SHEDDING SOME LIGHT INTO THE ELECTROMAGNETIC FIELD INSIDE HOT SPOTS

EDUARDO M. PERASSI; LUIS R. CANALI; EDIARDO A. CORONADO

Buenos Aires, Argentina

Conferencia; 10º International Conference on Near-field Optics,and Related Techniques; 2008

Laboratorio de Electrónica cuántica, Dpto de Fisica. UBA

 Understanding  the  factors which controls the way light interacts with matter in the nano scale is a fundamnetal issue in optoelectronics and nanophotonics, as many applications such as surface enhanced spectroscopies for  bio-chemical sensing, optical signal processiing relies on the surface bound optical excitations in metallic nanoparticles. An accurate evaluation of   of the electromagnetic field enhancement is of upmost importance to evaluate the relative contributions of  chemical and electromagnetic mechanism proposed for  SERS as well as to shed light into the problem of  feasibility  of  single molecule SERS  based on purely electromagnetic fields arguments. Although for some simple shapes such as spheres and spheroids analytical solutions to Maxweell equations make it possible to evaluate accurately the electromagnetic field enhancement,  for arbitrary shaped NPs one has to deal with numerical methods, which  relies on discretization of the NP on finite grids.  In this sense, two main problems arises: the converegence with respect to the grid size and the accuracy of the electromagnetic field near the NP surface. In this work ,  using the Discrete Dipole Approximation, we give an heuristic approach that allow us to shed some light into both problems, by  a novel approach based on an empirical variation law for the electromagnetic field enclosed by a finite volume. This approach is applied for an accurate evaluation of the hot spots generated around  some representative NP shapes such as  silver spheroids, cylinders and prisms.