Three-Dimensional Computation of Focused Beam Propagation through Multiple Biological Cells

A massively parallel finite difference time domain method was used to compute scattering of a focused optical beam by multiple heterogeneous biological cells. A perfectly matched layer boundary condition and the scattered-field-only method were utilized in the simulation to increase accuracy and computational efficiency. A fifth-order approximation to the focused Gaussian beam was used for the incident field. A parametric study was performed to determine scattering effects of varying cellular fine structure, such as nuclear refractive index, organelle volume density, cellular shape and the cell membrane on the point spread function (PSF) of the beam. It was found that two-photon PSF is largely unaffected by increasing numbers of scatterers within cells, while two-photon excitation signal strength is dependent on both beam focal depth and the density of scatterers in tissue.