13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- the investigation surface with amplitude increasing in time. The solid curve represents the theoretically calculated output voltage signal. Figure 4. Theoretical curves of behavior output signal u(t) at the increasing amplitude of the investigation surface 3.1. Assessment of range of measurements From the analysis of Eq. (10) and (11) follows that change of output voltage from minimum to the maximum corresponds to displacements of the investigation surface at a value equal λ/4. Then, when demonstrate the constant direction - not sign-variable - for determination of value of full movement it is enough to define number of changes of the output single from maximum to the minimum. At sign-variable movements that corresponds to vibration loadings, character of an output signal of the photodetector has features. The analysis of Eq. (10) and (11) shows that at vibrations of the investigation surface with amplitudes it is less or equally λ/8 the output voltage of the photodetector corresponds to a form of vibrations of this surface. With amplitudes of vibrations of the investigation surface more λ/8 the output voltage of the photodetector won't correspond to a form of vibrations of this surface that as it is visible in Fig. 4. In this case development of additional algorithm of interpretation of an output signal of the photodetector is required. For registration of vibrations without additional processing of an output signal, as appears from Eq. (10) and (11), it is necessary to choose φ(0) equal 2 1 2 n (where n=0,1,2…). This condition means that at the initial moment of measurements output voltage from the photodetector has to be established so that its value corresponded to value equal: A u u u 2 (0) min max (12) It is reached by corresponding change of a phase of the reference beam. Under these conditions amplitude B of measured vibrations of the investigation surface will correspond to value equal λ/8. 4. Results and conclusion Realization of this method, based on the analysis of change of intensity of the single speckle, was used for the investigation of wave processes in a plate subjected shock loading. Fig. 4 shows the
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