Optical technologies towards improving the Far-infrared laser Polarimeter-Interferometer system on HL-2A tokamak

•The optical setup integrated by a lens and a high-sensitivity Pyroelectric Array Camera was applied to the alignment of the HCOOH laser in HL-2APolarimeter-Interferometer (PIer) system.•Spurious intermediate frequency (IF) mixed in the interferometry beat signal was verified in practice, and can be effectively eliminated by using a special adjustment method, based on the single-polarization response characteristic of the Schottky diode detector.•Spurious oscillation mixed in the Faraday rotation angle on HL-2A was verified to be mainly caused by the feedback lights reflected from the detector surface.•Experimental results on HL-2A validated that the unwanted feedback lights can be suppressed by employing the optic-isolator which was composed of a polarizer and a quarter-wave plate.