Surface Profile Determination by Additive-Subtractive Phase Modulated ESPI with Fourier Analysis

摘要

An interferometric system for the determination of surface shape or height profiles of engineering components is presented. The system is based on additive-subtractive phase modulated electronic speckle pattern interferometry (AS-ESPI) and works successfully in harsh environmental conditions. Determination of profiles is achieved via repetitively changing the optical pathlength difference (OPD) between two interference beams in the ESPI setup. As the repetition rate is much higher than that of the video frame refreshing, one can remove random environmental noises that are normally of much lower frequency than the repetition rate by the use of speckle decorrelation and frame averaging procedures. Due to the nature that carrier fringes are automatically generated by the OPD change (namely tilting the illumination angle of the object beam), Fourier transform approach is employed to extract the phase data. A simplified method for calculating the surface height (profile) is described and the results are compared to an exact solution. Quantitative measurement results obtained under rather noisy conditions for several components are presented.