# Harnessing evanescent photoacoustic waves for multi-domain imaging

## TL;DR

This paper introduces a new imaging technique using evanescent photoacoustic waves to enhance photoacoustic microscopy capabilities.

## Contribution

The novel use of evanescent photoacoustic waves in microscopy enables new functionalities like surface reconstruction and edge detection.

## Key findings

- Evanescent PA waves can be generated and detected in PAM by positioning samples near an interface.
- Supercritical angle PA signals show intensity dependence on source depth and symmetric angular patterns.
- A proof-of-concept SA-PAM system demonstrates surface topography reconstruction and edge detection.

## Abstract

Photoacoustic microscopy (PAM) offers a non-invasive imaging method that overcomes the limitations of light scattering in biological tissues by visualizing optical contrast through the detection of photo-generated acoustic signals. While optical microscopy has significantly advanced through the exploration of optical evanescent waves, the potential of evanescent photoacoustic (PA) waves in PAM remains largely unexplored. In this work, we demonstrate the generation and detection of evanescent PA waves in PAM by positioning the sample near an interface, which directs these waves into the far-field beyond the supercritical angle (SA). These SA-PA signals exhibit distinct characteristics, including dependence of intensity on the source depths and symmetry in far-field angular patterns. Leveraging these features, we develop a proof-of-concept for supercritical angle photoacoustic microscopy (SA-PAM), which utilizes evanescent PA waves to enable new PAM functionalities, such as surface topography reconstruction and edge detection. This approach highlights the role of acoustic near-field exploration in advancing PA technology.