Leopold Pflug

A Holographic Technique Featuring Broad Range Sensitivity to Contour Diffuse Objects

Abstract We have shown that the performances available from a two-source relief sensing interferometer are improved substantially by combining an innovative way of managing the phase resources inherent in the interferometer. The approach gives rise to the emergence of a flexible and versatile holographic contouring method capable of addressing surfaces of broadly varying depths. Experimental results are presented to support the proposal.

Holographic moiré phase reinforcement procedure to obtain variable sensitivity surface topographic mapping extension to phase stepping

Abstract This paper describes a holographic contour measurement technique based on a continuous reorganization of the phase data introduced in the interferometer. The possibility of applying the phase shifting technique to the method is briefly described. The most important feature of the method is that its sensitivity can be varied continuously and in real-time in a wide range.

Holographic interferometry at LSA: Some selected examples of its application

Abstract The Laboratory of Stress Analysis is involved in the research and development of optical techniques for deformation and shape measurements. The main consideration during this presentation will be to provide a brief description of some of the holographically related NDT applications carried out at our facility.

Mechanical testing of the external fixator by holographic interferometry.

Tests carried out on the Hoffmann- Vidal external fixator by means of holographic interferometry are reported. These tests refer exclusively to the quality of functioning of the joints connecting transfixing pins and side bars. It is a question of 1) evaluating the behavior of the ball joint subjected to realistic loads, 2) verifying the rigidity of a lightened joint bowl as compared to a heavier one, and 3) comparing the respective resistance of two similar joint models to a rotation of the bar around its axis. The main findings are the remarkable elastic behavior of the ball joint, the effectiveness of the lightened bowl, and the fact that two cousin models may behave quite differently with respect to their resistance to axial slipping rotation of the bar. The interferometric technique is thus expected to have further applications in similar evaluations.

Measurement of large out-of-plane displacements using two source holographic interferometry

Abstract A phase shifting holographic interferometry method is described that measures large out-of-plane deformations undergone by an object surface subjected to load. An experiment is carried out to demonstrate the measurement capability of the method.

Low coherence sensors for the monitoring of underground works.

Civil underground works offer good opportunities for fiber optic displacement sensors. This communication presents an overview of possible applications in this field. Low-coherence interferometry appears to be the ideal technique for the long-time monitoring of such structures. The principle of the portable measuring system developed at our institute and based on this technique is presented along with different possible multiplexing techniques. The presented experimental results confirm the precision of 10 micrometers found under laboratory conditions and the immunity to drift for at least one year. A description of the techniques used to install optical fibers in anchorage cables and piles, as well as the lessons learned from these field tests are also presented.

Real-time holographic phase organization technique to obtain customized contouring of diffuse surfaces

We report on the development of a holographic technique which allows one to obtain real time holographic fringes that reveal the whole field contour map of an arbitrary shaped object. The method enables one to generate sensitivities compatible with the relief variations of objects of broadly varying depths. This is achieved by supplying enough 3-D modulation capacity to the system to develop the desired sensitivity. The intersection planes can be pivoted to provide for an oblique slicing of the model. We describe the basic optical configuration and discuss the system parameters. Experimental results are presented to illustrate the effectiveness of the method.

A Fresh Approach of Phase Management to Obtain Customized Contouring of Diffuse Object Surfaces of Broadly Varying Depths Using Real-time Holographic Interferometry

Abstract A concept of phase management is introduced in holographic interferometry to obtain customized contouring of diffuse object surfaces. The proposal integrates several useful features: it is non-contact, whole-field, real-time and provides continuously variable sensitivity within a wide range. The method is experimentally shown to be effective for a broad range of object depths.

Novel concept for obtaining continuously variable topographic contour mapping using holographic interferometry

A holographic technique is developed which allows one to obtain in real time the contour map of an arbitrarily shaped object. The method provides a relatively coarse contouring of the object. While still operating at low sensitivities, the method suffers from a breakdown in its functioning due to a saturation of the phase carrying capacity of the interferometer. As a consequence, a phase management strategy is introduced, whose incorporation to the technique enables a substantial improvement of its performance. These developments are systematically analyzed and presented. The method is whole field and noncontacting. The live and flexible character of the method enables one to rapidly generate sensitivities tuned to the relief variations of objects of broadly varying depths. Experimental results are presented to illustrate the feasibility of the proposals.

Holographic Interferometry Applied At Subfreezing Temperatures: Study Of Damage In Concrete Exposed To Frost Action

The aim of this research is to use holographic interferometry to evaluate the frost susceptibility of concrete. Concrete specimens are subjected to subzero temperatures inside a freezing cabinet. A holographic system is implanted astride both the interior and exterior of the cabinet. Problems related to the implementation of such a measurement system are discussed, and ways to overcome them are described. A fringe control capability eliminates the influence of rigid-body movements and controls the fringe density. The developed system enables one to monitor in real time the evolution of the deformation of concrete specimens exposed to freezing cycles. Besides demonstrating the existence of stresses arising from the thermal incompatibility between the components of the concrete, the method provides an accurate measurement of the temperature at which this thermal incompatibility leads to the impairment of the hardened concrete paste. Results computed from the application of a mathematical model are compared with those obtained by holographic interferometry. Close agreement between the numerically computed and the experimentally observed behavior is obtained.