Effect of dielectric interface on vector field mapping using gold nanoparticles as a local probe: Theory and experiment

We investigate the influence of an air–dielectric interface on evanescent field vector detections using a gold nanoparticle as a local probe. In particular, we are interested in how the reflected field from the interface modifies the scattered signal, both in its strength and polarization direction depending on the detection angle. Dielectric–air or dielectric–water interface is a most widely used platform to perform single molecule spectroscopy. Knowing the electric field direction that the single molecule experiences is prerequisite for obtaining precise information on that molecule. The far-field scattered signal is derived by solving self-consistently the polarization induced on the gold nanoparticle by the local field and its radiated field in the Green function formalism. The scattered light intensity for each detector polarization direction is obtained by varying the dielectric constant, the distance from the gold nanoparticle to the interface, and the detection angle. The gold nanoparticle is modeled by a single dipole and coupled dipoles, respectively, and comparisons are given. Detection angle dependent far-field measurements are compared with theory, and they are in good agreements. Our study shows that for vector-field mapping on dielectric-interface, an ideal detector angle exists whereby the horizontal and vertical field components can be readily deduced without further correction. For any other detector angles, a correction factor should be taken into consideration to determine local field polarization direction.