Making the invisible visible!

The way we apprehend our world is obviously determined by the fact that what we observe is visible or not! This is also true for observing light emitted from molecules or atoms. Whilst numerous optical transitions are possible between the different energy levels of such a molecule or atom, many of these transitions never show up since they are forbidden by symmetry rules. However, when the surrounding of the emitter (atom, molecule) is modified, these symmetry rules are modified and transitions that were previously forbidden and invisible, become perfectly visible!

Recently, we have investigated the mediation of symmetry-forbidden atomic transitions using plasmonic nanostructures. We have shown that the excitation of the electric dipole-forbidden, quadrupole-allowed 6 2S1/2 − 5 2D5/2 transition in cesium may be enhanced by more than 6 orders of magnitude in the intense, inhomogeneous near field of a plasmonic nanoantenna. Using optical reciprocity, the enhancement can be understood to apply to spontaneous emission as well, allowing the fast and efficient optical detection of excited atoms.

This image shows the quadrupole transition rate enhancement at points 1 nm above the surface of the left arms of resonantly excited gold nanoantennas with gap sizes of g = 5 (top) and 25 nm (bottom). Values are displayed using an equirectangular representation.

This work has important implications for the realization of future atomic clocks; additional information is available in the corresponding publication:

Check the corresponding publication: PDF External link: doi: 10.1103/PhysRevA.85.022501