Temperature mapping using molecular diffusion based fluorescence thermometry via simultaneous imaging of two numerical apertures.

We report a new optical technique to map two-dimensional temperature distributions in liquid solutions based on the thermal motion of fluorescent molecules. We simultaneously capture the fluorescence images of different numerical apertures (NAs) to resolve the temperature-dependent orientations of emission dipoles. In this work, we use two numerical apertures (2NA) prove the concept. This 2NA technique is robust against the intensity variations caused by photobleaching, unsteady illumination and nonuniform molecule distribution. Moreover, as the measured intensity of directional emission is insensitive to polarization changes, this method can be applied to polarizing materials, such as metal surfaces. Under this configuration, the 2NA technique offers another advantage of naturally filtering out the emission background that falls out of collection cones. We foresee the 2NA technique to open a new detection scheme of fluorescence thermometry.