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Incoherent optical information processing is known to be far less sensitive to noise than coherent processing. However, it is restricted to real non-negative quantities. In cases like approximate deconvolution for image restoration, where positive and negative quantities are involved, the use of incoherent illumination is possible only at the expense of some additional sophistication needed to incorporate the negative parts; in particular, the restoration can be achieved by combining two incoherent convolutions and one subtraction. This paper describes an experiment of this type, with special emphasis on the practical implementation and on the difficulties related to the subtraction. Alignment and normalization of the two images to be subtracted are critical issues. If the subtraction is performed optically, the dynamic range of this operation is an additional problem.

The visualization of traveling acoustic waves is achieved by means of acoustic stroboscopy. The limitations of the technique, interpretation of results, frequency range, and optical noise are reviewed. Two methods of noise reduction are studied: spatial filtering and holography. Optical holography of acoustic fields is also shown to offer the best advantages among the various methods of visualization outlined here.

In this paper, gamma ray imaging using Fresnel zone plates is studied. We show that an M.T.F. can be associated with the coding—decoding process giving an evaluation of the final image quality. An experimental result corroborates the theoretical study.

We present here a 3-D image processing applied to coded aperture imaging. As a code we use a ring, and decoding is performed by deconvolution. Depth and lateral resolution are examined by Fourier and object space analyses. In particular contrast inversions are put in evidence and their influence in nuclear medicine is discussed. The theory is confirmed first by computer simulations, then by “in vivo” images of the heart.

We show the possibility and the conditions of the filtering of in-line holograms in aspheric testing. A general comparison of in-line and carrier frequency holograms applied to aspheric testing is also given.

On determine, en eclairage coherent, les relations generales de correspondance objet-image dans un systeme optique. Ces relations ne presentent pas habituellement le caractere d'invariance avec les translations, ou selon la terminologie usuelle (impropre), elles sont non lineaires. On montre qu'il est possible de realiser la linearite dans un champ etendu, aussi bien en intensite qu'en amplitude.

Strictly speaking, a moving diffuser illuminated by laser light is equivalent under certain conditions, to an incoherent light source only when the observation time is infinite. When the observation time T is finite, a residual speckling appears. The corresponding signal to noise ratio in the observed illuminance is calculated for uniforn or non uniform diffuses in two cases of interest: 1. 1)Observation in the image plane of an optical system. 2. 2)Observation in the Fresnel field of the moving diffuser. The signal to noise ratio is expressed as a simple function of the diffuser's displacement and of the impulse response of the system.

The image of an object illuminated with laser light through a moving diffuser is not always the same as that obtained with a thermal source. The experimental conditions necessary for equivalence are determined. Even when these conditions are not fulfilled, the mutual intensity in the image is related in a simple way to the autocorrelation of the diffuser.

Noise problems in image processing by optical filtering are examined. A comparison between coherent and incoherent illumination is made.

Several X-ray and XUV diagnostic techniques have been stimulated by research on high density plasmas produced in laser fusion, by X-ray laser studies, astrophysics and by studies using synchrotron generated X-rays. Most of these techniques can be crudely divided in two classes : The first class includes in particular time resolved spectroscopy and one dimensional (1D) space-time imaging. A comprehensive description of several time resolved devices can be found in Ref. 1. The se-cond class includes purely space resolved imaging systems. This paper in no way attempts to review all progress in X-ray diagnostics. However since most of the diagnostic devices use some imaging system, generally of microscope type, we shall review the principal two-dimensional (2D) or three-dimensional imaging systems with emphasis on the relative image properties and on the progress introduced by the advent of X-ray multilayers.

Tri-dimensional imaging of X-rays emitted by laser induced plasmas can be performed by Coded Aperture Imaging (C.A.I.) using a "multislit11 code and linear CCD detectors in order to provide real-time imaging. We present the realization of this Multislit CCD camera.1. INTRODUCTION : Coded Aperture ImagingMicroimaging of X-rays emitted by laser induced plasmas provides useful informations on plasmas characteristics. Time resolution as well as spatial resolution are of great interest. Our study is limited to three- dimensional (3D) spatial resolution. C.A.I, appears to be well suited for that, because of its high luminosity and tomographic capa­ bility in a static device recording.C.A.I, belongs to imaging methods by co­ ding and reconstruction, operating in two steps :1) Recording of the emitting distribution by geometrical shadowcasting through a coding mask, the detector being parallel to this code (fig. 1) : in fact, it is similar to the well known pinhole camera, the pinhole being replaced by a more complicated mask, for instance Fresnel zone plate, annulus, array of pinholes,L ' 2 .2) Reconstruction, or decoding, is next re­ quired to recover a recognizable image of the source. This decoding is usually perfor­ med digitally and must match the chosen co­ de. But general C.A.I, reconstruction con­ sists in a two-dimensional deconvolution, leading to a considerable computation load.That is why we developed a new type of coding, derived from Medical Imaging, which permits a decoding calculation easier to perform, since mostly one-dimensional, be­ cause of its peculiar configuration : the code is composed of a large number of narrow slits at various angles in a unique plane.In next section, we examine this "multi- slit" coding, associated with a simple re­ construction by blurring, and we show expe­ rimental results. In section 3, we present the realization of a multislit camera using CCD detectors in order to perform direct acquisition and thus real-time imaging. Fi­ nally, in section 4, we develop a more accu­ rate reconstruction by considering the whole 3-D problem and adding a priori informations when available. We will conclude this paper by the project of using simultaneously two such coding cameras in two different direc

A simple method for measuring phase velocities of vibration modes in a bar is described. Experimental results for aluminum are compared with values computed from theoretical curves of the phase velocity versus frequency thickness product.

