Two‐color interferometry for fusion plasma diagnostics

Radial view interferometers on large fusion devices have experienced difficulty in compensating for large vibration‐induced phase shifts. This compensation has previously been achieved using common path visible or near infrared interferometers. However, the high rate of phase change observed by the compensation interferometer combined with deterioration of reflecting surfaces located close to the harsh plasma environment limit the resolution and usefulness of such systems. This article describes laboratory tests of a vibration‐compensating interferometer that operates at two wavelengths of the CO2 laser: 9.2 and 10.6 μm. It is particularly well suited for application to CIT or other devices with either high density or large plasma dimensions.