We describe a novel noninvasive method to measure temperature profiles during processing. A key feature is the use of a temperature-sensitive fluorescent dye that is incorporated into the polymer resin at dopant levels. By monitoring spectral features of this dye, we can effectively measure its temperature. A focusing technique that we call "confocal fluorescent optics" then allows us to measure the temperature as a function of position into the resin. We present results of critical tests of the device. Namely we test the spatial resolution and its ability to measure a linear temperature profile in a quiescent polymer. Finally, we present the first on-line temperature profile measurements, carried out in a circular die at the exit of a twin screw extruder. Temperature gradients on the order of 5 degrees C/mm in a polyethylene resin are observed between the outer wall and the center of the die.