The three-dimensional (3D) finite-difference time domain (FDTD) technique has been extended to simulate light scattering and absorption by particles embedded in an absorbing dielectric medium. A uniaxial perfectly matched layer (UPML) absorbing boundary condition (ABC) in Sacks et al. (1995) is used to truncate the computational domain. We have formulated a numerical scheme to simulate the propagation of a plane-wave pulse in a homogeneous dielectric medium. We have also used an equalization factor in the FDTD scheme to reduce errors related to the incident plane-wave source. In computing the single scattering properties of a particle in an absorbing dielectric medium, we derive scattering phase functions, extinction and absorption rates by using a volume integration of field inside the particle.

A Mie solution for light scattering and absorption by spherical particles in an absorbing medium developed by Fu and Sun (2001) is used to examine the accuracy of the FDTD code. It is found that the errors in the extinction and absorption efficiencies from the UPML FDTD are smaller than 2%. The errors in the scattering phase functions are typically smaller than 5%. The errors in the asymmetry factors are smaller than 0.1%. For light scattering by particles in free space, the UPML FDTD scheme shows a similar accuracy as our previous model (Sun et al. 1999), though the formulations of PML and UPML have different Gauss' Laws.

With use of UPML ABC, the memory requirement for boundary layer has been further reduced and the simulation can be done on a personal computer for a size parameter as large as 20. This generalized FDTD scheme might have potential applications to remote sensing of water color, modeling target response to ground penetration radar (GPR) wave, and biomedical study. The dynamic memory allocation feature of C++ makes this model user-friendly and easily integrated into optical software for the study of electromagnetic wave propagation and scattering and for fiber optics applications.