A system for rapid thermal processing of a substrate in a process chamber while measuring and controlling the temperature at the substrate to establish substantially uniform substrate temperature in real time. The system includes an essentially continuous spirally-configured multizone illuminator having a plurality of substantially concentric rings of heating lamps for directing optical power toward the substrate and a fluid cooled optical reflector facing the substrate frontside and having a relatively high optical reflectivity. The illuminator can also be offset from the geometric center of the substrate. The system can also include a plurality of contact devices to provide thermal conductivity from each, or some subset, of the plurality of heating lamps. The illumination system of the present invention provides improved spatial resolution and improved thermal properties at the heating lamps.