Abstract
We demonstrate the application of Atomic Force Microscopy (AFM) for mapping optical near-fields with nanometer resolution, limited only by the AFM probe geometry. By detecting the optical force between a gold coated AFM probe and its image dipole on a glass substrate, we profile the electric field distributions of tightly focused laser beams with different polarizations. The experimentally recorded focal force maps agree well with theoretical predictions based on a dipole-dipole interaction model. We experimentally estimate the aspect ratio of the apex of gold coated AFM probe using only optical forces. We also show that the optical force between a sharp gold coated AFM probe and a spherical gold nanoparticle of radius 15 nm, is indicative of the electric field distribution between the two interacting particles. Photo Induced Force Microscopy (PIFM) allows for background free, thermal noise limited mechanical imaging of optical phenomenon over wide range of wavelengths from Visible to RF with detection sensitivity limited only by AFM performance.
Highlights
Atomic Force Microscopy (AFM)[1], enables high resolution imaging of the physical[1], chemical[2], magnetic[3], and electrostatic[4] properties of materials at the nanoscale
We map the interaction forces between a gold sphere of radius 15 nm and a gold coated AFM probe illuminated by an incident electric field
The origin of optical forces in Photo Induced Force Microscopy (PIFM) can be well understood by modeling the sample under measurement as a sub-wavelength ma→gneto-d →ielectric nanoparticle and the tip of the AFM probe as a sub-wavelength magneto-d→ielectri c→nanoparticle
Summary
Atomic Force Microscopy (AFM)[1], enables high resolution imaging of the physical[1], chemical[2], magnetic[3], and electrostatic[4] properties of materials at the nanoscale. Near-field Scanning Optical Microscopy (NSOM) has been used to study light-matter interaction beyond the diffraction limit with important applications in many areas of nano-optics, materials science, chemistry and biology[11] Both aperture NSOM (a-NSOM)[12] and aperture-less or scattering NSOM (s-NSOM)[13] techniques have been used to map the nanoscale electric[14,15,16,17] and magnetic[18,19,20] field distributions. By detecting the optical force between a gold coated AFM probe illuminated by a tightly focused laser beam and its image induced on a clean glass substrate, we are able to map the electric field distributions within the focal region. → F opt is the time-averaged optical force on the AFM probe tip due to its interaction with the incident field and particle dipole
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