Istituto Nazionale di Ricerca Metrologica (INRiM), Torino, Italy.
European Laboratory for Nonlinear Spectroscopy (LENS), Sesto Fiorentino, Italy.
J Biomed Opt. 2022 Jun;27(8). doi: 10.1117/1.JBO.27.8.083020.
Most radiative transport problems in turbid media are typically associated with mm or cm scales, leading to typical time scales in the range of hundreds of ps or more. In certain cases, however, much thinner layers can also be relevant, which can dramatically alter the overall transport properties of a scattering medium. Studying scattering in these thin layers requires ultrafast detection techniques and adaptations to the common Monte Carlo (MC) approach.
We aim to discuss a few relevant aspects for the simulation of light transport in thin scattering membranes, and compare the obtained numerical results with experimental measurements based on an all-optical gating technique.
A thin membrane with controlled scattering properties based on polymer-dispersed TiO2 nanoparticles is fabricated for experimental validation. Transmittance measurements are compared against a custom open-source MC implementation including specific pulse profiles for tightly focused femtosecond laser pulses.
Experimental transmittance data of ultrafast pulses through a thin scattering sample are compared with MC simulations in the spatiotemporal domain to retrieve its scattering properties. The results show good agreement also at short distances and time scales.
When simulating light transport in scattering membranes with thicknesses in the orders of tens of micrometer, care has to be taken when describing the temporal, spatial, and divergence profiles of the source term, as well as the possible truncation of step length distributions, which could be introduced by simple strategies for the generation of random exponentially distributed variables.
混浊介质中的大多数辐射传输问题通常与毫米或厘米尺度相关，导致典型的时间尺度在数百皮秒或更长时间范围内。然而，在某些情况下，也可能涉及更薄的层，这会显著改变散射介质的整体传输特性。研究这些薄层中的散射需要超快检测技术和对常见的蒙特卡罗（MC）方法的适应。
我们旨在讨论在薄散射膜中模拟光传输的几个相关方面，并将获得的数值结果与基于全光学门控技术的实验测量进行比较。
基于聚合物分散的 TiO2 纳米粒子，制备了具有受控散射特性的薄膜，用于实验验证。透射率测量与定制的开源 MC 实现进行了比较，该实现包括针对紧密聚焦飞秒激光脉冲的特定脉冲分布。
通过薄散射样品的超快脉冲的实验透射率数据与时空域中的 MC 模拟进行了比较，以恢复其散射特性。结果在短距离和时间尺度上也显示出良好的一致性。
当模拟厚度为数十微米量级的散射膜中的光传输时，必须注意源项的时间、空间和发散分布的描述，以及可能由于简单的生成随机指数分布变量的策略而引入的步长分布截断。
