Julia Lobera

Digital speckle pattern interferometry as a holographic velocimetry technique

In this paper digital speckle pattern interferometry (DSPI) as a digital image plane holography (DIPH) technique is presented and its potential for fluid velocimetry are discussed. The recording is carried out with a spatial phase shifting (SPS) DSPI set-up, which can also be viewed as an off-axis DIPH set-up. A theoretical study of both SPS–DSPI analysis using a Fourier transform method and DIPH analysis is presented for a set-up with only one illuminated plane. From the DIPH analysis, a way to extend the SPS–DSPI set-up to simultaneously record but independently reconstruct several fluid planes is inferred. Some preliminary results from a convective flow illustrate the feasibility of the quasi 3D recording.

A comparison of temporal, spatial and parallel phase shifting algorithms for digital image plane holography

This paper investigates the performance of several phase shifting (PS) techniques when using digital image plane holography (DIPH) as a fluid velocimetry technique. The main focus is on increasing the recording system aperture in order to overcome the limitation on the little light available in fluid applications. Some experiments with small rotations of a fluid-like solid object have been used to test the ability of PS-DIPH to faithfully reconstruct the object complex amplitude. Holograms for several apertures and for different defocusing distances have been recorded using spatial phase shifting (SPS) or temporal phase shifting (TPS) techniques. The parallel phase shifted holograms (HPPS) have been generated from the TPS holograms (HTPS). The data obtained from TPS-DIPH have been taken as the true object complex amplitude, which is used to benchmark that recovered using the other techniques. The findings of this work show that SPS and PPS are very similar indeed, and suggest that both can work for bigger apertures yet retain phase information.

Application of DSPI to detect inhomogeneous heating on superconducting ceramics

This paper presents the first application of digital speckle pattern interferometry (DSPI) to detect inhomogeneous heat generation on a superconducting ceramic at cryogenic temperatures. The light scattered by the object is recorded with a CCD camera at the same time as a smooth reference beam. Comparison of two non-simultaneous frames provides information about the out-of-plane deformation field. Spatial phase shifting is used in order to get a good quality fringe pattern. The technique has been applied as a non-destructive evaluation of the performance of ceramic high temperature superconducting materials. DSPI allows the determination of the point where a hot spot will be generated with heating levels that do not deteriorate the sample properties. An excellent agreement between DSPI hot spot location and the position of the melting point that appeared in a destructive experiment has been obtained.

Shifted knife-edge aperture digital in-line holography for fluid velocimetry

We describe a digital holography technique that, with the simplicity of an in-line configuration, produces holograms where the real and virtual images are completely separated, as in an off-axis configuration. An in-line setup, in which the object is imaged near the sensor, is modified by placing a shifted knife-edge aperture that blocks half the frequency spectrum at the focal plane of the imaging lens. This simple modification of the in-line holographic configuration allows discriminating the virtual and real images. As a fluid velocimetry technique, the use of this aperture removes the minimum defocusing distance requisite and reduces the out-of-plane velocity measurement errors of classical in-line holography. Results with different test objects are shown.

High performance computing for Optical Diffraction Tomography

This paper analyses several parallel approaches for the development of a physical model of Non-linear ODT for its application in velocimetry techniques. The main benefits of its application in HPIV are the high accuracy with non-damaging radiation and its imaging capability to recover information from the vessel wall of the flow. Thus ODT-HPIV is suitable for microfluidic devices and biofluidic applications. Our physical model is based on an iterative method which uses double-precision complex numbers, therefore it has a high computational cost. As a result, High Performance Computing is necessary for both: implementation and validation of the model. Concretely, the model has been parallelized by means of different architectures: shared-memory multiprocessors and graphics processing units (GPU) using the CUDA device.

Parallel resolution of the 3D Helmholtz equation based on multi‐graphics processing unit clusters

The resolution of the 3D Helmholtz equation is required in the development of models related to a wide range of scientific and technological applications. For solving this equation in complex arithmetic, the biconjugate gradient (BCG) method is one of the most relevant solvers. However, this iterative method has a high computational cost because of the large sparse matrix and the vector operations involved. In this paper, a specific BCG method, adapted for the regularities of the Helmholtz equation is presented. This BCG is based on the implementation of a novel format (named ‘Regular Format’) that allows the storage of the large sparse matrix involved in the sparse matrix vector product in a compact form. The contribution of this work is twofold: (1) decreasing the memory requirements of the 3D Helmholtz equation using the ‘Regular Format’ and (2) speeding up the resolution of the equation using high performance computing resources. A hybrid Message Passing Interface (MPI)‐graphics processing unit CUDA GPU parallelization that is capable of solving complex problems in short time has carried out (Fast‐Helmholtz). Fast‐Helmholtz combines optimizations at Message Passing Interface and GPU levels to reduce communications costs and to improve the exploitation of GPU architecture. This strategy makes it possible to extend the dimension of the Helmholtz problem to be solved, thanks to the relevant reduction of memory requirements and runtime. Copyright

Two-dimensional quantification of the corrosion process in metal surfaces using digital speckle pattern interferometry

The applicability of digital speckle pattern interferometry (DSPI) to the analysis of surface corrosion processes has been evaluated by studying the evolution of an Fe surface immersed in sulfuric acid. This work describes the analysis process required to obtain quantitative information about the corrosion process. It has been possible to evaluate the corrosion rate, and the results agree with those derived from the weight loss method. In addition, a two-dimensional analysis has been applied, showing that DSPI measurements can be used to extract information about the corrosion rate at any region of the surface.

From ESPI to Digital Image Plane Holography (DIPH): Requirements, Possibilities and Limitations for Velocity Measurements in a 3-D Region

The present work shows how the SPS-ESPI recordings can alternatively be analysed as Digital Image Plane Holographic (DIPH) recordings. When the SPS-ESPI recordings are analysed using a DIPH analysis, both the phase and intensity can be independently retrieved at each point of the fluid plane. The three velocity components in a fluid plane could be measured, since the phase maps detect an out-ofplane velocity component while the intensity data can be analysed with standard PIV methods to detect the two in-plane components. Finally, more than one fluid plane have been simultaneously recorded but independently reconstructed using DIPH. Some preliminary results from a convective flow with a He-Ne laser illustrate these features. A discussion of the requirements , possibilities and limitations of multiple plane DIPH is also presented.

Dual holographic interferometry for measuring the three velocity components in a fluid plane

A technique that allows one to measure simultaneously the three velocity components in a fluid plane is presented. One obtains the quantitative information from only one holographic recording by combining two different reconstruction processes. As both processes use an interferometric comparison of two waves, we refer to this technique as dual holographic interferometry. The far-field fringe pattern that is obtained when reconstruction is made with an expanded laser beam allows one to determine the in-plane velocity components. The image-field fringe pattern that is obtained when a pointwise laser beam is used for reconstruction contains information about an out-of-plane velocity component. As the two reconstruction processes have different sensitivities, two different ways to combine them are proposed. The system has been demonstrated in a fluidlike solid object and in a convective flow.

High performance computing for a 3-D optical diffraction tomographic application in fluid velocimetry

Optical Diffraction Tomography has been recently introduced in fluid velocimetry to provide three dimensional information of seeding particle locations. In general, image reconstruction methods at visible wavelengths have to account for diffraction. Linear approximation has been used for three-dimensional image reconstruction, but a non-linear and iterative reconstruction method is required when multiple scattering is not negligible. Non-linear methods require the solution of the Helmholtz equation, computationally highly demanding due to the size of the problem. The present work shows the results of a non-linear method customized for spherical particle location using GPU computing and a made-to-measure storing format.