Survey of interferometric techniques used to test JWST optical components

JWST optical component in-process optical testing and cryogenic requirement compliance certification, verification & validation is probably the most difficult metrology job of our generation in astronomical optics. But, the challenge has been met: by the hard work of dozens of optical metrologists; the development and qualification of multiple custom test setups; and several new inventions, including 4D PhaseCam and Leica Absolute Distance Meter. This paper summarizes the metrology tools, test setups and processes used to characterize the JWST optical components.