Optical temperature mapping around plasmonic structures using directional anisotropy in fluorescence

Optically measuring temperature fields around plasmonic structures is of great importance for their thermal management considering the strong energy dissipations along with the extraordinary abilities of light coupling. Among all the available methods, ratiometric studies are particularly desirable since they suppress the influence of trivial factors, such as temporal fluctuations in excitation and spatial non-uniform distributions of fluorescent species, and thus gives reliable temperature dependence. Here we report a new ratiometric thermometry that simultaneously captures the fluorescence images of different numerical apertures (NAs) to resolve the temperature-dependent orientations of emission dipoles. This thermometry measures fluorescent anisotropy based on the directionality of emission. We show that this thermometry can be used to measure temperature near metallic surfaces. We foresee it to trigger interests of a large community who desire simultaneous thermal characterization along with the optical imaging. Moreover, it brings out a general idea to simplify ratiometric setups if inequalities exist on the excitation side, which may reach for a larger number of researchers.