High-temperature optical probe

A probe body comprising:

• a. a measurement tube having a plurality of probe vents adapted to allow process fluid to flow therethrough;
• b. two or more purge rings, each comprising:
• i. a process window;
• ii. a purge gas inlet;
• iii. a plurality of purge gas outlet openings adapted to direct purge gas toward or adjacent to the process window;
• iv. an inner ring and an outer ring, wherein the inner ring comprises a portion that extends and fits within an outer wall of the outer ring;
• and
• c. a measurement region defined by a portion of the measurement tube and the two or more of the purge rings;
• wherein the probe body is capable of withstanding temperatures up to and including about 1100° C.;
• and
• wherein the probe body is adapted for insertion into a chamber or piece of equipment for measuring a desired condition.