Embodiments described herein include integrated systems used to directly monitor a substrate temperature during a plasma enhanced deposition process and methods related thereto. In one embodiment, a substrate support assembly includes a support shaft, a substrate support disposed on the support shaft, and a substrate temperature monitoring system for measuring a temperature of a substrate to be disposed on the substrate support. The substrate temperature monitoring system includes a optical fiber tube, a light guide coupled to the optical fiber tube, and a cooling assembly disposed about a junction of the optical fiber tube and the light guide. Herein, at least a portion of the light guide is disposed in an opening extending through the support shaft and into the substrate support and the cooling assembly maintains the optical fiber tube at a temperature of less than about 100° C. during substrate processing.