Lightpipe for high temperature substrate processing

A substrate processing system comprising:

• a processing chamber;
• and
• an optical pyrometer assembly, disposed within the processing chamber, to measure an emitted thermal radiation originating substantially from a portion of a target surface, the optical pyrometer assembly comprising:
• a lightpipe that comprises a core and a hollow sheath surrounding the core, the core and the sheath being concentric with one another, wherein the sheath is formed by a chemical vapor deposition process and includes local protrusions within a hollow interior and along an inner surface thereof to maintain a position of the core within the sheath, wherein the core includes a plurality of local recessed areas formed within an outer surface of the core at locations of the local protrusions such that for each local protrusion there is one corresponding local recessed area formed adjacent to a corresponding local protrusion;
• wherein a temperature of the target surface is determined from an intensity of a portion of the measured emitted thermal radiation near at least one wavelength.