CALCULATION METHODS AT THE PLASMONIC. 2. DISCRETE-DIPOLE APPROXIMATION METHOD

Abstract

In this section we consider a method by which one can simulate a much larger class of plasmonic structures. The method of discrete-dipole approximation, or simply a method of discrete dipoles, as is clear from the title, represents any structure in the form of a collection of small particles that behave like dipoles. It is a direct consequence of the quasi-static approximation, that is, if the structure is larger than the wavelength of light, you can always break it into elements, each of which will be smaller. These elements will behave like dipoles, and to determine the properties of the structure, it is necessary to calculate the interaction of each dipole with the inverse field and with the field of all the dipoles of the structure. This allows to simulate the flow of any complexity, to calculate the interaction of the husband with the elements of the structure and with the external field, which is not available for other models.

This method has essential features that often interfere with the practice of modeling any structures. First, this is the complexity and ambiguity of breaking the volume of the structure into dipole elements. Secondly, it requires a large number of computations. Therefore, for the effective simulation, some optimizations, such as, for example, the parallelization of computations must be implemented. The review shows solutions to these problems and examples of numerous experiments.

Also, here are presented options for using the method tested by the authors. By means of the discrete-dipole approximation method, optical responses of particles of various shapes are modelled. The particles of a spherical shape show an error in the method, which depends on the partition of the figure on the dipole. The method allows you to calculate the effect on the optical feedback of the interaction between the timing. The review shows the results of such calculations, both for a pair of particles, and for the clusters of which they are composed. Also, with the aid of the discrete-dipole approximation method, a field in the vicinity of nanoparticles for a real structure is calculated. The calculation showed the existence of a local amplification of the field – “hot spots”. Their existence is confirmed by the experiment.

Key words: plasmonic, modeling, the method of discrete dipoles, local fields, hot spots, fractal clusters, nanoparticles.