S. Lowenthal's research while affiliated with French National Centre for Scientific Research and other places

Publications (51)

Conference Paper
Tri-dimensional imaging of X-rays emitted by laser induced plasmas can be performed by Coded Aperture Imaging (C.A.I.) using a "multislit" code and linear CCD detectors in order to provide real-time imaging. We present the realization of this Multislit CCD camera.
Chapter
Reporting the first x-ray holography experiment performed in Europe, we should acknowledge previous works in the field [1–4]: their results make it no longer necessary to demonstrate that x-ray holography can be achieved with available means. However, in our opinion, there is presently no evidence that this method can become a practical, routine te...
Chapter
In X-ray contact microscopy, the image detector is usually a photoresist which is observed, after development, with an electron microscope. With this simple technique very high resolutions have been demonstrated, but quantitative measurements are very difficult to obtain [1,2]. Quantitative and real-time images can be produced on a high resolution...
Article
X ray to visible conversion is performed in an array of scintillating optical fibers designed for contact imaging with synchrotron radiation. The advantages of the device in terms of spatial resolution and detection quantum efficiency for high-flux imaging over 5 keV are discussed. We present experimental results with a scintillating liquid core fi...
Article
X-ray microscopy with synchrotron radiation is a way of obtaining, on biological objects, informations which can be different of what is seen with usual microscopes and microanalysers. Living specimens can be observed and x-ray absorption analysis can be performed by scanning the wavelength during observation. Contact imaging with a photoelectronic...
Article
In the soft x-ray region, different techniques have been recently developed which can give images of biological objects at an intermediate resolution between optical and electron microscopes. At these wavelengths, very little sample preparation is required because the image contrast is directly dependent upon the chemical composition of the sample...
Article
Les rayons X mous, dans une bande qui s'étend entre 1 et 10 nm de longueur d'onde, présentent un intérêt majeur en microscopie X. Pour l'exploiter il faut cependant disposer d'un instrument résolvant et capable de travailler à longueur d'onde variable. Nous décrivons ici un microscope X à conversion d'image basé sur l'émission électronique secondai...
Chapter
Using absorption edges for contrast enhancement or microchemical analysis has been often claimed as one of the main advantages of the soft x-ray microscopy; the K edges of carbon to aluminium and L23 edges of phosphorus to bromine are located in the 0, 8–9 nm wavelength range which is very favourable to image biological objects. But in practice, th...
Article
A photoelectron X-ray microscope is described which is based on the principles of contact X-ray imaging and of image converters. An X-ray image is projected by a parallel X-ray beam on a thin transmission photocathode. The emitted electrons are accelerated and imaged at large magnification by an emission microscope.The instrument, which is presentl...
Article
Synchrotron radiation is used for X-ray microscopy and microanalysis. The contact imaging method in conjunction with absorption spectroscopy near an absorption edge offers the advantages of high spatial resulution and large field mapping of atomic species in the whole X-ray spectrum. Quantitative analytical charts are obtained from images recorded...
Article
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. Thi...
Article
X-ray absorption microanalysis by contact microscopy with synchrotron radiation potentially offers the advantages of high resolution and large fields. However, difficulties appear when quantitative results are required, due in particular to the image detectors that are used. The degree of confidence in quantitative results is examined for photograp...
Article
Les examens de tomographie axiale transverse souffrent de limitations statistiques. A partir des processus de Poisson unidimensionnels que constituent les projections, nous analysons les éléments de dépendance du rapport signal sur bruit, aussi bien en tomographie d'émission qu'en tomographie d'absorption. Ensuite, dans le cadre de la tomographie d...
Article
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 expen...
Article
Synchrotron radiation has recently contributed to the development of high‐resolution x‐ray microscopy either for biological investigations or for chemical microanalysis. Contact microscopy for this end appears to be particularly useful, but is mainly limited by the detectors that are used. In order to overcome these limitations—i.e., to obtain real...
Article
Optical image formation (and processing) is strongly affected by film grain noise. The noise effects depend on the spatial coherence of the illumination. In this paper we shall analyze these phenomena in the case of Kohler illumination. The effective transmittance of any photographic image is instrument dependent due to diffusion by the grain (Call...
Article
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.
Conference Paper
Optical image formation (and processing) is strongly affected by film grain noise. The noise effects depend on the spatial coherence of the illumination. In this paper we shall analyse these phenomena in the case of Kehler illumination. The effective transmittance of any photographic image is instrument dependant due to diffusion by the grain (Call...
Article
The invention provides a holographic device for X-ray or gamma ray imaging, especially for tomography in the medical field, in which low frequencies of radiation can be included in the image construction by virtue of having a mask with a particular transmittance law. For example the transmittance law of the mask may be such that transmittance is a...
Article
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 caus...
Article
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 confi...
Article
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 st...
Article
The use of synchrotron radiation is shown to give promising properties to x‐ray absorption microanalysis. Geological samples, 30 μm thick, have been analyzed over large areas with a few micrometers resolution, and maps of transition‐metal distributions were obtained in less than 15 min. An increased resolution is expected with x‐ray resists.
Article
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 ad...
Article
The proposed method is an image deblurring technique performed under incoherent illumination. This is to avoid the well known coherent noise which often limits the quality obtained by using optical coherent processors. Synthetic holograms with a small number of cells are used in an intermediate step of the elaboration of two natural holographic fil...
Article
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.
Article
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.
Article
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...
Article
Computer generated holograms improved significantly the possibilities of optical data processing by spatial filtering. Nevertheless, a practical limitation appears when the processed image has to contain a large number of degrees of freedom, i.e., when a large space bandwidth product is involved. The aim is to elude this difficulty and to compute a...
Article
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.
Article
Citation J. Braat and S. Lowenthal, "Short-exposure spatially incoherent holography with a plane-wave illumination," J. Opt. Soc. Am. 63, 388-390 (1973) http://www.opticsinfobase.org/josa/abstract.cfm?URI=josa-63-3-388
Article
The amplitude and phase distributions of a progressive acoustic wave are visualized simultaneously by means of acoustic stroboscopy. Two methods are described: (i) modulation of a laser beam by a progressive acoustic wave; (ii) modulation by a stationary wave. Spatial filtering of diffracted orders enables the progressive wavefronts to be seen as i...
Article
A method using a birefringent prism to subtract illuminance (intensity) is described. It is shown that the subtraction can be performed either with spatially coherent or incoherent light, the noise being greatly reduced in the latter case.
Article
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 th...
Article
Citation S. Lowenthal and J. Braat, "Subtraction of Intensities by Means of Spatially Incoherent Fourier Holography," Appl. Opt. 10, 2553-2554 (1971) http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-10-11-2553
Article
Small transverse (in plane) displacements or vibrations are measured in real time. The range goes from Angströms to a few microns. The method only needs coherent illumination of the surface under examination.
Article
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. I...
Article
Citation Y. Belvaux and S. Lowenthal, "White Light Hilbert Transform," Appl. Opt. 10, 676-677 (1971) http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-10-3-676
Article
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...
Article
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 un...
Article
Fourier transform holograms of transilluminated objects are considered. It is shown that for a fixed recording configuration, both a given number of resolution cells and a given signal to noise ratio can be obtained in the reconstructed image. This is applicable to both coherent and incoherent holograms.
Article
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 di...
Article
Citation S. LOWENTHAL, J. SERRES, and C. FROEHLY, "Double-Exposure Interferometry by Spatially Incoherent Recorded Holography," J. Opt. Soc. Am. 60, 421-422 (1970) http://www.opticsinfobase.org/josa/abstract.cfm?URI=josa-60-3-421
Article
A method for observing phase objects, based on the Hilbert transform is defined. This is achieved by spatial filtering. The amplitude images obtained are characterized by their high luminosity. The objects are correctly imaged, even if the phase varies slowly (low frequency objects), which is not the case with conventional methods such as the phase...

