Embodiments of the invention provide a method and an apparatus for detecting the temperature of a substrate surface. In one embodiment, a method for measuring the temperature is provided which includes exposing the surface of the substrate to a laser beam radiating from a laser source, radiating emitted light from a portion of the surface of the substrate, through the shadow ring, and towards a thermal sensor, and determining the temperature of the portion of the surface of the substrate from the emitted light. The substrate may be disposed on a substrate support within a treatment region and a shadow ring may be disposed between the laser source and the surface of the substrate. The shadow ring may be selectively opaque to the laser beam and transparent to the emitted light.