Optical aligning and measuring methods for large aperture optical system

How to implement high accuracy measurement of large-aperture coaxial optical system is crucial to the optical alignment and optical property evaluation. The methods of image quality measurement including interferometer-collimating testing, wave front testing by using Hartmann, image processing and analysis of out-of-focus image were introduced. Both the advantages and disadvantages of the three methods were compared, which showed that the alignment method based on interferometer-collimating testing is the one with the highest accuracy. The method of computer-aided alignment (CAA) based on interferometer-collimating was discussed in detail. By using a ZYGO interferometer, interferograms with different field of views and a series of Zernike coefficients were obtained to express the disalignment of the system, and then these incorrect parameters were calculated by CAA algorithms. An alignment experiment of coaxial three-mirror system with 4m focal length and 500mm aperture was carried out. The RMS value of the system is lower than 0.07. after iterations, which is close to the optical diffraction limit, proving the effectiveness of CAA method in alignment guidance.