Application of a high-precision interferometric measuring system as phasing the segmented primary mirrors of the next generation of ground-based telescope

Abstract

Optical telescope systems with segmented mirrors require precise coalignment of their segments to achieve the desired full near-diffraction-limit performance. The segment vertical misalignment (piston error) between the segments must be reduced to a small fraction of the wavelength (<100nm) of incoming light. We have considered an interferometric piston error measurement system based on a high-aperture Michelson interferometer layout for accomplishing such objectives, The piston error between the segments can be extracted from the interferometric fringes mismatching, The innovation introduced in the optical design of the interferometer is the simultaneous use of monochromatic light and two-wavelength combination white-light source in a direct method for improving the central fringe identification in the white-light interferometric phasing system. We find that this two-wavelength combination technique can greatly increase the visibility difference between the central fringe and its adjacent side fringes, and thus it offers an increased signal resolution. So make the central fringe identification become easier, and enhance the measure precision of the segment phasing error. As a result, it is suitable for high-precision measurement purpose and application in the segment piston error phasing system.