Detecting the Complex Amplitude of Surface Plasmon Polaritons by Leakage Radiation Holographic Microscopy

Detecting the complex amplitude of near-field nonradiative waves is essential in nanophotonics. Scanning-based optical methods can measure amplitude, phase, and polarization of nonradiative waves. To overcome the inherent low speed of scanning, leakage radiation microscopy (LRM) has been developed, but current phase-resolved LRM methods rely on complicated iterative phase retrieval approaches or unstable interference setups. Here, we propose leakage radiation holographic microscopy that records the interferogram between leakage radiation (LR) of surface plasmon polaritons (SPPs) and an unmodulated reflection wave in a stable common-path manner. The complex amplitude of the LR can be numerically reconstructed by off-axis digital holography. It is verified that the reconstructed complex amplitude of LR reveals the properties of the SPP field when interacting with nanoprobes located in the optical near field. Numerical simulations and experimental demonstrations on nanosamples with various geometries, sizes, and materials have verified the validity of the proposed microscopy.