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Herzig, Hans-Peter
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Herzig, Hans-Peter
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Voici les éléments 1 - 10 sur 35
- PublicationAccès libreElement-sensitive X-ray imaging and computed tomography using energy-selective photodetection(2010)
; ; Stoeckli-Evans, H.A new method in X-ray imaging is presented and a proof of concept shown. The proof of concept is done with the simultaneous identification of aluminum, silicon and titanium and the determination of its integrated density. Also some additional measurements are conducted with aqueous solutions. In this case the concentration of sodium chloride and calcium chloride is measured. The method works in transmission and with a spectral analysis of the absorbed photons. The result is an elemental distribution in the path of the X-ray photons. The concept has no strict limit of the number of elements simultaneously detectable. In this work only a single spectrometer is used. The detector can be extended to an array of spectrometers. The method can also be combined with tomography. In this case it is possible to calculate the density of the elements in the voxels of the reconstruction. The method works in photoabsorption and is therefore optimized for thin biological samples. Experiments conducted are in the energy range of 10 – 13 keV using a X-ray source with 15 kVp and with a broad spectrum. The sample can be kept under standard conditions which allows measurements on living tissue. Fine effects on the mass-absorption coefficients are measured in order to identify the elements. Because these fine effects are difficult to detect the stability of the system is important. The elemental distribution information can be used to increase the contrast of some conventional images or to identify tissues, cells, or even molecules. Therefore functional informations could be added to the images. This would be a strong increase in the practical value of X-ray images. - PublicationAccès librePolymer multilayer photonic micro- and nanostructures with tailored spectral propertiesAmazing and beautiful optical effects are present in Nature. Some examples are the iridescent colors produced by peacocks, butterflies and beetles. While the simulations of some of these structures have already been realized, only a few elements have been fabricated. We are interested to understand and to reproduce some of these amazing optical properties. Applications such as security or decorative elements in different fields like jewelery or horology can be imagined. SEM pictures of the structure of these animals show a frequent combination of periodic or pseudo-periodic elements such as interference filters, multilayer reflectors, microlenses and gratings. The different elements combine angular and spectral effects. This combination enables strong optical effects for a large range of viewing angles and spectra. Different technologies such as standard photolithography, recording of interference patterns, transfer of photoresist structures in glass substrates, replications, hot embossing and spincoating were used to fabricate a variety of optical elements. The fabricated elements were produced with polymer materials because of their ease of use, and the possibility to build multilevel structures with replication methods. A drawback is the small refractive index difference possible between polymers and compared to air.
In the first part, different combinations of polymer micro- and nano-optical elements such as corrugated gratings, multilayer Bragg reflectors, microlens arrays, micro-prisms arrays and diffusers were successfully fabricated. Poly (vinyl alcohol) and poly (N-vinycarbazole) with refractive indices of 1.56 and 1.72, respectively, at a wavelength of 500nm were used to fabricate the polymer multilayer reflectors. The micro-optical elements used were: microlenses with diameter between 32 μm and 250 μm and around 20 μm height; prisms with 50 μm period and 25 μm height. The angularly dependent reflectivity of the different fabricated elements was studied. Thanks to the close combination of diffractive, refractive and reflective micro- and nano-optical elements, non-standard artificial visual color effects were produced. The fabricated elements were modeled with different tools according to the dimensions of the different optical elements. Ray tracing analysis was used in the case with micro-optical elements while the Fourier modal method permitted simulation of the interaction of the light with the periodic nano-structures. The specific effects of the variation of the different parameters were highlighted, the basic principles and the limitation of the polymer technology were identified.
In the second part, the optical modeling tools and the fabrication technologies developed were used to model and fabricate polymer light emitting diodes in a distributed feedback regime. The optical properties of the different layers were modeled and the physical dimensions of elements with active conductive polymers me-LPPP and F8 were calculated, fabricated and tested. The sensitive dimensions and parameters were underlined.
Polymer materials permitted rapid fabrication of complex and innovative optical elements with very simple technologies like spin-coating and replication methods. These technologies allow the combination of nano-optical elements with dimensions of the order of a hundred nanometers with micro-optical elements with dimension of the order of about ten to one hundred microns. - PublicationAccès libreHigh Resolution Interference Microscopy: A Tool for Probing Optical Waves in the Far-Field on a Nanometric Length Scale(2006)
; High Resolution Interference Microscopy (HRIM) is a technique that allows the characterization of amplitude and phase of electromagnetic wave-fields in the far-field with a spatial accuracy that corresponds to a few nanometers in the object plane. Emphasis is put on the precise determination of topological features in the wave-field, called phase singularities or vortices, which are spatial points within the electromagnetic wave at which the amplitude is zero and the phase is hence not determined. An experimental tool working in transmission with a resolution of 20 nm in the object plane is presented and its application to the optical characterization of various single and periodic nanostructures such as trenches, gratings, microlenses and computer generated holograms is discussed. The conditions for the appearance of phase singularities are theoretically and experimentally outlined and it is shown how dislocation pairs can be used to determine unknown parameters from an object. Their corresponding applications to metrology or in optical data storage systems are analyzed. In addition, rigorous diffraction theory is used in all cases to simulate the interaction of light with the nano-optical structures to provide theoretical confirmation of the experimental results. - PublicationAccès libreHigh-resolution measurement of phase singularities produced by computer-generated holograms(2004)
; We present measurements of the intensity as well as the phase distribution in the various diffraction orders of computer-generated holograms designed to generate a higher order Gauss–Laguerre beam. For the direct measurement of the phase distribution in the diffraction orders a high-resolution interferometer is used, which allows access to a lateral length scale for the localization of phase singularities below the wavelength. It is experimentally shown that in beams that carry multiple singularities, the dislocations do not degenerate. This effect cannot be seen by analyzing only the intensity distribution of the laser beam. - PublicationAccès libreAdvanced label-free biochemical sensors based on integrated optical waveguide gratings: theory, modeling, design and characterization(2004)
- PublicationAccès libreDiffractive and refractive lenses for hard x-rays with ultra-high efficiencies(2004)
- PublicationAccès libreApplications of Diffractive and Micro-Optics in Lithography(2004)
- PublicationAccès librePropagation of the electromagnetic field in fully coated near-field optical probes(2003)
; Fully metal-coated near-field optical probes, based on a cantilever design, have been studied theoretically and experimentally. Numerical simulations prove that these structures allow nonzero modal emission of the electromagnetic field through a 60-nm-thick metallic layer, that is opaque when deposited on flat substrates. The far-field intensity patterns recorded experimentally correspond to the ones calculated for the fundamental and first excited LP modes. Moreover, this study demonstrates that a high confinement of the electromagnetic energy can be reached in the near-field, when illuminated with radially polarized light. Finally, it was verified that the confinement of the field depends on the volume of the probe apex. - PublicationAccès libreMicro-optical fiber switch for a large number of interconnects using a deformable mirror(2002)
; In this letter, we demonstrate the limitations for 1 × N free space optical switch with a moving macro-lens. We use a deformable mirror to overcome these limitations. The adaptive mirror corrects for the aberrations. Power coupling efficiencies between 6 and 3 dB (including losses due to the optical elements) are feasible for an optical switch allowing up to 3019 receiver fibers. - PublicationAccès libreOptical MEMS based on silicon-on-insulator (SOI) for monolithic microoptics(2002)
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