Measurement of Laterally Induced Optical Forces at the Nanoscale

TL;DR

This paper presents a method to measure lateral optical forces at the nanoscale using an AFM, enabling detailed mapping of electric field distributions and potential for multi-channel force detection.

Contribution

The authors developed a novel AFM-based technique to measure lateral optical forces, including engineered cantilever shapes for enhanced sensitivity, and demonstrated agreement with simulations.

Findings

Lateral optical forces can be effectively measured with AFM.

Engineered cantilever shapes improve force detection sensitivity.

The method aligns well with theoretical simulations.

Abstract

We demonstrate the measurement of laterally induced optical forces using an Atomic Force Microscope (AFM). The lateral electric field distribution between a gold coated AFM probe and a nano-aperture in a gold film is mapped by measuring the lateral optical force between the apex of the AFM probe and the nano-aperture. Torsional eigenmodes of an AFM cantilever probe were used to detect the laterally induced optical forces. We engineered the cantilever shape using a focused ion beam to enhance the torsional eigenmode resonance. The measured lateral optical force agrees well with simulations. This technique can be extended to simultaneously detect both lateral and longitudinal optical forces at the nanoscale by using an AFM cantilever as a multichannel detector. This will enable simultaneous Photon Induced Force Microscopy (PIFM) detection of molecular responses with different incident field polarizations. The technique can be implemented on both cantilever and tuning fork based AFMs.