Mapping Nanoscale Electromagnetic Near-Field Distributions Using Optical Forces

We demonstrate the application of Atomic Force Microscopy (AFM) based optical force microscopy to map the optical near-fields with nanometer resolution, limited only by the AFM probe geometry. We map the electric field distributions of tightly focused laser beams with different polarizations and show that the experimentally measured data agrees well with the theoretical predictions from a dipole-dipole interaction model, thereby validating our approach. We further validate the proposed technique by evaluating the optical electric field scattered by a spherical nanoparticle by measuring the optical forces between the nanoparticle and gold coated AFM probe. The technique allows for wavelength independent, background free, thermal noise limited mechanical imaging of optical phenomenon with sensitivity limited by AFM performance. Optical forces due to both electric and magnetic dipole-dipole interactions can be measured using this technique.