Wielaard, D.J., M.I. Mishchenko, A. Macke, and B.E. Carlson, 1997: Improved T-matrix computations for large, nonabsorbing and weakly absorbing nonspherical particles and comparison with geometric optics approximation. Appl. Opt., 36, 4305-4313.
We show that using a matrix inversion scheme based on a special LU factorization rather than on the standard Gaussian elimination significantly improves the numerical stability of T-matrix computations for nonabsorbing and weakly absorbing nonspherical particles. As a result, the maximum convergent size parameter for particles with small or zero absorption can increase by a factor of several and can exceed 100. We describe an improved scheme for evaluating Clebsch-Gordon coefficients with large quantum numbers which allowed us to extend the analytical orientational averaging method developed by Mishchenko [J. Opt. Soc. Am. A 8, 871 (1991)] to larger size parameters. Comparisons of T-matrix and geometric optics computations for large, randomly oriented spheroids and finite circular cylinders show that the range of applicability of the ray tracing approximation depends on the imaginary part of the refractive index and is different for different elements of the scattering matrix.