13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- 2. 2 Measurement system Realization of this method, based on the analysis of change of intensity of the single speckle, for measurement of dynamic processes in solid mechanics it is offered to carry out according to the optical scheme presented in Fig. 3. By means of optical system L2 the rough surface of a research object O is lighted with laser radiation and is focused on the CCD TV. Let's emphasize, that as it was noted above, in the plane of a CCD matrix the image of object covered speckles is fixed. That allows to record on CCD TV a image of the research object with binding speckles to concrete points of this object. If to direct the reference beam (in Fig. 3 it isn't shown) on a CCD matrix, as a result, we will receive standard the digital speckle interferometer which allows to make measurements of displacements with restrictions indicated in Introduction. Figure 3. Optical scheme for dynamic measurement Measurement of dynamic processes in solid mechanics is offered to be carried out according to the analysis of change of intensity of the single speckle. Standard CCD matrixes, as a rule, aren't the high-speed photodetector. Therefore they aren't capable to register of change of intensity of the single speckle in the wide frequency range. For overcoming of this restriction in the optical scheme it is offered to use in addition the high-speed photodetector PD, allowing to analyze of intensity of the single speckle in the wide frequency range. For allocation single speckle, by means of the beam splitter BS2 the image of the single speckle goes on an entrance end face of an optical fiber OF2 which output end face is agreed with the high-speed photodetector PD. Diameter of a core of an optical fiber of OF2 has to be agreed with the transversal size of a speckle, that is the ratio (Eq. 6) has to be carried out. For creation of a reference beam by means of the beam splitter BS1 the part of radiation of the laser L goes on an entrance end face of an optical fiber OF1 which output end face is also agreed with the high-speed photodetector FD. The output ends of optical fibers OF1 and OF1 are combined so that conditions (Eq. 6 and Eq. 7) were satisfied. The change of intensity of the single speckle is registered by the photodetector PD and is recorded in the PC for processing and visualization. 3. Theory Let's consider for the offered optical scheme formation of distribution of intensity in the single speckle when performing conditions (Eq. 6 and Eq. 7). Let's write down values of vectors of electric intensity on the photodetector PD for waves passed through both optical fibers in the following kind:
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