Figure 21.

Transducers for localized photothermal spectroscopy: optical transducer based on WGM resonators. Adapted with permission from ref (200). Copyright 2016 Springer Nature. Panel (a) illustrates the shift of the Lorentzian-shaped fiber transmission spectrum of a WGM upon switching of the probe beam and the consequent heating of the resonators material via absorption by the analyte. Panel (b) depicts the optical setup and the pump–probe scheme utilizing double modulation. The top inset shows a SEM micrograph of a microtoroidal resonator (scale bar 10 μm).