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...

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Bibliographic Details
Published in:Fusion engineering and design 2018-12, Vol.137, p.137-142
Main Authors: Li, Y.G., Zhou, Y., Ding, W.X., Li, Y., Wang, H.X., Yi, J., Deng, Z.C., Yuan, B.S., Yao, K., Yu, L.M., Zhang, Y.P., Huang, Z.H., Shi, Z.B., Liu, Yi, Yang, Q.W., Xu, M., Duan, X.R.
Format: Article
Language:English
Subjects:
Diode detectors
Far infrared radiation
Faraday effect
Feedback
HL-2A
Infrared lasers
Interferometry
Intermediate frequencies
Lasers
Optical properties
Polarimeter-interferometer
Polarimeters
Polarizers
Schottky diodes
Spurious IF
Spurious oscillation
Tokamak devices
Wave plates
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Summary:•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. Since the first performance of the HCOOH laser Polarimeter-Interferometer (PIer) in 2015 HL-2A experimental campaign, several optical technologies have been applied to improve the PIer system, including: (1) Optical alignment of the HCOOH laser at the long distance was implemented by the optical setup integrated by a lens and a high-sensitivity Pyroelectric Array Camera. (2) Due to application of the orthogonal waves transmission in the PIer system, some spurious intermediate frequency (IF) might be generated in the interferometry beat signal. For this problem, an effective optical adjustment method based on the single-polarization response characteristic of the Schottky diode detector was summarized in practice. (3) For double-passing type Faraday-effect polarimeter, analysis indicated that the severe oscillation disturbance in Faraday rotation angle was mainly caused by the stray lights or the feedback lights. Experimental results on HL-2A successfully validated that the unwanted feedback lights mainly came from the detector surface and was able to be effectively suppressed by the optic-isolator which was composed of a polarizer and a quarter-wave plate.
ISSN:0920-3796
1873-7196
DOI:10.1016/j.fusengdes.2018.09.003