Complete Electromagnetic Dyadic Green Function Characterization in a Complex Environment—Resonant Dipole-Dipole Interaction and Cooperative Effects

The Green function plays a central role in wave propagation, as it describes the response of a system to an arbitrary impulse. However, measuring it experimentally is very challenging since it needs to be measured in both amplitude and phase with deep subwavelength spatial resolution. These highly demanding requirements have significantly limited the experimental attempts towards measuring the Green function in optics.

In a recent Phys Rev X publication, we describe a method to measure both the real and imaginary parts of the Green function by recording the mutual impedance between two dipoles at microwave frequencies. The effectiveness of this approach is demonstrated by the full characterisation of the complex Green function inside a resonant planar cavity of parallel or non-parallel mirrors at a ultrahigh resolution 100x below the wavelength. With this data, we are able to investigate various aspects of resonant dipole-dipole interaction and cooperative effects inside a photonic cavity.

Significance:

- We develop a new general methodology to fully measure the Green function in both amplitude and phase at ultrahigh spatial resolution.

- Our technique provides a powerful way to solve problems for which no analytic solution exists and where numerical simulations demand excessive computational resources.

- We characterize cooperative effects such as superradiance and cooperative Lamb shift inside a cavity which is relevant for various communities such as cavity QED, photovoltaics and nanophotonics.