Very Long Plasmon Oscillation Lifetimes in the Gap Between Two Gold Particles

A small gap between metal nanoparticles provides a strong local field enhancement when illuminated with light. This local field enhancement has proven to be very useful to enhance the response in Raman spectroscopy and may even contribute to increased efficiency in solar cells. Here, the nature of the field enhancement and the effect on the optical absorption spectrum has been identified by measuring the electro-magnetic fields within and outside the nanoparticle gap. Time resolved measurement of the electric field component showed that the plasmon resonance within the gap lives much longer than the excitation pulse duration. These results elucidate the optical properties of the plasmonic gap and provide ideas for future research.