Faraday-Effect Polarimeter-Interferometer System for current density measurement on EAST

A multichannel far-infrared laser-based \textbf{PO}larimeter-\textbf{INT}erferometer (\textbf{POINT}) system utilizing the three-wave technique is under development for current density and electron density profile measurements in the EAST tokamak. Novel molybdenum retro-reflectors are mounted in the inside wall for the double-pass optical arrangement. A Digital Phase Detector with 250 kHz bandwidth, which will provide real-time Faraday rotation angle and density phase shift output, have been developed for use on the POINT system. System time response ($\sim$ 1 microsecond) and phase resolution (\textless 0.1$^{\circ})$ allows resolution of fast equilibrium changes associated with MHD events. Initial calibration indicates the electron line-integrated density resolution is less than 5 $\times$ 10$^{16}$m$^{-2}$ ($\sim$ 2$^{\circ}$), and the Faraday rotation angle rms phase noise is \textless 0.1$^{\circ}$. Initial results of POINT system will be presented.