Accurate quantification of photothermal heat originating from a plasmonic metasurface.

Photothermal effect in plasmonic nanostructures (thermoplasmonic), as a nanoscale heater, has been widely used in biomedical technology and optoelectronic devices. However, the big challenge in this effect is the quantitative characterization of the delivered heat to the surrounding environment. In this work, a plasmonic metasurface (as a nanoheater), and a Fabry-Perot (FP) cavity including liquid crystal (as a thermometer element) are integrated. The metasurface is manufactured through a bottom-up deposition method and has a near perfect absorption that causes an efficient temperature rising in the photothermal experiment under a low intensity of irradiation ($0.25\; {\rm W}/{{\rm cm}^2}$0.25W/cm). Generated heat from the metasurface dissipates to the liquid crystal (LC) layer and makes a spectral shift of FP modes. More than 50°C temperature elevation with accuracy of 1.3°C are measured based on the consistency of anisotropic thermo-tropic data of the LC and a spectral shift of FP modes. The calculated figure of merit (FoM) of the constructed device, which indicates the temperature sensitivity, is 22. The FoM is four times more than other reported thermometry devices with broad spectral width. The device can be also used as an all-optical device to control the plasmonic resonance spectrum.