# Atomic-Scale Optical Microscopy with Continuous-Wave Mid-Infrared Radiation

## TL;DR

This paper introduces a new method for high-resolution optical microscopy using mid-infrared lasers to achieve atomic-scale imaging.

## Contribution

The study demonstrates atomic-scale optical imaging using continuous-wave mid-infrared lasers, a novel approach compared to traditional methods.

## Key findings

- Optical signals modulated on Ångstrom length scales were observed using continuous-wave mid-infrared lasers.
- Near-field optical tunneling emission (NOTE) was achieved under continuous-wave driving, typically requiring high-intensity laser pulses.
- Anharmonic tip oscillation effects on the signal were identified and strategies to mitigate them were proposed.

## Abstract

Understanding matter at the most fundamental level requires
optical
microscopy with ever-higher spatial resolution. Scanning near-field
optical microscopy (SNOM) has enabled important advances, circumventing
the diffraction limit of light by confining it to the apex of a sharp
metallic tip. However, the mesoscopic tip geometry restricts the spatial
resolution to the nanometer scale. Here, using a conventional tabletop
continuous-wave mid-infrared laser and intensity-based detection we
observe optical signals modulated on Ångstrom length scales,
consistent with light emission from atomically confined tunneling
currents. The emergence of near-field optical tunneling emission (NOTE)
 considered a strong-field excitation process  under
continuous-wave driving is remarkable, as it typically requires ultrashort
high-intensity laser pulses. Further, we find that anharmonic tip
oscillation can influence the signal and propose strategies to mitigate
this effect. Our findings enable the use of this tunneling-mediated
contrast mechanism with standard optical setups, establishing a pathway
to optical imaging with unprecedented resolution.