Simultaneous measurement of out-of-plane displacement and slope using a multiaperture DSPI system and fast Fourier transform.

Department of Physics Applied Optics Laboratory, Indian Institute of Technology Madras, Chennai, India.
Applied Optics (Impact Factor: 1.69). 09/2007; 46(23):5680-6. DOI: 10.1364/AO.46.005680
Source: PubMed

ABSTRACT The simultaneous quantitative measurement of out-of-plane displacement and slope using the fast Fourier transform method with a single three-aperture digital speckle pattern interferometry (DSPI) arrangement is demonstrated. The method coherently combines two sheared object waves with a smooth reference wave at the CCD placed at the image plane of an imaging lens with a three-aperture mask placed in front of it. The apertures also introduce multiple spatial carrier fringes within the speckle. A fast Fourier transform of the image generates seven distinct diffraction halos in the spectrum. By selecting the appropriate halos, one can directly obtain two independent out-of-plane displacement phase maps and a slope phase map from the two speckle images, one before and the second after loading the object. It is also demonstrated that by subtracting the out-of-plane displacement phase maps one can generate the same slope phase map. Experimental results are presented for a circular diaphragm clamped along the edges and loaded at the center.

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