Near infrared large aperture (24 inches) interferometer system development

In the past twenty years, our group has developed a series phase-shifting Twyman-Green or Fizeau interferometers. We also developed the simultaneous phase-shifting interferometrer system and the aspherical test system based on CGH, etc. One of our recent works presented in this paper is to develop a near infrared (1055nm) large aperture (24 inches) interferometer which is the first NIR large aperture interferometer in China. It can be used to test the optical element with large aperture, including surface flatness, refractive index homogeneity, etc. The difficulties existed are as follows. Firstly, as the apertures of the optical elements are large, the influence of the stress and temperature on the materials should be considered. Secondly, the alignment of the optical path is difficult as the light is invisible. Thirdly, the demand of the manufacture, test of the large aperture elements and the aligning of the overall system is very strict.