Article

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.

0 Bookmarks
 · 
67 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents a spatial phase-shift digital shearography system based on a modified Michelson Interferometer, which is capable of measuring out-of-plane deformation and its first derivative simultaneously. A reference beam is introduced into the Michelson Interferometer using an optical fiber. Two sheared images from the Michelson Interferometer are combined with the reference beam to generate two holograms and one shearogram. The Fourier Transform method is utilized to calculate the phase difference. To separate the spectrum in the Fourier Domain, the reference beam is tilted a small angle to create a spatial phase shift. An out-of-plane deformation and its first derivative can then be determined simultaneously from a single speckle interferogram by properly selecting filters for the spectrum image. The theory and the experimental results are presented.
    Optics Communications 01/2013; 286:277–281. · 1.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A direct method of determining second-order derivatives of displacement (curvature and twist) using two-channel double-aperture digital shearography is presented. Spatial carrier fringes are incorporated inside the speckle using a double-aperture mask in a two-channel experimental setup. Two sets of slope phase maps are generated that are either shifted in the x direction for curvature measurement or in the y direction for twist measurement. Experimental results are presented to verify the validity of the proposed method.
    Optical Engineering 01/2010; 49(3). · 0.96 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we report the investigations undertaken towards mapping the slope of specularly reflecting bent plates using moiré deflectometry. Towards improvement of the measurement characteristics, the four-step phase shifting technique has been incorporated into the deflectometric setup to obtain quantitative results. The experimental verification of the proposed technique for poly-methyl methacrylate (PMMA) specimens in the form of a cantilever beam and a circular plate, subjected to a well-defined load, has been undertaken. In each case, the experimental results match well with theoretical predictions.
    Journal of Modern Optics 01/2012; · 1.16 Impact Factor