Sub-nanometer measurement of transient structural changes in dye-doped polystyrene microspheres

TL;DR

This paper introduces an interferometric spectral-domain optical coherence tomography method to measure nanometer-scale transient structural changes in dye-doped polystyrene microspheres, enabling insights into elastic and inelastic responses of microscopic objects.

Contribution

It demonstrates a highly sensitive optical technique for detecting sub-nanometer size changes in microspheres induced by dye molecule energy release.

Findings

Achieved 0.4 pm/√Hz sensitivity in size change measurement.

Detected elastic and inelastic responses of microspheres.

Potential application in measuring biological cell-sized objects.

Abstract

We present an interferometric spectral-domain optical coherence tomography microscopy setup to detect structural changes using interference of light reflected from different interfaces of the sample. We induce a reproducible nanometer-scale size change in dye-doped 10$~\mu$m polystyrene microspheres by the release of Stokes shift energy of dye molecules inside the microspheres, excited by a modulated 532-nm laser. The resulting optical path length difference was measured with a sensitivity of 0.4$~pm/\sqrt{Hz}$ limited by photodetection noise, and reveals elastic as well as inelastic responses, which opens up possibilities for measuring the response of cell-sized biological objects.