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A new multi-channel far infrared (FIR) laser interferometer was built up and applied to HL-2A. The unique feature of real-time heterodyne interferometer is the combination of high power radiation source (300 mW), lower noise room temperature detector (noise temperature below 6000 K) with good spatial resolution of 7 cm. Various parameters are optimized for maximum laser output power. Zero crossings of the signals are counted with field programmable gate array (FPGA) digital circuitry yielding the resolution of 1/1000 fringe. The newly measured results including density fluctuation are also presented.

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