UC Irvine

The objective of this dissertation is to develop a novel method to measure nanoscale optical field distribution using optical induce forces. We demonstrate the application of Atomic Force Microscopy (AFM) for detecting nearfield optical induced force including axial force and lateral force. We develop a method that detects laterally and axially induced optical forces by different flexure and torsional modes which can enable simultaneous multi-channel detection of nanoscale optical forces along different orientations.

We have mapped 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 in axial force of tightly focused laser beams with different polarizations. The experimentally recorded focal force maps agree well with theoretical predictions based on the 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.

We also show a controlled method to fabricate tips that have high enhancement factor, which is desirable for the linear and non-linear response of the molecule response.

Photon 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. The use of an AFM cantilever as a multi-channel detector paves the way for simultaneous PiFM detection of molecular responses with different incident field polarizations.