Application Research Of Noise Reduction And Vibration Measurement For The Principle Of Shearing Interferometry

Shearing interferometry is an important method in optical measurement, which is widely applied in the detection of optical system or device, research of liquid and gas flow, measurement of stress and strain in experimental mechanics, analysis of vibration and other fields. The principle of shearing interferometry is using interference between the measured wavefront and its own transformed wavefront.Vibration measurement has a generally application in bridges, buildings, machinery and some other fields. There are two main ways to measure the vibration using the method of time-average digital holography:the vibration measurement of intensity and phase, both of them are based on the reconstructed image and the reconstructed wave field. The detection of amplitude distribution of the traditional time average holography is realized using the reconstructed image intensity distribution. However, dissatisfaction results can be obtained only by relying on light intensity distribution to determine on amplitude distribution, as there exists some noise influences such as speckle noise. Theoretical analyses show that the reconstructed optical field of time average holography is modulated by the first kind of zero-order Bessel function. The result of time average holographic reconstructed field divided by reconstructed field without any vibrating can get only Bessel function carrying phase information. As there are only two values of the phase of the first kind of zero-order Bessel function, namely0and π, we can determine the amplitude distribution through the reconstructed field phase. And this method is better than that of the traditional, but it takes a longer time. This paper presents a new method which uses the shearing principle to vibration measurement of time average digital holograph, shearing interferometry form the principle is to use of wave surface by measuring its own after some transform wavefront for interference. We can detect the amplitude distribution rapidly by directly using the shearing interferogram to find out the phase stepping region, Interference in the dark stripe should only be appeared in the corresponding phase jump locations. This is a very good way to avoid the effect of noise, by interference fringe contrast high and fine, and this method needs no phase unwrapping operation. So the time that is occupied by the machine can greatly shorten, is better than the traditional method of measuring vibration method. Simulation computation and experiment results show that the time of the new method needs for vibration measurement is shorter than that of reconstructed field phase, and the measurement effect is better than that of reconstructed image intensity.The phase of optical field obtained by optical interferometry using denoising operation, and current denoise algorithms can achieve appreciable results when the phase of optical field changes slowly. If the phase has high spatial variation frequency, the conventional denoise algorithms often cause defection of phase detail and fringe breaks. For this reason, a new denoise algorithm and corresponding theoretical analysis is proposed in this paper, which separates the speckle noise from optical field by introducing shearing of optical field. Simulative computation and experimental results demonstrate that the new algorithm is feasible and effective, and it can obtain noticeable result compared with conventional algorithms when the phase of optical field has high spatial variation frequency.