Vector field mapping of local polarization using gold nanoparticle functionalized tips: independence of the tip shape

We have measured local electric field vectors of local polarizaton on the nanoscale using gold nanoparticle functionalized tips as local field scatterers. In our experiments, the local field induces a dipole-moment in the gold nanoparticle functionalized tip, which then radiates into the far-field, transferring the full information about the local electric field from the near into the far field. The polarization characteristics of the scattered fields are analyzed using a conventional ellipsometry method. The tip dependent scattering function- the polarizability tensor- is fully determined by far field scattering measurements. Once the polarizability tensor for each tip is correctly accounted for in the data analysis, our results show that the finally determined local field polarization vectors are essentially independent of the tip shape.