for the higher number of analysis rays. This study provides a guideline about a threshold number of analysis rays that should be used in OpticStudio® when simulations of coherent scattering in turbid media are performed. This study could also impact in different fields of speckle metrology by predicting results using OpticStudio® during the modeling specific optical configurations.
