Interferometry is an optical measuring method with the character of non-destructive, high sensitivity and high accuracy. However, its measurement range is limited by the phase ambiguity. Hence the method with two separate different wavelengths light source is introduced to enlarge the measurement range.
As for the two-wavelength interferometry case, phase shifting is the traditional way to acquire the phase map, it needs to repeat the measurement twice, which means the measurement cannot be accomplished in real time. Hence to solve the problem, a temporal sequence interferometry has been used. This method can obtain the desired phase information in real time by using the Fourier transform methods of the interferogram recorded in a sequence while the object is being deformed. But, it is difficult to retrieve the phase information directly due to the multi extreme points in one period of the cosine function.
In this paper, an algorithm based on the wavelet ridge analysis is adopted to retrieve the two wavelength phase fluctuation caused by the displacement simultaneously.
The preliminary experiment is conducted and the results are compared with theoretical simulations to validate the proposed approach. The laser emits light with two wavelengths 532 nm and 473 nm, two separated interference patterns in time sequence are detected by the CCD camera in the same time. The overlapped interferograms of two colors are analyzed by this algorithm and the corresponding phase information are obtained. The maximum error value between the simulation and theory is 0.03 um and the relative error is 0.33%.
In this paper, a ridge algorithm which is based on wavelet analysis is adopted in the measurement of in-plane displacement. To measure in-plane displacement by electronic speckle pattern interferometry (ESPI), a series of speckle patterns are captured with the help of a CCD camera which is known as temporal speckle pattern interferometry (TSPI) technique and TSPI technique has better correlation and a larger measuring range compared with ESPI technique. To retrieve the phase fluctuation caused by the displacement of specimen, three types of complex wavelets are selected in the wavelet analysis to compare with the traditional Fourier analysis.