Visibility enhancement of carrier fringes in Electronic Speckle Shearing Pattern Interferometry using microspheres for light detection in back reflection

Abstract We report on the visibility enhancement in Electronic Shearing Speckle Pattern Interferometry (ESSPI) using carrier fringes and back reflected light from microspheres sticked to the surface of the object under test. Microspheres increase reflectivity in the direction of the light source and have been used recently for light detection when high-speed cameras are used in transient analysis but their specific influence on fringe visibility has remained unknown. To investigate the microspheres influence on fringe visibility, three objects were analyzed; two of them with microspheres sticked to its surface with different mean sizes of 10.2 μm and 157.5 μm, and a third one covered with white developer. Using carrier fringes and the first order peak of the Fourier transform of the carrier fringe, the visibility figures reported herein show that there is an enhancement of visibility values with microspheres of 10.2 μm for small shears. Advantages and disadvantages of the use of microspheres sticked to the object's surface in ESSPI are discussed.