Capturing photons with transformation optics

Metallic objects in close contact and illuminated by light show spectacular enhancements of electromagnetic fields due to excitation of surface plasmons, which have the potential for exploitation in ultra sensitive spectroscopy and in nonlinear phenomena. They also play a role in van der Waals forces, heat transfer and non contact friction. The extremes of lengthscales, varying from the micrometre to the subnanometre, challenge direct computational attack. Here we show that transformation optics enables an analytic approach that offers both physical insight and easy access to quantitative analysis. For two metal spheres at various separations we present details of the technique and discuss the optical absorption spectrum, spatial distribution of the modes and the van der Waals forces.