Improved common-path fast-scanning heterodyne interferometer system as potential dense-plasma diagnostics

An improved common-path fast-scanning heterodyne interferometer system has been developed. The mechanical vibration is one of the most critical error sources in typical interferometry system. These errors can be mostly eliminated in a common-path interferometry using a full common-mode rejection scheme. Taking advantage of it, the common-path interferometry is suitable for the measurements in noisy environments and can be applied even to the scanning interferometry. A prototype common-path interferometer system with He-Ne laser has been constructed with the capability of fast scanning by adding a rotating polygon mirror. A test of this system has been completed successfully by measuring the thickness profile of the scratched glass. In this study, the interferometer system is proposed and discussed as a potential density profile diagnostics for dense plasmas. By using a CO2 laser instead of a He-Ne laser, it may also be applied to get the time evolution of steep density profiles of plasma transport barriers in tokamak plasmas