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Surface Imaging with optically trapped probes

Background: Photonic Force Microscopy (PFM) is a competing technique to Atomic Force Microscopy (AFM), where the thin tip of a mechanical cantilever is scanned across the surface to obtain a high-resolution height profile. With a much higher sensitivity and an easily adjustable trapping stiffness, the PFM can generate surface height profiles using an optically trapped probe.
Problem:The interferometric tracking signals of the probe's axial displacements are massively distorted by phase disturbances of the surface structure.
Approach: We use two optical laser foci that scan side by side across the structured surface: one with a 190nm small optically trapped probe and the other focus without a particle. By subtracting both interferometric signals from each other and extracting the high energy fluctuations, we can recover the surface height profile with a resolution beyond the optical diffraction limit.


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