Recent Progress on dispersion interferometers for nuclear fusion and low-temperature plasmas

A dispersion interferometer (DI) is known to be less sensitive to mechanical vibrations, which is one of the main sources of error for conventional interferometers. A simple optical configuration is also one of the advantages of the DI approach. Since the first application of a homodyne DI on a nuclear fusion plasma device in the 1990s, several interferometer techniques have improved the operation of the DI. Improvements in nonlinear crystals have also improved the performance and availability of the DI. Immunity to neutral gas density changes, which is needed for low-temperature plasma measurements, is also found. A remaining challenge is the suppression of the offset drifts, which can be significant. Recent studies confirmed that they are caused by ambient humidity changes.