Introduction to Optical Metrology

5.2.16 ELECTRONIC SPECKLE PATTERN INTERFEROMETRY

The speckle size in speckle interferometry can be controlled by the F# of the imaging lens. Further, in a two-aperture arrangement, the size can be doubled by adding a reference beam axially. It is thus possible to use electronic detectors, which have limited resolution, for recording instead of photographic emulsions. Use of electronic detectors avoids the messy wet development process. Further, the processing is done at video rates making the technique almost real time. The photoemulsions, as mentioned earlier, integrate the light intensity falling on them. In speckle techniques with photographic recording, the two exposures were added in succession, and then techniques were developed to remove ...