Non-destructive testing with double pulsed laser ESPI

摘要

Electronic Speckle Patten Interferometry (ESPI) (1) is one of the attractive Non-destructive Testing (NDT) technologies. There are two ESPI working modes: addition ESPI mode and subtraction ESPI mode (2). Compared to the disadvantage of the subtraction ESPI mode which strictly requires that there is no movement among the optical parts in an ESPI system, by using the addition ESPI mode, the movement of a measured material is frozen with a short pulsed laser. As a result, the addition ESPI mode is believed to be suitable for the rigorous conditions where the subtraction ESPI mode is inapplicable. Based on the double pulsed laser ESPI work theory, the interference fringe contrast and a simulation method are introduced in this paper. In the simulation, a compound material with a flaw is interrogated. Only when the interference fringe passes through a special electric filter, can the result be obtained, thus the electric filter applied to the experiment needs delicate fabrication. Its quality and central frequency influence the final interference fringe result. Therefore, a series of filters are designed such as band-pass filters and high-pass filters, with a specific method applied. Subsequently, the result of the simulation for NDT with the double pulsed ESPI method is acquired and analyzed.