Notes on Picophotonics Lecture

Introduction

• Speaker: Works for University of Southampton and NTU Singapore
• Topic: Picophotonics – seeing and studying picometric scale events optically.

Imaging Technologies Overview

• Electron and optical microscopy resolutions are limited to several tens of picometers.
• New imaging and metrology techniques allow entry into the "no man's land" beyond current limitations.
• Focus on picometer imaging using free electron beams.

Free Electron Beam Imaging

• Concept:
  • Focus electron beam on nanoscale objects (e.g., cantilevers) in a scanning electron microscope (SEM).
  • Rate of secondary electron production is position-dependent and can detect displacements as small as one picometer.
• Imaging Technique:
  • Instead of scanning across structures, keep electron beam fixed and detect secondary electrons over time.
  • Calculate modulation spectrum to create hyperspectral images.
• Example: Observing a flea's setae and their movements using this technique.

Brownian Motion Detection

• Importance of studying Brownian motion in nanoscale structures.
• Example of a cantilever and its thermal motion.
• Brownian motion amplitude can be in the range of picometers to hundreds of picometers.
• Characteristic trace of cantilever motion shows both thermal and ballistic regimes.
  • Ballistic motion observed in short time frames, transitioning to random motion.

Optical Techniques in Metrology

• Focus on metamaterials for optical measurements.
• Metamaterials can have their optical properties changed by mechanical movements.
• Brownian motion detection in optomechanical metamaterials shows oscillations around 100-200 picometers.
• Optical detection through changes in reflectivity/transmission of light.

Challenges of Optical Metrology

• Traditional optical measurement limitations due to diffraction limits (e.g., size of the atom vs. wavelength).
• Solution: Using structured, topologically structured light to improve resolution.
• Concepts of singularities and local k-vectors in structured light can lead to resolutions much smaller than the wavelength.

Artificial Intelligence in Optical Measurement

• AI techniques can enhance optical measurement resolution via deep learning.
• Training sets based on diffraction patterns can improve the estimation of parameters like the width and position of slits in metallic films.
• Results show optical measurement resolutions comparable to electron microscopy techniques.

Recent Advances in Nanostructure Measurements

• Use of topologically structured light to detect scatter from nanowires.
• Improvement in training sets leads to better accuracy in detecting displacement.
• Recent results: ability to measure displacements as small as 28 picometers, aiming for under 2 picometers.
• Potential applications include studying dynamics of Brownian motion in nanostructures.

Conclusions

• Highly trained AI networks can solve complex measurement problems in picophotonics.
• Topological illumination and sensitivity are key to achieving high resolutions in optical metrology.
• Future work includes studying fundamental physics at picometric scales and potential biomedical applications.

Q&A Session Highlights

• Clarification on collision time related to internal Brownian motion.
• Discussion on the relation to x-ray interferometry and the complexity of current advanced systems versus new optical methods.