Mechanical test study in composites using digital holographic interferometry and optical coherence tomography simultaneously.

A dual optical configuration to inspect the internal and external mechanical response of a composite specimen is presented. The inspection simultaneously uses two equally aligned optical techniques, digital holographic interferometry and Fourier domain optical coherence tomography, to retrieve surface and internal data, respectively. The sample under study is a composite specimen of poly-methyl-methacrylate reinforced with metallic particles. Two different sets of samples are analyzed to compare their mechanical behavior. A homemade, fully controlled testing machine is used to apply a controlled compression load while each technique registers an image. In this form, the surface and internal optical phase measurements are correlated to the same compression value for comparison purposes. Results for each technique are directly presented as simultaneous displacement maps, and a discussion and conclusion of this proposed dual method of inspection are presented.

Cortical bone quality affectations and their strength impact analysis using holographic interferometry.

It is now accepted that bone strength is a complex property determined mainly by three factors: quantity, quality and turnover of the bone itself. Most of the patients who experience fractures due to fragility could never develop affectations related to bone mass density (i.e. osteoporosis). In this work, the effect of secondary bone strength affectations are analyzed by simulating the degradation of one or more principal components (organic and inorganic) while they are inspected with a nondestructive optical technique. From the results obtained, a strong correlation among the hydroxyapatite, collagen and water is found that determines the bone strength.

Interferometric study on birds' feathers.

Optical techniques such as speckle pattern interferometry are well known in the nondestructive testing measurement community. They can be used, for instance, as a predictor of the mechanical behavior of a sample under study. However, in almost all circumstances, a mathematical model has to be applied in order to make sense of these measurements. This is a critical issue when an organic sample is studied, mainly due to its complex deformation response. A good example of this is observed in the birds' feathers. They have extraordinary mechanical and aerodynamic properties thanks to their stiffness and lightness. A couple of live birds are safely situated in front of an out-of-plane sensitive digital holographic interferometer (DHI), an optical system capable of recovering the optical phase in this type of nonrepeatable or unpredictable experiment. In order to recover the backscattering signal and its interferometric response, several images are recorded from different sections of the plumage. Displacement maps are obtained from what is, as far as is known, the first time that full field microdisplacement maps are presented over a hummingbird and a parakeet plumage.

Simultaneous measurement of in-plane and out-of-plane displacement fields in scattering media using phase-contrast spectral optical coherence tomography.

The use of phase-contrast spectral optical coherence tomography to measure two orthogonal displacement components on a slice within a scattering medium is demonstrated. This is achieved by combining sequential oblique illumination of the object and recording two interferograms before plus two after the deformation. The proposed technique is illustrated with results from a sample undergoing simple shear. Depth-resolved out-of-plane and in-plane sensitivities of 0.14 and 4.2 microm per fringe are demonstrated up to a depth of 400 microm in a water-based polymer.

Double-shot depth-resolved displacement field measurement using phase-contrast spectral optical coherence tomography.

We describe a system for measuring sub-surface displacement fields within a scattering medium using a phase contrast version of spectral Optical Coherence Tomography. The system provides displacement maps within a 2-D slice extending into the sample with a sensitivity of order 10 nm. The data for a given deformation state is recorded in a single image, potentially allowing sub-surface displacement and strain mapping of moving targets. The system is based on low cost components and has no moving parts. The theoretical basis for the system is presented along with experimental results from a simple well-controlled geometry consisting of independently-tilting glass sheets. Results are validated using standard two-beam interferometry. A modified system was used to measure through-the-thickness phase changes within a porcine cornea due to displacements produced by an increase in the intraocular pressure.

Very high speed cw digital holographic interferometry.

It is reported for the first time the use of a very high speed camera in digital holographic interferometry with an out of plane sensitivity setup. The image plane holograms of a spherical latex balloon illuminated by a cw laser were acquired at a rate of 4000 frames per second, representing a time spacing between holograms of 250 microseconds, for 512 x 512 pixels at 8 bits resolution. Two types of tests were accomplished for a proof of principle of the technique, one with no constrains on the object which meant random movements due to non controlled environmental air currents, and the other with specific controlled conditions on the object. Results presented correspond to a random sample of sequential digital holograms, chosen from a 1 second exposure, individually Fourier processed in order to perform the usual comparison by subtraction between consecutive pairs thus obtaining the phase map of the object out of plane displacement, shown as a movie.