End-Scope-Type Laser Speckle Strain/Damage Inspection System Using Optical Fiber

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Important issues on the development of an end-scope type laser speckle strain/damage monitoring system are both to minimize a laser light path and to extract an out of plane component in the rigid translation.In the laser speckle measurement, a laser light path needs approx. 300mm at least. Thus the mirror reflection technique was developed to compact the system size.The extraction of the rigid translation was achieved by the development of 4sensor laser speckle strain measurement system. In 4-sensor system, four sensors were set on the inclined line with an angle of 45 deg. Horizontal and vertical speckle displacements in each sensor were available to extract and distinguish all translation and rotation components and normal strains and shear strain. Furthermore, the same technique was applicable to the one sensor system by using an area division method with one sensor.Using the above techniques, it was found that the principle of the end-scope type speckle sensor was accomplished and completed.