Discrete dipole approximation enhancement

Since enhanced electromagnetic fields in proximity to metal nanoparticles are the basis for the increased system absorption, various computational methods are available to predict the extent of the net system absorption and therefore potentially model the relative increase in singlet oxygen generation from photosensitizers. " In comparison to traditional Mie theory, more accurate computational methods, such as discrete dipole approximation (DDA/ or finite difference time domain (FDTD) methods, are often implemented to more accurately approximate field distributions for larger particles with quadruple plasmon resonances, plasmon frequencies of silver nanoparticles, or non-spherical nanoparticles in complex media or arrangements. ... 

Figure 5.2 E-field enhancement contours external to monomers with different shapes, (a] and (b] are the E-field enhancement contours external to a triangular prism polarized along the two different primary symmetry axes, (c] and (d] are the E-fields enhancement contours for a rod and spheroid polarized along their long axes. The arrows show where is the maximum of E-filed. Results are obtained numerically via the discrete dipole approximation (DDA] method. Reprinted with permission from Ref. [64]. Cop5rright [2004], American Institute of Physics.

Draine, B. T. (1988) The discrete-dipole approximation and its application to interstellar graphite grains, Astrophys. /., 333,848-872. Metiu, H. (1984) Surface enhanced spectroscopy. Prog. Surf. Sci, 17,... 

Large enhancements due to the effect of a high-permittivity substrate were also reported by D Agostino et al. [27] they studied fluorescence from CdSe/ZnS core/shell nanocrystals in proximity to silver nanospheres on an Ag-coated substrate. D Agostino demonstrated the role of this substrate in the observed enhancement by calculating the local field-enhancement factor using a Green s function refinement of the discrete dipole approximation this allowed retardation effects to be taken into account. 

---