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