A Scanning Cavity Microscope

TL;DR

This paper introduces a scanning cavity microscope that significantly enhances optical signals, enabling ultra-sensitive imaging of nanosystems' absorption and dispersion properties beyond traditional limits.

Contribution

The authors develop a scanning optical microcavity technique that achieves 1700-fold signal enhancement, allowing quantitative and potentially super-resolution imaging of nanomaterials.

Findings

1700-fold signal enhancement over diffraction-limited microscopy

Sensitivity below 1 nm² for gold nanoparticle extinction cross section

Potential for sub-diffraction spatial resolution using higher order cavity modes

Abstract

Imaging of the optical properties of individual nanosystems beyond fluorescence can provide a wealth of information. However, the minute signals for absorption and dispersion are challenging to observe, and only specialized techniques requiring sophisticated noise rejection are available. Here we use signal enhancement in a scanning optical microcavity to demonstrate ultra-sensitive imaging. Harnessing multiple interactions of probe light with a sample within an optical resonator, we achieve a 1700-fold signal enhancement compared to diffraction-limited microscopy. We demonstrate quantitative imaging of the extinction cross section of gold nanoparticles with a sensitivity below 1 nm2, we show a method to improve spatial resolution potentially below the diffraction limit by using higher order cavity modes, and we present measurements of the birefringence and extinction contrast of gold nanorods. The demonstrated simultaneous enhancement of absorptive and dispersive signals promises intriguing potential for optical studies of nanomaterials, molecules, and biological nanosystems.