Citations

... Thus, when the prospect of x-ray laser and synchrotron radiation sources with many orders of magnitude more coherent power appeared in the early 1980's, interest in x-ray holography revived. 6,7 Experimental programs were started at various centers, [8][9][10] using mostly undulator x-ray sources and polymer photoresist detectors, and these led to the achievement of submicronresolution reconstructed images at Brookhaven 11,12 and Orsay 13 and the demonstration of x-ray laser holography at Livermore. 14 High-resolution x-ray Fourier holography was also demonstrated for the first time by McNulty et al., 15,16 and the history of all these efforts was reviewed by Jacobsen. ...
... In Fourier optics the concept of a derivative operation plays an important role for describing the propagation in free space [l-31 and the influence of wave aberrations [4], for visualizing phase structures [5, 61, and in general for edge enhancement [7], image deblurring [8], and pattern recognition [9]. ...
... Coded Aperture Imaging is a simple technique for investigating reconstruction of two or three dimensional sources that was introduced in the 70's. It continues to interest several fields, especially optics ( [3], [5], [7], [11], [12], [21], [25]), nuclear medicine ( [2], [6], [13], [14], [23], [24]), and astronomy ( [1], [16], [17], [18], [20]). Coded Aperture Imaging reconstruction in the two dimensional case has led to good results because it is equivalent to the classical deconvolution problem. ...
... Lots of methods have been developed that are dedicated to different ranges of applications and based on different physical phenomena. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] The work reported in the proceeding is concerned with the use of a low cost vision system as a tool for in-plane vibrations. A stroboscopic illumination allows a frequency shift of the inspected vibration toward the bandwidth of a standard CCD camera. ...
... The basic physics behind these techniques is to modulate the images by interference fringes instead of using a mechanical grating. Belvaux and Lowenthal [4] used the fringes produced by Wollaston prism placed between two suitable polarizers. The fringe pattern so obtained can be shifted by half-period just by rotating the polarizer at the output by 90 • . ...
... Speckle noise typically occurs in coherent imaging systems such as lasers, acoustics, synthetic aperture radar (SAR) and medical ultrasound imaging. Speckle noise is an unwanted consequence of the image formation process in coherent imaging [1][2][3][4][5]; the speckles mask details and thereby complicate image analysis. ...
... 23) However, this leads to unwanted coherence artefacts, i.e. speckles, which inevitably deteriorate the image quality. [24][25][26][27] Partially coherent or incoherent illumination has demonstrated the ability to suppress the speckles in SPC imaging as well as other imaging modalities. [28][29][30] However, reducing coherence degree also degrades the image quality due to unwanted blur and loss of contrast. ...
... To circumvent this limitation, we propose a new method based on extending the opto-electronic theory of two-pupil synthesis [Chavel and Lowenthal 1976;Lohmann and Rhodes 1977] to metasurfaces. ...
... Although debated [126], this result has been confirmed (and extended) numerically by McEwen et al. [127]. Further studies [128][129][130][131][132] show that for fixed SNR, increasing the spatial resolution requires to increase the dose [see also 104, §4.4.5]. ...
... We have designed an optical test system that had two illumination lenses and a test plate with a CGH fabricated onto a spherical reference surface. The curved CGH in our system is fabricated by using a new technology that combines laser direct writing and lithography [11][12][13][14]. The particular characteristics of this new type of CGH could derive higher accuracy, efficiency and lower cost for testing aspherics in comparison to other CGH employed previously by other authors. ...