| Laser speckle phenomenon is an impartant phenomenon of coherent optical transmission, which has a wide range of applications in the industrial, life sciences, such as displacement measurement, laser speckle imaging of blood flow. Scattering in the biological tissue and aqueous solution of suspended particles are mostly volume scattering, which always contain multiple scattering. Such speckle phenomenon is very complex, which is difficult to be solved by the waveequation and generally is simulated using numerical methods. But the traditional Monte Carlo simulation tend to ignore the movement of the properties of the medium, so it can’t be used to simulate the speckle phenomenon during Brownian motion, directional flow of the scattering media, which is precisely very important to study the properties of dynamic speckle of volume scattering and to realize a quantitative measure of velocity. In response to these problems, this paper firstly simulate the dynamic speckle in continuous time sequence, and present a new method of dynamic speckle simulation, and analyzed the autocorrelation function of the translational speckle and boiling speckle. Then we present the relationship between velocity and the autocorrelation function of electric field under the action of both translational speckle and boiling speckle (traditional research methods thought that velocity is inversely proportional to the decorrelation time of electric field). Then a model of dynamic turbid scattering media is presented, and the speckle field of scattering media contains both directional flow and Brownian motion is simulated and analyzed with a developed Monte Carlo simulation method, supplying a tool to analyze the speckle properties of volume scattering and the factors of velocity measurement. The specific content including:(1) Using the gamma distribution to analyse the speckle phenomenon, proposed a smaller value, present a new method to simulate the dynamic speckle in continuous time sequence, and simulate the translational speckle and boiling speckle with Lorentzian profile. Then we present a relationship between velocity and the autocorrelation function of electric field, and analyze the relationship between the velocity and the contrast.(2) Extend the electric field Monte Carlo simulation from infinitely narrow beam to finite-size beam. In order to cover the increase of the amount of computation, we present a parallel implementation based on CUDA the compute unified device architecture (CUDA) running on a graphics processing unit (GPU), called CUDAEMC. With a GTX480Fermi GPU, we achieve a370x speedup when calculating backscattering speckle patterns with single precision compared to an i3-2120CPU.(3) Present a electric field Monte Carlo simulation based on particle system, called DMEMC, which can simulate the Brownian motion and directional flow of a media model of the suspended particulates solution. Based on this, the speckle field of volume scattering of moving media is simulated and analysed. And then the Monte Carlo simulation of volume scattering of moving scatterers illuminated by a coherent light could be done. |
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