The three deformation components x, y, z of a vibrating object are measured simultaneously by use of digital holography with a double-pulse ruby laser source. The object is illuminated from three different directions, each optically path matched with three reference beams such that three independent digital holograms are formed and added incoherently in one single CCD image. The optical phase difference between the two recordings taken for each hologram is quantitatively evaluated by the Fourier-transform method so that a set of three phase maps is obtained, representing the deformation along three sensitivity vectors. The total object deformation is obtained as a vector resultant from the data of the three phase maps. To give the full three-dimensional (3-D) description, the shape of the object is measured by the two-wavelength contouring method. Experiments are performed with a cylinder as the test object, transiently and harmonically excited. The 3-D deformation and shape measurement results are presented graphically.
"Multidimensional deformation measurement is carried out, thanks to a multidirectional spatial carrier  . Demonstration was performed with simultaneous two- and three- dimensional measurements. Two-or three-noncoplanar sensitivity vectors are necessary. "
[Show abstract][Hide abstract] ABSTRACT: This paper presents the experimental optical analysis of the crack inside an electronic component. The optical setup is used to carry out multidimensional deformation measurements using digital color holography and the spatial multiplexing of holograms. Since the Fresnel transform method depends on wavelength, a wavelength-dependent-zero-padding algorithm is described and results in a rigorous sizing of each reconstructed monochrome image. The criterion to optimize the parameters is presented and is based on minimizing the widening of the impulse response of the full recording/reconstruction process. The application of the proposed method is illustrated through the analysis of the mechanical deformation of the electronic component, and offers keys to understand its failure mode in industrial conditions.
Optics and Lasers in Engineering 11/2011; 49(11):1335-1342. DOI:10.1016/j.optlaseng.2011.05.018 · 2.24 Impact Factor
"This all-electronic version of holographic interferometry is called pulsed TV holography or, more commonly, today, digital holographic interferometry. This technique has been used in many applications such as transient deformation measurements, acoustic field measurements and combustion studies     . "
[Show abstract][Hide abstract] ABSTRACT: Pulsed digital holographic interferometry has been used to study the shock wave induced by a Q-switched Nd–YAG laser (λ = 1064 nm and pulse duration 12 ns) on a polycrystalline boron nitride (PCBN) ceramic target under atmospheric air pressure. A special setup based on using two synchronized wavelengths from the same laser for processing and measurement simultaneously has been introduced. Collimated laser light (λ = 532 nm) passed through the volume along the target and digital holograms were recorded for different time delays after processing starts. Numerical data of the integrated refractive index field were calculated and presented as phase maps showing the propagation of the shock wave generated by the process. The location of the induced shock wave front was observed for different focusing and time delays. The amount of released energy, i.e. the part of the incident energy of the laser pulse that is eventually converted to a shock wave has been estimated using the point explosion model. The released energy is normalized by the incident laser pulse energy and the energy conversion efficiency between the laser pulse and PCBN target has been calculated at different power densities. The results show that the energy conversion efficiency seems to be constant around 80% at high power densities.
Journal of Physics D Applied Physics 10/2008; 41(21):215502. DOI:10.1088/0022-3727/41/21/215502 · 2.72 Impact Factor
"Schnars and Juptner were among the first to perform digital holography with a CCD camera (1994). Later on, similar techniques have been applied to various areas including holographic interferometry (Schedin et al. 1999), holographic microscopy (Zhang and Yamahuchi 1998), and biomedical imaging (Boyer et al. 1996). "
[Show abstract][Hide abstract] ABSTRACT: We present a digital in-line holographic PIV system for diagnosing 3D particulate flows. This system records in-line holograms directly to a CCD camera and reconstructs them numerically. Since the pixel resolution of CCD cameras is much lower than that of holographic films, conventional particle extraction methods cannot yield high depth resolution that is important for velocity measurement and particulate flow diagnostics. To solve this problem, we have developed a novel particle extraction method based on the complex amplitude of reconstructed wave. With a simple in-line recording setup, this method can reach a depth resolution that is comparable with that of some off-axis holographic PIV systems. This method also alleviates the speckle noise problem intrinsic to in-line particle holography since speckles and particles can be clearly differentiated in complex wavefield. This technique is the basis for a digital in-line holographic PIV (HPIV) system with the addition of Concise Cross Correlation (CCC) and particle pairing algorithm (Pu and Meng 2000). Details of the system hardware and data processing method are described in this paper. The system was tested by both a simulated 3D flow around a collapsing spherical cavity and a laboratory particle suspension.
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