Optimized near-field optical response via adaptive tip illumination

TL;DR

This paper introduces an adaptive wavefront shaping method using Zernike modes to optimize near-field optical responses in tip-enhanced microscopy, significantly boosting signal intensity and robustness.

Contribution

It presents a practical, optics-based adaptive control strategy for near-field enhancement, combining aberration correction and field engineering in tip-enhanced spectroscopy.

Findings

Near-field signal improved by 1.4 times with conventional optimization.

Further 5 to 15 fold enhancement achieved with Raman-band based optimization.

Zernike-mode control effectively corrects aberrations and enhances field confinement.

Abstract

The performance of tip-enhanced optical microscopy is often limited by inefficient coupling of the excitation field to the plasmonic tip apex, as well as by thermal drift and optical aberrations. Here, we demonstrate that adaptive wavefront shaping based on Zernike mode provides a practical approach to achieving robust near-field optimisation at the tip apex. Using a sequential feedback algorithm, initially using the near-field signal, we narrow the illumination point-spread function and suppress sidelobes. This demonstrates that Zernike-mode control can be used for both aberration correction and field engineering. In tip-enhanced Raman measurements of a Janus MoSSe monolayer, conventional near-field optimisation increases the signal intensity by around 1.4 fold. A second optimisation step based directly on the Raman-band intensity yields a further 5 to 15 fold enhancement, depending on the specific tips used. These results establish a systematic, optics-based strategy for optimising tip fields, providing a transferable framework for improving tip-enhanced and related near-field spectroscopies.