| Popis: |
The technique of heterodyne holographic interferometry for the accurate measurement of small displacements is wellestablished. In this paper a new detection method is employed which allows the direct measurement of strain components. This potentially offers an optical, non-contact replacement for the strain gauge, with a resolution of better than one microstrain.In double exposure heterodyne holographic interferometry, a separate reference beam is used for each exposure, andduring reconstruction a phase shift (10kHz in this case) is applied to one of the reference beams. The phase of the beatsbetween the two images is proportional to the displacement between the images. In the technique described in this paper, light from a small region on the two superimposed images is focussed onto closely spaced photodetectors. The phasedifference between the two signals is directly proportional to a component of the strain at that point. The instrument is insensitive to small translational movements of the surface in any direction.The method has been applied to both double exposure and real-time holographic interlerometry, and it has been testedagainst a strain gauge. The results obtained so far show that the technique is a reliable method for measuring strain, withseveral advantages over alternative methods. |
