Enhanced spontaneous emission of electric dipole by nano-optical antenna

We study the characteristics of nano-optical antenna made of two gold nano-particles by three dimensional numerical calculations at visible and near infrared band. To carry the computational burden and guarantee the precision and speed of a 3D FDTD calculation, adaptive mesh refinement technology is used. We first highlight the concrete way of controlling over the emitter position to fulfill the requirements of larger spontaneous emission enhancement. By exciting the resonance of surface plasmon polaritons (SPPs), we find that the far field directivity is strongly influenced and obtain around 5000-fold spontaneous emission enhancement. Choosing the incident wavelength of 600nm, we compute the decay rates and radiant efficiency as a function of antenna geometry limitations, showing the particle with an aspect ratio of L/R=4 is best for enhancing spontaneous emission. Furthermore, we proceed a spectrum analysis and find an exact relationship between the particle length and resonant wavelength.