Scanning plasmonic microscopy by image reconstruction from the Fourier space

Area of Science:

• Nanophotonics and Plasmonics
• Optical Microscopy Techniques
• Materials Science

Background:

• Near-field scanning optical microscopy (NSOM) is limited by diffraction.
• Leakage-radiation microscopy (LRM) captures plasmonic light but often suffers from resolution limits.
• Existing methods struggle to resolve fine details in nanoplasmonic structures.

Purpose of the Study:

• To develop a high-resolution imaging technique for nanoplasmonic structures.
• To overcome the resolution limitations of conventional NSOM and LRM.
• To enable imaging solely from evanescently coupled light.

Main Methods:

• Implemented a Fourier lens within a near-field scanning optical microscope (NSOM).
• Operated the microscope in the leakage-radiation microscopy (LRM) mode.
• Reconstructed images from collected plasmonic 'forbidden' light in Fourier space.

Main Results:

• Achieved significantly enhanced spatial resolution in imaging.
• Demonstrated a resolution enhancement factor of approximately 4 compared to direct real-space imaging.
• Successfully imaged a sub-wavelength annular slit in a gold film using a nanodiamond tip.

Conclusions:

• The developed method offers a simple yet powerful scheme for high-resolution nanoplasmonic imaging.
• Reconstruction from Fourier space effectively removes resolution-limiting far-field light.
• This technique provides a substantial improvement over existing optical microscopy methods for nanoscale structures.