Abstract: Methods and an apparatus for providing a non-contact probe for accurately measuring the temperature of a substrate in a process chamber are disclosed. One exemplary apparatus is a processing chamber, which includes a heating source, where the heating source heats the substrate. Also included is a window maintained at a substantially constant temperature. The window allows only a first wavelength spectrum of energy emitted from the heating source to pass. In addition, the window isolates the heating source from an internal region of the processing chamber. A probe configured to detect a second wavelength spectrum of energy emitted directly from the substrate is included. The energy emitted directly from the substrate corresponds to a temperature of the substrate, and the temperature of the substrate is provided to the controller, which adjusts an intensity of the heating source based on a set point temperature for the substrate.