The effect of the camera resolution on fringe patterns in electronic shear speckle pattern interferometry

Abstract

An electronic speckle pattern interferometry system is an Optic,-electronic hybrid system, in which laser speckle field is used to carry the information of a object under test to the photoelectric target of television camera in the system, which transforms the speckle signal into video signal, then the video signal is transmitted to a television monitor after being processed by the following elec- tronic processor, at last a speckle fringe pattern is displayed on the screen of the monitor, which shows the displacement or the deformation of the object. In the ES PI system, the camera is a key device because it connects optical method with electronic method. Unfortunately, the camera usu- ally can not resolve the fine detail of the speckle field, for example, if the numerical aperture (NA) of lens is 16, and the wavelength of the laser 0.63 pm, then the maximum spatial frequency of the speckle field on the image plane of the system is 99 mm-1 (1) , while the size of pixel of the target of a industrial camera is about 20pm, which is approximately equivalent to 50 mm-1 in sampling fre- quency. Therefore, it is significant to study such a problem: how does the resolution of the camera effect on the ES PI fringe patterns?