Modelling Optical Properties of Algae Using the Finite-Difference Time Domain Method

Abstract Photosynthetic microorganisms are important to the Earth’s ecosystem, since about half of the atmospheric oxygen is produced by photosynthesis. Microalgae and photosynthetic bacteria are also utilized in a wide range of industries in photobioreactors. In order to have better control over photobioreactors under various operating conditions, it is necessary to accurately characterize the propagation of light in the reactor. Theoretical methods are able to calculate the optical properties of microorganisms through the solution of Maxwell’s equations of electromagnetic wave theory. To solve Maxwell’s equations, various methods can be used including Lorenz-Mie, T-Matrix, Finite-Difference Time-Domain (FDTD), and Volume Integral methods. Most theoretical methods predict the optical properties of microorganisms by Lorenz-Mie theory. Lorenz–Mie theory is applicable for homogeneous and spherical particles, homogeneous concentric spheres, or coated spheres. This work seeks to determine the suitability of the commonly used homogenous-sphere, coated-sphere, and heterogenous-sphere approximation by simulating the optical behavior of photosynthetic microorganism (Chlamydomonas reinhardtii) using FDTD and an accurate geometric model. Here, each of the key cell organelles will be included in the model with the appropriate optical properties specified. These results allow for a more accurate optical model to be developed while studying the effects of different growth regimes.