Instantaneous wavefront measurement of large aperture optical elements


Optical interferometry is based on measuring, recording and calculating of the fringes of superposed coherent beams. The regular optical measurement is relatively, which introduces a relatively deviation of the tested flat from the reference flat. When the precision of the two flats matches, an unnegligible error will be introduced. This problem has become one of the bottlenecks of manufacturing of high precision optical component. In order to solve the problems and calibrate the reference surface of large diameter interferometer with high precision, the point diffraction interferometer method is studied. In this method, the regular reference is replaced by the spherical wave, which is introduced by the diffraction of the spot light. So, it has some unique advantages, like high precision, simple construction, anti-interference, and the result is the true value of the testing flat. 
  The team of ChenLei in Nanjing University of Science and Technology has proposed a method based on the structure of oblique incidence of reflective searing point diffraction interferometer. A lateral displacement between the reference wavefront and the test wavefront is formed after passing this structure. The shear of two beams introduces linear spatial carrier frequency to the point diffraction interferogram. After receiving a good contrast interferogram, it is retrieved by Fourier Transform (FT) automatically. The optical path is up to 20m, so the air current is a significant factor to the result. Also because of the air current, the system itself can be seen as an instantaneous wavefront happening and measurement of large aperture optical elements. The results indicate that the root mean square value is in accord with that acquired by SID4 wavefront sensor, (less than λ/50). So, the method proposed can be applied to instantaneous wavefront measurement about high resolution and accuracy.

About the Team
The team of researcher ChenLei is affiliated to the department of Optical Engineering, the school of Electronic and Optical Engineering, Nanjing University of Science and Technology. Based on the principle of optical interference, the principle and technique of measuring various physical quantities of laser in optical measurement are studied. Also, the research of high precision digital laser interferometer, laser tachymeter and optical attitude measuring instrument and other precision optical systems are studied. In recent years, we have completed the project supported by the National Defense Basic Scientific Research program” XXX Transient Wavefront Test and Calibration Technology Research”, the project supported by the National Natural Science Foundation of China” Large-Caliber Optical Components Key Detection Technology Research and Verification Research”, the National major scientific instrument development project” Development of Key Components and Software Systems for Phase Modulation and Detection”, the project supported by NSFC-Astronomy Joint Fund” Research on Non-Contact Measurement of Short Coherent Light Microscopic Interferometry and Arm-Shaped Profiler”, China Academy of Engineering Physics Development project” Phase Shift Diffraction Interferometer” and so on. The research group has won the second prize of national science and technology progress twice, the first prize of provincial science and technology progress award three times, the second prize four times, the third prize four times and the thirteenth challenge cup grand prize, and so on.



Meng S, Chen L, Zhu W H, et al. Instantaneous wavefront measurement of large aperture optical elements[J]. Opto-Electronic Engineering, 2018, 45(1): 170627.