Fig. 8: Photothermal absorption spectroscopy and imaging.

a Schematics of the setup employed for photothermal absorption spectroscopy and imaging. Inset (left): diagram of the thermal shift induced by the photothermal absorption of gold nanoparticles. Inset (right): scanning electron microscopy (SEM) image of a silica microtoroid. Scale bar: 10 μm⁶². b Large-area maps of a silica-on-silicon toroid (left) and an all-glass toroid (right). c Photothermal imaging of a single gold nanorod on an all-glass microtoroid. Inset (top): SEM image of a nanorod with a scale bar of 100 nm. Inset (bottom): high-resolution photothermal imaging of the nanorod⁶⁴. a Reprinted with permission from ref. ⁶² [Nature Publishing Group]; b, c Reprinted with permission from ref. ⁶⁴ [John Wiley & Sons, Inc.]