Equation (8) was incorrect.
© 2008 Optical Society of America
The numerical analysis in Ref.  was performed with the above correct equation.
References and links
1. T. Yamaguchi and T. Hinata, “Optical near-field analysis of spherical metals: Application of the FDTD method combined with the ADE method”, Opt. Express 15, 11481–11491 (2007). http://www.opticsexpress.org/abstract.cfm?id=141035 [CrossRef] [PubMed]