Imaging Nanoscale Electromagnetic Near-Field Distributions Using Optical Forces

Area of Science:

• Nanoscale imaging
• Optical physics
• Surface science

Background:

• Mapping optical near-fields is crucial for understanding light-matter interactions at the nanoscale.
• Existing methods often lack the required resolution or are limited by background noise.
• Atomic Force Microscopy (AFM) offers a potential platform for high-resolution optical field mapping.

Purpose of the Study:

• To demonstrate the application of AFM for mapping optical near-fields with nanometer resolution.
• To profile electric field distributions of focused laser beams using optical forces.
• To investigate the capabilities of Photo Induced Force Microscopy (PIFM) for sensitive optical imaging.

Main Methods:

• Utilizing a gold-coated AFM probe to detect optical forces between the probe and its image dipole.
• Profiling electric field distributions of focused laser beams with varying polarizations.
• Employing a dipole-dipole interaction model for theoretical predictions and comparisons.
• Investigating optical forces between an AFM probe and a gold nanoparticle.

Main Results:

• Experimentally recorded focal force maps show good agreement with theoretical predictions.
• Successfully estimated the aspect ratio of the AFM probe apex using optical forces.
• Demonstrated that optical forces between the probe and a nanoparticle indicate electric field distribution.
• PIFM achieved background-free, thermal noise-limited imaging from Visible to RF wavelengths.

Conclusions:

• AFM is a powerful tool for nanometer-resolution optical near-field mapping.
• PIFM provides sensitive, background-free imaging of optical phenomena across a wide spectral range.
• The technique is limited only by the AFM probe geometry and performance.