# Compressing Few-Cycle Optical Near Fields in the Tip–Sample Junction of a Scanning Probe Microscope

## TL;DR

This paper shows how light pulses can be compressed in nanoscale gaps, enabling precise control and study of light at the nanometer scale.

## Contribution

The study introduces subcycle temporal resolution of electric fields in plasmonic nanogaps using visible to near-infrared light.

## Key findings

- Electric field amplitude and phase were measured with subcycle precision in a nanogap.
- A complex-valued local near-field enhancement was observed in the tip-sample junction.
- Spatial confinement in the nanogap correlates with reduced pulse duration of few-cycle light.

## Abstract

Plasmonic nanogaps confine light to dimensions in the
nanometer
or even subnanometer range while simultaneously enhancing the local
electromagnetic field strength. This spatial light confinement has
been key for the development of nano-optics. So far, the temporal
dynamics of such nanoconfined fields has received comparatively little
attention, in particular in the visible spectral range. Here we measure
the amplitude and phase of the electric field of visible to near-infrared
light pulses scattered from the gap between a sharp gold tip and a
metal surface. We retrieve the time structure of the field with subcycle
precision. We provide evidence for a complex-valued local near-field
enhancement and demonstrate that the spatial confinement of a few-cycle
pulse in the investigated nanogap is correlated with a substantial
reduction in its pulse duration. Our results pave the way for probing
the linear and nonlinear electric field dynamics of single quantum
emitters in nanogaps.