Multiple passages of light through an absorption inhomogeneity in optical imaging of turbid media

The multiple passages of light through an absorption inhomogeneity of finite size deep within a turbid medium is analyzed for optical imaging using the ``self-energy'' diagram. The nonlinear correction becomes more important for an inhomogeneity of a larger size and with greater contrast in absorption with respect to the host background. The nonlinear correction factor agrees well with that from Monte Carlo simulations for CW light. The correction is about $50$ in near infrared for an absorption inhomogeneity with the typical optical properties found in tissues and of size of five times the transport mean free path.Comment: 3 figure

Synchrotron radiation representation in phase space

The notion of brightness is efficiently conveyed in geometric optics as density of rays in phase space. Wigner has introduced his famous distribution in quantum mechanics as a quasi-probability density of a quantum system in phase space. Naturally, the same formalism can be used to represent light including all the wave phenomena. It provides a natural framework for radiation propagation and optics matching by transferring the familiar `baggage' of accelerator physics (beta-function, emittance, phase space transforms, etc.) to synchrotron radiation. This paper details many of the properties of the Wigner distribution and provides examples of how its use enables physically insightful description of partially coherent synchrotron radiation in phase space

Image reconstruction techniques; (170.3880) Medical and biological imaging

Abstract: Diffuse optical tomography (DOT) reconstructs the images of internal optical parameter distribution using noninvasive boundary measurements. The image reconstruction procedure is known to be an ill-posed problem. In order to solve such a problem, a regularization technique is needed to constrain the solution space. In this study, a projection-error-based adaptive regularization (PAR) technique is proposed to improve the reconstructed image quality. Simulations are performed using a diffusion approximation model and the simulated results demonstrate that the PAR technique can improve reconstruction precision of object more effectively. The method is demonstrated to have low sensitivity to noise at various noise levels. Moreover, with the PAR method, the detectability of an object located both at the center and near the peripheral regions has been increased largely

Wigner distribution in optics

In 1932 Wigner introduced a distribution function in mechanics that permitted a description of mechanical phenomena in a phase space. Such a Wigner distribution was introduced in optics by Dolin and Walther in the sixties, to relate partial coherence to radiometry. A few years later, the Wigner distribution was introduced in optics again (especially in the area of Fourier optics), and since then, a great number of applications of the Wigner distribution have been reported. While the mechanical phase space is connected to classical mechanics, where the movement of particles is studied, the phase space in optics is connected to geometrical optics, where the propagation of optical rays is considered. And where the position and momentum of a particle are the two important quantities in mechanics, in optics we are interested in the position and the direction of an optical ray. We will see that the Wigner distribution represents an optical field in terms of a ray picture, and that this representation is independent of whether the light is partially coherent or completely coherent. We will observe that a Wigner distribution description is in particular useful when the optical signals and systems can be described by quadratic-phase functions, i.e., when we are in the realm of first-order optics: spherical waves, thin lenses, sections of free space in the paraxial approximation, etc. Although formulated in Fourier-optical terms, the Wigner distribution will form a link to such diverse fields as geometrical optics, ray optics, matrix optics, and radiometry. Sections 1.2 through 1.7 will mainly deal with optical signals and systems. We treat the description of completely coherent and partially coherent light fields in Section 1.2. The Wigner distribution is introduced in Section 1.3 and elucidated with some optical examples. Properties of the Wigner distribution are considered in Section 1.4. In Section 1.5 we restrict ourselves to the one-dimensional case and observe the strong connection of the Wigner distribution to the fractional Fourier transformation and rotations in phase space. The propagation of the Wigner distribution through Luneburg’s first-order optical systems is the topic of Section 1.6, while the propagation of its moments is discussed in Section 1.7. The final Section 1.8 is devoted to the broad class of bilinear signal representations, known as the Cohen class, of which the Wigner distribution is an important representative

Instabilities in the piezoelectric properties of ferroelectric ceramics

The large piezoelectric effect of ferroelectric ceramics is utilized in many devices for sensing and actuating purposes. In this paper, the longitudinal direct piezoelectric effect in ceramics based on lead zirconate titanate, lead titanate, barium titanate and bismuth titanate is investigated as a function of the amplitude and frequency of the external pressure, the crystal structure and microstructure of the ceramics. The domain-wall contribution to the piezoelectric response appears to be a dominant extrinsic origin of instabilities in the observed piezoelectric effect but, for a given composition, it can be affected by dopants and microstructure. Other sources of instabilities in the piezoelectric response, such as chemical inhomogeneities and defects, are also discussed. It is shown that, with proper modifications, it is possible to freeze out completely the extrinsic part of the piezoelectric response in some of the examined compositions and to obtain a stable behaviour, independent of the frequency and magnitude of the external driving held

Microstructure, electrical conductivity, and piezoelectric properties of bismuth titanate

A study was conducted on the effects of microstructure, atmosphere, and several dopants on the electrical conductivity of bismuth titanate (Bi4Ti3O12, BIT), Increased grain size increased the conductivity in undoped BIT as did acceptor dopants that substituted for either Bi (Ca and Sr) or Ti (Fe), A donor dopant (Nb) decreased the conductivity in BIT by as much as 3 orders of magnitude, The increased resistivity of Nb-doped BIT improved the polarization in an electric field, A piezoelectric coefficient, d(33), of 20.0 pC/N was achieved with a Nb-doped BIT composition corresponding to Bi4Ti2.86Nb0.14O12

Herstellung 3D-integrierter optischer Verbindungsmodule in Diffusionstechnik und LIGA Abschlussbericht

The goal of the project was the development of a technique which allows to integrate optical free space interconnections in a miniaturized form. By this three-dimensional integration optical systems can be realized in a more compact form. Thus integration densities could be achieved, which are comparable to micro-electronics. The basic elements of this integration technique are the use of a stacked-layer technique, lithography and refractive optics. For numerical simulation of the light propagation through refractive components a new method, the wave-propagation method (WPM) was developed. Compared to paraxial approximations this method allows the treatment of propagation angles up to 70 degrees. For this project three technologies have been employed: micro lenses were fabricated by ion exchange in glas. Beam splitting and beam deflecting elements were fabricated with LIGA-technique and beam forming elements have been realized by photo-polymerisation. By combining the individual component arrays a micro-optical system was demonstrated, which performs a perfect-shuffle permutation on an arry of 100 data channels within a volume of less than one mm"3. (orig.)SIGLEAvailable from TIB Hannover: D.Dt.F.QN1(14,2) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman