Publisher Summary This chapter focuses fringe formations in deformation and vibration measurements using laser light. The chapter discusses a survey on the formation of the fringe patterns observed in these methods. The chapter helps in deriving dependences of their shape and visibility on object deformation parameters and optical systems by starting from the correlation properties of the light scattered from diffuse objects, and discuss the mutual relationships and features of each method by putting physical interpretations on derived mathematical relations. In holographic interferometry and speckle interferometry, the fringe shape represents the distribution of the phase change of the scattered light caused by object deformation, while the fringe visibility depends on the overlap of the corresponding speckle pair, therefore, on speckle displacement and speckle size. In speckle photography, on the other hand, the fringe shape represents the speckle displacement, while the fringe visibility is affected by the speckle decorrelation accompanying the displacement. In addition the relations derived in the present chapter would deliver a quantitative basis for selecting an adequate method of measurement and the optimum manner of signal processing in these modem interferometric techniques.

V Fringe Formations in Deformation and Vibration Measurements Using Laser Light

Holographic interferometry is a very powerful technique for the measurement of small deformations and displacements of opaque solid objects. Unfortunately, the quantitative interpretation of the fringe patterns is somewhat involved, and the large number of papers published on this subject in the past 10 years has caused considerable confusion. This review paper is an attempt to rationalize the field by classifying the many different interpretation schemes into four main techniques, and by offering guidelines for the choice of technique for different applications.

The interpretation of holographic interferograms

Utilisation des franges d'interference en lumiere diffuse pour l'etude de l'etat de surface d'un diffuseur

The interpretation of the fringe pattern formed by a double-exposed hologram of a deformed object leads first to the displacement of a point of the object surface. Further, if one desires to know the strains and the rotations at this point without numerical differentiation, the concept of the line of complete localization may be used. Associated to each point of the surface there is a locus in space where the light waves reflected by the vicinity of this point have all the same phase shift. Points of this curve may be determined by a criterion concerning the direction of the fringes and by use of a special device based upon it. Linear equations yield then directly and in general cases the sought strains and rotations. Some experimental results are given which attempt to show the applicability of this method. Further developments should permit the investigation of the constitutive equation of any non-transparent body.

On direct measurements of strain and rotation in holographic interferometry using the line of complete localization

Up to now, we have investigated, on the one hand, the kinematics of the deformation of a body (Sect. 2.2) and, on the other hand, the formation of holographic images (Chap. 3). In this chapter, these two subjects will be combined, because we are going to explain how holography can be used to measure deformations.

Chapter 4 Fringe Interpretation in Holographic Interferometry

For the case of holographic interferometry when one measures changes in position and shape of diffusely reflecting surfaces new, quite general relations determining the localization of interference fringes are derived. The important properties of fringe localization are also discussed and a useful practical solution is drawn.

I. Přikryl

Papers

Localization of Interference Fringes in Holographic Interferometry