Lu Yi

Performance test of active mirror

Two sets of measurement systems were designed to measure the tip-tilt angles and the frequency response of the active mirror. A CCD laser interferometer measurement system was designed to measure the tip-tilt angles. The mathematical model between the interferogram and the tip-tilt angle was deduced. After preprocessing the interferogram and thinning the fringes, the least square method was used to fit the fringes. Then, based on equal thickness interference principle, the tip-tilt angles of the active mirror were got. The result of angle movement range in X direction is 56.872, and the resolution is 0.113. The result of angle movement range in Y direction is 49.835, and the resolution is 0.112. A photodiode measurement system was designed to test the frequency response of the active mirror. Modulated by the active mirror with triangle waveform signal, a beam of He-Ne laser was focused on a photodiode, and was converted to electrical signal. The electrical signal and the triangle waveform signal were input to an oscilloscope together. Three different frequencys triangle waveform signals, such as 65Hz, 100Hz and 250Hz, were respectively used to test the frequency response of the active mirror. By comparing the input triangle waveform signal with the output electrical signal, the frequency response of the active mirror was got and it was more than 100Hz.