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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-µm 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 p m / H z 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.

In this work, using a custom-built Spectral-domain optical coherence tomography microscopy setup we measured expansion caused by heat dissipation during fluorescence emission in dye-doped polystyrene microspheres with 70 pm sensitivity.