Amalia Martínez

Three-dimensional deformation measurement from the combination of in-plane and out-of-plane electronic speckle pattern interferometers

An optical setup that can be switched to produce in-plane and out-of-plane sensitivity interferometers was designed for three-dimensional deformation measuring by electronic speckle pattern interferometry. Divergent illumination is considered in the evaluation of sensitivity vectors to measure both in-plane and out-of-plane displacement components. The combination of these interferometers presents the advantage of greater sensitivity in directions u, v, and w than a typical interferometer with three illumination beams provides. The system and its basic operation are described, and results with an elastic target that is exposed to a mechanical load are reported.

Self-healing property of a caustic optical beam

It is well known that Bessel beams and the other families of propagation-invariant optical fields have the property of self-healing when obstructed by an opaque object. Here it is shown that there exists another kind of field distribution that can have an analog property. In particular, we demonstrate that a class of caustic wave fields, whose transverse intensity patterns change on propagation, when perturbed by an opaque object can reappear at a further plane as if they had not been obstructed. The physics of the phenomenon is fully explained and shown to be related to that of self-healing propagation invariant optical fields.

Fracture detection by grating moiré and in-plane ESPI techniques

Abstract Optical interferometry techniques have been used for high-precision displacement measuring. Commonly, in-plane sensitive arrangements use two symmetrical collimated wavefronts for object surface illumination. However, this is a limitation when large object surface, has to be analyzed. In this case spherical illumination is needed. As a consequence of using non-collimated symmetrical dual-beams the sensitivity vector varies with the local position on the surface target. Then, this kind of illumination is also capable of detecting a lightly and systematic out-of-plane component of deformation. In this paper a theoretical analysis of the sensitivity vector components behavior is made. Each component of the sensitivity vector to minimize the required displacement component uncertainty is calculated. This study is important in the stage of planning any interferometric measurement experiment, particularly, for moire grating interferometric technique, which has been used only in collimated illumination. By using a spherical dual-beam optical setup, the present work shows results of fracture measuring by using moire and speckle interferometric methods. As a result, advantages and disadvantages of both techniques are discussed and an accuracy study is reported.

Measuring displacement derivatives by electronic speckle pattern shearing interferometry (ESPSI)

Electronic speckle pattern shearing interferometry (ESPSI), also known as shearography, is a whole-field optical technique used to measure approximately the fields of displacement derivatives. The accurate measurements of these derivatives have two problems: first, although ESPSI results are approximately equal to the derivatives, they are equal to the derivatives only if the shear distance tends to zero, hence, if experimental data rendered by ESPSI are taken directly as equal to the derivatives, the measurements may carry an important shearing error; second, ESPSI yields values relative to a reference value at a specific location of the field that can be very difficult to determine accurately. In this paper, we propose a general procedure to compensate the shearing error and to introduce the reference by adding two quantities to the values rendered by ESPSI. As an example, we measured a displacement derivative field induced on a metallic sheet specimen by applying tensile load.

Experimental demonstration of a Raman effect–based optical transistor

We demonstrate optical pulse switching and amplification based on simultaneous Raman and Kerr effects in a fiber-loop mirror. Stimulated Raman scattering is shown to play a dominant role in the transfer function of the loop with highly germania-doped fibers, in agreement with theoretical predictions. Optical switching of a 100-ps signal pulse with an amplification factor of 10 was demonstrated in a 20-mol.% GeO(2)-doped fiber.

Correction masks for thickness uniformity in large-area thin films

Experimental results from the emission of vapor sources are considered in designing correcting diaphragms to achieve a uniform thickness distribution during evaporation of thin films mounted on large-area substrate holders, in different geometric configurations.

General model to predict and correct errors in phase map interpretation and measurement for out-of-plane ESPI interferometers

Out-of-plane configurations used in electronic speckle pattern interferometry (ESPI), introduce phase error interpretation in extended target objects due to spatial variation of the sensitivity vector. In this paper, a general model to predict and correct the displacement measurement error and error phase map interpretation taking into account the target shape, illumination geometry, and in-plane displacement information, is presented. This model generalizes and extends previous analyses with respect to the sensitivity vector variations. The model is based on a relationship between variable sensitivity vector and the constant one. The importance of illumination geometry and in-plane displacement as factors that introduce the biggest error in the interpretation of the phase map are stressed. An analysis with practical parameters using divergent and collimated beams is presented. In order to predict and correct the error of phase interpretation, the finite element method should be used to obtain in-plane proportional factors to build up the correction function. The analysis shows that the error can be large for common configurations even when using collimated beam. To compute the measurement directly from the phase map, a general sensitivity function taking into account the shape and in-plane displacement information is naturally obtained from the presented analysis.

Error in the measurement due to the divergence of the object illumination wavefront for in-plane interferometers

Commonly, in-plane sensitive interferometric optical arrangements use two symmetrical collimated wavefronts for object surface illumination. However, this is a limitation when large objects have to be analyzed. In this case spherical illumination is needed. Non-collimated symmetrical dual-beam techniques have been performed. This kind of illumination produces a sensitivity vector varying with the position. Then errors in the measurements are introduced when collimated illumination is supposed especially in extended target objects. In the present work, an in-plane configuration for electronic speckle pattern interferometer (ESPI) is used. During the design stage of an interferometer should be useful to know the components of sensitivity vector in order to minimize the un-required displacement components. This is main task of this paper. We present theoretical analysis and experimental results for object divergent and collimated illumination. The errors are obtained by comparing the in-plane displacement calculated supposing constant sensitivity vector and spatial variation of sensitivity vector for object divergent illumination. This analysis is made for a flat and cylindrical object surface target.

Enhanced backscattering from a one-dimensional rough dielectric film on a glass substrate

We have observed the enhanced backscattering of light from a characterized dielectric film deposited upon a glass substrate when the light illuminates the rough surface from the vacuum. The vacuum-dielectric interface is one dimensional, randomly rough, while the dielectric-glass interface is approximately planar. Numerical and experimental studies reveal that the main mechanism responsible for the enhanced backscattering is the constructive interference between two waves that follow reciprocal scattering paths through the dielectric film, which is also strengthened by the multiple scattering from the rough vacuum-dielectric interface.

Coherence in the single and multiple scattering of light from randomly rough surfaces.

One of the most interesting phenomena associated with the scattering of light from a randomly rough surface is that of enhanced backscattering. This is the presence of a well-defined peak in the retroreflection direction in the angular distribution of an incoherent component of mean scattered intensity of the light scattered from such a surface that is primarily due to the coherent interference of each multiply reflected optical path with its time-reversed partner. It is an example of a broader class of multiple-scattering phenomena that goes under the name of weak localization. Not all manifestations of weak localization in the interaction of light with a randomly rough surface are in backscattering. It was recently shown that the average diffuse intensity from randomly rough surfaces with even symmetry can be enhanced or reduced in the specular direction because of the constructive interference between correlated pairs of scatters. We present a recent theoretical analysis and experimental results that cover four kinds of enhancement: enhanced backscattering, enhanced transmission, enhanced specular, and enhanced refraction for one-dimensional and two-dimensional surfaces. These are manifestations of coherent effects that remain after ensemble averaging.