Deformation of the modulation profile in phase holographic gratings.

Among all the parameters that characterize a phase grating, the most difficult to control is the modulation profile of the refractive index. In fact, it covers many scalar parameters that are the Fourier coefficients of the profile. To study the influence of processing baths on the modulation profile, in phase holographic gratings made of dichromated gelatin, we have observed that the shape of the profiles obtained sometimes presents a slight concavity or a convexity in the middle, leading to an increase or a decrease in the diffraction efficiency. We present the experimental results and a numerical study in the form of a theoretical prediction, which confirms the experimental observations.

Theory of moiré sensing by means of contour functions.

We present a mathematical analysis of moiré sensing in which the basic theoretical concept-and tool-is the concept of the contour function. We show that the mathematical analysis is simplified greatly by systematic recourse to this tool. The analysis that is presented permits a simultaneous treatment of two different modes of implementing the moiré technique: the direct mode (widely used and well known) and the converse mode (scarcely used). The converse mode consists of computing and designing a grating especially for one model of an object in such a way that if (and only if) the object is in conformity with theprescribed model, will the resulting moiré fringes be parallel straight lines. We give explicit formulas and algorithms for such computations.

Thickness measurement for volume holograms by analysis of first-order diffraction.

We present a method for measuring the thickness of volume holograms by analyzing the variations of the diffraction efficiency as a function of angle of incidence. This method can be justified theoretically within the Born approximation for gratings with small modulation. But we prove experimentally that the method can work surprisingly well even for strongly modulated volume holograms. The principle of the method consists of the determination of angles of incidence for which the first-order diffraction efficiency takes its extreme (maxima and minima) values: these angles are related to the thickness of the grating.

[Use of structured lights in the evaluation of thoracic deformity bound with cardiac activity. Study of apical impulse using Moiré technics]. / Utilisation des lumières structurées dans l'évaluation de la déformation thoracique liée à l'activité cardiaque. Etude de l'impulsion apicale à l'aide des techniques du Moiré.

Chest deformation due to cardiac activity can be studied with the use of techniques based on Moiré principle. The shadow technique allows to obtain well contrasted fringes, whereas the technique of projected Moiré allows an easier taking of camera pictures. The fringes in this case, although less contrasted, allow to recognize level differences of the order of 0.17 mm with a network of 20 traits/mm in the present configuration of our material. The best criteria of registration have been set up after the study of 10 young subjects. In the presented case topographic measurements allowed a quantitative evaluation of the apical impulse. The telesystolic image after treatment allowed a tridimensional reconstruction of chest deformation.

Evaluation of chest wall distortion related to cardiac activity by structured lights. A study of the apical impulse by the Moiré technique.

The use of structured lights and especially of the Moiré technique to evaluate chest wall distortion in front of the apical impulse allows a topographic study of the precordial movement in relation with cardiac activity. Shade Moiré technology offers the possibility to study a reduced area of the chest with a good enlargement effect and well contrasted fringes. Projected Moiré allows the study of an increased area of the chest (40 cm2) and provides less contrasted pictures with a reduced enlargement effect. Both techniques offer the possibility of automatic imaging. The study of a normal subject is realized with a topographic evaluation of the chest wall distortion on a endsystolic frame. 3D representation of the chest wall deformation is performed after image treatment on a endsystolic print.