Research On High Precision Small Plane Interferometric Testing Technique

The high precision surface detection of the optical element is the goal of optical detection areas. Current foreign high-precision detection reaches a high level mostly through the phase-shift interferometry technique, which require high-precision phase-shifting devices, the corresponding calibrating method of phase-shifting error, which are deficiency in domestic interferometer. In order to ensure the high accuracy algorithm advantages of phase-shifting interferometry, while avoiding the complex errors of phase-shifting devices, the article puts forward a virtual digital phase-shifting technique based on the structure of Fizeau interferometer that does not require hardware devices. This technology avoids the hardware phase-shifting error, ensures the accuracy of the phase shift, suitable for various aperture optical flats detection. The main contents of this paper are:Firstly, the principle of Fizeau Interferometer, the phase-shifting interferometry principle, key factors affecting the phase-shifting interference measurement and basic principles of virtual digital phase-shifting are discussed; Then, by using Matlab software simulation, the detection accuracy of four-step phase-shifting algorithms together with the Fourier transform algorithm and the virtual digital phase-shifting algorithm in phase extraction technology are analysed. Simulation of φ50mm caliber plane (PV value for 0.0473λ, RMS values for 0.0112 λ), processed by the virtual digital phase-shifting method to obtain the shape (PV value 0.0496λ, RMS values for 0.0112λ). The PV value of the surface residual is 0.005λ, the RMS value is 0.00037λ, It can reach a high precision inspection requirements.Because the filtering problem will be introduced in the process of digital phase-shifting, this paper proposed a simplified digital fringe superimposition technique which only need extracting the filter frequency of positive and negative spectrum to realize the phase shift. So this method can avoid the errors in spectrum move and simplified the process of frequency extraction. The simulated experiments verify the correctness of this method, which also owns a simple and effective frequency extraction characteristics.ZYGO interferometer measured plane acquired interference patterns is processed using virtual digital phase-shifting algorithm. The PV value of the measured surface is 0.231λ according to virtual digital phase shift method and the corresponded RMS value is 0.034λ. The PV value and the RMS value of the measured surface that is obtained by ZYGO Laser Interferometer are 0.216λ and 0.017 λ.Through measurement of sample, and the system error analysis in the process, the algorithm is proved to achieve a high-precision in phase detection, and also, this method is suitable for the component surface production site detection.