X-ray-Absorption Spectral Study of the R₂Fe₁₇₋ₓMₓ Solid Solutions (R=Ce, Nd and M=Al, Si)

The x-ray-absorption near-edge structure (XANES) spectra obtained at the cerium LIII edge of the Ce2Fe17-xAlx solid solutions and Ce2Fe14Si3, show two absorption peaks characteristic of the 4f1 and 4f0 configurations of cerium, peaks which indicate that cerium is in a mixed valent state in these compounds. All the XANES spectra have been consistently and excellently fit with one sigmoidal function and two Gaussianbroadened Lorentzian functions. The cerium spectroscopic valence obtained from the relative areas of the two peaks decreases from 3.64 to 3.43 between x=0 and 9 in Ce2Fe17-x,Alx, and correlates linearly with the cerium site volume This correlation confirms that the cerium valence is strongly dependent upon steric effects. In contrast the cerium valence obtained from the XANES spectrum of Ce2Fe14Si3 is not determined by stenc effects and indicates, in agreement with other measurements and calculations, that silicon is more covalently bonded with its near-neighbor cerium atoms than is aluminum. The neodymium LIII,-edge XANES spectra of the Nd2Fe17-x Alx solid solutions, where x is 0, 3, and 8, reveal the presence of only trivalent neodymium and an increase of the empty 5d state density when aluminum is substituted in place of iron. XANES measurements at the iron K edee of the Ce2Fe17-xAlx, and Nd2Fe17-1Alx, solid solutions show changes m the relative intensity of the multiple scattering peaks, changes which are related to the changing composition of the first three neighbor shells with increasing aluminum content

Tests of achromatic phase shifters performed on the SYNAPSE test bench: a progress report

The achromatic phase shifter (APS) is a component of the Bracewell nulling interferometer studied in preparation for future space missions (viz. Darwin/TPF-I) focusing on spectroscopic study of Earth-like exo-planets. Several possible designs of such an optical subsystem exist. Four approaches were selected for further study. Thales Alenia Space developed a dielectric prism APS. A focus crossing APS prototype was developed by the OCA, Nice, France. A field reversal APS prototype was prepared by the MPIA in Heidelberg, Germany. Centre Spatial de Li\`ege develops a concept based on Fresnel's rhombs. This paper presents a progress report on the current work aiming at evaluating these prototypes on the SYNAPSE test bench at the Institut d'Astrophysique Spatiale in Orsay, France

An illumination device formed by cutting and laminating coated plates

publication date: 2004-10-20; filing date: 2003-04-16An illumination device based on multi facet plastic optics is proposed.The fabrication principle is novative and based on specific cutting geometry and coating laminatio

Antireflective subwavelength patterning of IR optics

peer reviewedThermal infrared (IR) lenses require efficient anti-reflection coating. Moth-eye (or egg-box) 2D subwavelength gratings have demonstrated their ability to reach a very high transmission for a wide wavelength and angular range. The use in thermal IR is simplified by the lower resolution for lithographic technology, compared to visible waveband. However, deeper structures must be engraved and lithography must be adapted to IR materials. In order to be cost-effective, the patterning must be produced by replication techniques, such as embossing. Our laboratory is now experimenting hot embossing of moth-eye patterns in chalcogenide substrates. In this paper, theoretical analysis, micro-lithographic technology and manufacturing processes are detailed

Direct assembly of cyclic olefin copolymer microfluidic devices helped by dry photoresist

A generic method for rapid, reproducible, and robust selective bonding of microfluidic chips made of Cyclic Olefin Copolymer (COC) has been developed and optimized. In this work we propose an adhesive bonding technique using ORDYL negative dry film photo-resist as glue to perform the packaging of COC micro-patterned structures. The ORDYL resist is qualified in terms of resolution, biocompatibility and fluidic sealing. The adhesive bonding is achieved by laminating a thin layer of ORDYL SY300 (70%)

Portable Holographic Marking Unit

publication date: 2003-09-04; filing date: 2003-02-2

Method for manufacturing an improved optical layer of light emitting device with surface nano-micro texturation based on coherent electromagnetic radiation speckle lithography

publication date: 2012-05-30; filing date: 2010-11-24An object of the present invention is to provide a cheap, rapid, controlled, reproducible and polyvalent method for manufacturing a light emitting device with an internal source of light capable of achieving an enhancement in extraction efficiency. The invention proposes a method for manufacturing an optical layer for a light emitting device having an internal source of light and an optical layer separating the internal source of light and an external medium of light diffusion, wherein the method comprises the use of coherent electromagnetic radiation speckle lithography, such as laser speckle lithography, to make a nano/micro texturation on at least one surface of the optical laye

Mössbauer Spectral Evidence for Rhombohedral Symmetry in R₃Fe₅O₁₂ Garnets with R = Y, Eu and Dy

The iron-57 Mossbauer spectra of R3Fe5O12, where R is Y, Eu and Dy, have been measured between 4.2 and 550 K. The substantial quadrupole splittings observed in the paramagnetic spectra confirm that the local symmetry at both the tetrahedral and octahedral iron(III) sites is not cubic. The low temperature Mossbauer spectra of Dy3Fe5O12 clearly confirm the spin reorientation between 10 and 15 K and the 4.2 and 10 K spectra are consistent with the known orientation of the magnetization at 14 K in the cubic Ia3-d unit cell. The Mossbauer spectra of R3Fe5O12, where R is Y, Eu and Dy, obtained between 45 and 295 K, reveal four different tetrahedral iron(III) Mossbauer spectral components, four components which are inconsistent with a magnetization oriented along the [111] axis of a cubic Ia3-d unit cell. In contrast, these four components are consistent with a crystal symmetry which is reduced from cubic to rhombohedral R3-. The temperature dependence of the hyperfine fields in Dy3Fe5O12 indicates a small biquadratic exchange contribution to the magnetic exchange. The temperature dependence of the isomer shifts in Dy3Fe512 gives Mossbauer lattice temperatures of 405 and 505 K for the 16a and 24d sites, respectively, values which are in excellent agreement with the Debye temperature measured for Y3Fe5O12

IR Diffractive and Reduced Cost Optics for space application

This document reports the investigation of the IR materials. The aim is to evaluate their potential in reducing the fabrication costs while ensuring good optical and mechanical performances in the domain of interest. Suitability for space applications will be reported