Under coherent illumination, the interference between signal and noise produces an amplification of the noise. That is why image processing by optical methods may be done better with incoherent light than with coherent light. A method is described where image deblurring is performed in spatially incoherent illumination. The two main features are an additional step of illuminance subtraction to simulate negative intensities, and the use of computer-generated holograms of a low number of cells.

Fluctuations in image illuminance resulting from various sources of optical noise are studied as a function of the spatial coherence of the illumination. It is shown that noise fluctuations caused by the pupil plane can be reduced considerably by using incoherent, or even partially coherent, rather than coherent illumination. Conversely, noise caused by defects in the object plane is not affected by the degree of coherence, except for phase noise which is suppressed in incoherent light. Expressions for noise fluctuations are developed on the basis of a simplifying Gaussian assumption for the noise sources; the validity of this assumption is justified.

The two basic optical Fourier transform configurations are examined with respect to component complexity, aberrations, and optical noise. It is shown that the converging-beam illumination setup (CB-FT) is much simpler and works better than the classical parallel beam illumination setup within a restricted range of object size and lens aperture. This range corresponds to many practical cases. Therefore, the CB-FT should be preferred in ordinary cases whereas the classical setup with a special purpose Fourier lens should be used only for a large space-bandwidth product. It is probably never a good solution to use the parallel beam configuration with a general purpose lens as the Fourier lens.

The observed density of a photographic record is dependent on the aperture of the illuminating and imaging optics. This effect, due to the scattering by the photographic emulsion, is analyzed using as few assumptions as possible. The results show a reasonable agreement with experiments on Callier effect found in the literature. In the realm of a study about noise and coherence in image processing, the influence of the Calier effect on image contrast is discussed. It is found in particular that contrast variations may be large (over a factor of 10 in some cases) and that the best contrast is obtained for a certin partially coherent illumination.

Optical Fourier analysis of acoustic fields is used for the interpretation of acoustic disturbances. The method is applied to the study of modes propagating in an elastic waveguide. In particular, the mode dispersion curves are determined with an accuracy greater than that with purely acoustic methods.

A new method is presented allowing study in real time of the intensity pattern of diffusing sources. The classical method of point by point plotting of scattered light intensity is replaced by the measurements of some coefficients, called "moments", directly containing all the desired information. This method uses an integrating sphere with a non-uniform coating. The principle of the method is explained, and then some experimental results proving its feasibility are presented. Finally we describe further improvements allowing actual application to the determination of the size and the shape of macro-molecules in a liquid solution.

The properties of the amplitude and illuminance of the images of coherently illuminated diffuse objects are studied. Uniform and nonuniform objects are considered. The image illuminance is considered to result from a linear transformation of a nonstationary gaussian stochastic process followed by a square-law detection. Expressions are obtained for the mean, autocorrelation, variance, and spatial power spectral density of the amplitude and of the illuminance. Interpretation of the results led to conclusions concerning the speckle size, the noise power in the image, and the transfer function of an optical system when the object diffuses coherent light. When the autocorrelation width of the random fluctuations of the object amplitude is small compared to the impulse response of the system, the mean illuminance in the image plane is that which would be given by an incoherent object having the same luminance as the object considered; the average speckle size is equal to that of the impulse response of the system; the average transfer function of the system is the incoherent transfer function; and the distribution of the noise spatial frequencies does not depend upon the form of the signal, but only upon its total energy. Other results concerning the image statistics have also been obtained.

A moving diffuser destroys the spatial coherence of laser light only partially when the integration time is finite; this can be expressed by the signal-to-noise (S/N) ratio in the observed illuminance, due to the residual speckle. The method can be improved by the use of a two-diffuser system of which one diffuser is motionless, the other moving. In this case, the integration time (or the displacement of the diffuser) required to obtain a given S/N ratio can be greatly reduced, allowing the use of a slowly moving diffuser. Moreover, the S/N ratio does not depend on the optical-system parameters, whereas it depends on these parameters when a single diffuser is used.

A general solution for the radiance distribution inside a sphere is developed for nonuniform, nonlambertian diffusely scattering surfaces. This provides a method for investigating the surface scattering transfer characteristics or the initial irradiance distribution. It is demonstrated that the surface structure and reflectance variations affect the classical radiant flux photometric measurement. Using specific reflectance patterns, it is possible to measure specific spherical harmonic moments of the initial irradiance distribution.

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Développement de diagnostics expérimentaux permettant d'étudier les masses éjectées obtenues a partir de défauts de surface reparties ou localises. Evaluation de la masse éjectée en fonction de la vitesse des particules moyennant l'hypothèse du transfert inélastique de la quantité de mouvement entre l'éjecta et une cible mince placée initialement devant la surface libre et dont on suit la vitesse par interférométrie doppler laser. Etude de la structure spatiale des éjecta au moyen d'un générateur de rayons-x pulse et de l'évolution des contours a l'aide d'une camera ultrarapide a images intégrales. Elaboration d'un modèle.