Three-dimensional thermal imaging using two-photon microscopy

Thermal processes are important in areas ranging from biological to advanced materials processing. Here, we present a method for measuring temperature profiles in three dimensions using a combination of two-photon microscopy and calibrated temperature-dependent fluorescent dyes, or 'molecular thermometers'. We have found that the dye, tris(2,2'-bipyridine)ruthenium(II) ( ) possesses both a strong temperature dependence in the range 0-60 deg C and a large cross section for two-photon induced fluorescence, making it ideal for two-photon thermal imaging. The technique is used to map out the temperature profile in a thick polyacrylate film containing an embedded wire heater, and, from that, the thermal properties of the polymer are determined.