Dual-beam symmetric illumination-observation TV holography system for measurements
TL;DR: In this article, instead of observing along the optical axis, the scattered light along the direction of the illumination beams, and imaged it as two separate images onto the photo sensor of a CCD camera, was used for real-time evaluation of in-plane displacement components as well as surface shape.
Abstract: The Leendertz dual-beam symmetric illumination-normal ob- servation arrangement is widely employed for real time evaluation of in-plane displacement components as well as surface shape. Instead of observing along the optical axis, we have examined the Leendertz ar- rangement by observing the scattered light along the direction of the illumination beams, and imaged it as two separate images onto the photo sensor of a CCD camera. The interferometer is a combination of two channels, each of which measures independently and simulta- neously the information pertaining to either the in-plane displacement component of a deformation vector, or the surface relief variation of a three-dimensional object. In addition, a summary of possible measure- ments that can be carried out from the present arrangement is also high- lighted. Experimental results using a four-frame phase shifting technique are illustrated. © 2001 Society of Photo-Optical Instrumentation Engineers.
...While the arrangement  senses the in-plane displacement with sensitivity proposed by Leendertz , the one described in [11,12] yields two-fold increase in sensitivity....
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