Multifrequency Excitation and Detection Scheme in Apertureless Scattering Near Field Scanning Optical Microscopy

TL;DR

This paper introduces a multifrequency excitation and detection method in apertureless near field optical microscopy that significantly enhances sensitivity and resolution, enabling complete phase and amplitude retrieval of near field signals.

Contribution

It presents a novel multifrequency scheme that improves sensitivity, resolution, and background suppression in apertureless near field microscopy, with potential for non-interferometric phase and amplitude measurements.

Findings

Twofold sensitivity improvement

Deep sub-wavelength resolution of λ/230

Enhanced background suppression capabilities

Abstract

We theoretically and experimentally demonstrate a multifrequency excitation and detection scheme in apertureless near field optical microscopy, that exceeds current state of the art sensitivity and background suppression. By exciting the AFM tip at its two first flexural modes, and demodulating the detected signal at the harmonics of their sum, we extract a near field signal with a twofold improved sensitivity and deep sub-wavelength resolution, reaching $\lambda/230$. Furthermore, the method offers rich control over experimental degrees of freedom, expanding the parameter space for achieving complete optical background suppression. This approach breaks the ground for non-interferometric complete phase and amplitude retrieval of the near field signal, and is suitable for any multimodal excitation and higher harmonic demodulation.