Bragg-Fresnel Lens Research Articles

Two-dimensional X-ray microfocusing using a curved crystal Bragg-Fresnel lens

A two-dimensional focusing element based on a curved crystal Bragg-Fresnel lens was designed and successfully tested in the X-ray energy range of 15–20 keV on the Optics Beamline at the ESRF. A 4.5 × 9.1 μm 2 wide focal spot was observed at 17.2 keV. The intensity in the focal spot was two orders of magnitude higher with respect to a flat linear Bragg-Fresnel lens.

Multilayer zone plate and Bragg-Fresnel lens for focusing hard X-rays

Multilayer zone plate and Bragg-Fresnel lens for focusing hard X-rays

Effects of the Microstructuring Process on Diffraction Properties of Bragg–Fresnel Lenses

The effects appearing in a crystal microstructuring by reactive ion etching on diffraction properties of Bragg–Fresnel lenses were studied. Possible deviations of the real zone structures from ideal ones were considered. The influence of the Fresnel zone displacements due to sidewall undercutting effects and due to a mask erosion was analyzed. Technological tolerances for a different zone profile shape were defined.

Ion implanted Bragg–Fresnel lens

We have investigated the feasibility of widening the bandpath of the Bragg–Fresnel optical element through the use of ion implantation. The focusing properties of Bragg–Fresnel lenses (BFLs) were studied as a function of the implantation dose and energy. An enhancement of the focus intensity of up to 15% was found, which is less than expected. Due to the complicated scattering of the low energy ions inside the micrometer- and submicrometer-sized crystal features that make up the BFL relief, the implantation technology destroys the peripheral zones of the BFL more than it increases the intensity in the focus. Nevertheless we believe that high energy implantation can be successfully used to modify the BFL reflectivity, especially in the case of nearly backscattering reflection.

Imaging Complex Fluids Under Confinement and Flow: Development of Bragg-Fresnel Optics for X-ray Microdiffraction

ABSTRACTWe present results of simultaneous efforts to develop: 1.) Bragg-Fresnel Optics(BFO) to be used in X-ray microdiffraction methods, in particular as applied to structural studies of complex fluids and biomaterials under confinement and flow conditions; and 2.) Methodologies for confining complex fluids and biomaterials for in-situ structural studies. Using microelectronics process technology, we have fabricated linear and circular Bragg-Fresnel Lenses (BFL) in Si and III-V compound semiconductor substrates such as InP, GaAs and GaAs heterostructures with outermost zone width to 0.25 μm. X-ray characterization of linear BFLs were performed on a wiggler beamline at Stanford Synchrotron Radiation Laboratory (SSRL) at x-ray energies of 8 keV and 16 keV. A ∼5 μm focal spot size was obtained with a 50 μm incident beam, which was determined by the partial coherence of the source. On the confinement techniques, we have developed the X-ray Surface Force Apparatus (XSFA) which allows in-situ x-ray diffraction measurements to be made on fluid thin films confined between two atomically smooth surfaces. A new approach is being pursued to study the effects of confinement and flow on complex fluids and biological materials using microchannels fabricated on glass substrates.

Effects of the Microstructuring Process on Diffraction Properties of Bragg-Fresnel Lenses

The effects appearing in a crystal microstructuring by reactive ion etching on diffraction properties of Bragg-Fresnel lenses were studied. Possible deviations of the real zone structures from ideal ones were considered. The influence of the Fresnel zone displacements due to sidewall undercutting effects and due to a mask erosion was analyzed. Technological tolerances for a different zone profile shape were defined.

Nanofabrication of Multilayer Zone Plates by Helicon Plasma Sputtering

Multilayer zone plates whose outermost zone widths are less than 100 nm have been fabricated. Alternate deposition of Ag and Al layers has been performed using a helicon plasma sputtering technique, in which Ar gas pressure was less than 1×10-3 Torr, which is one order lower than in conventional magnetron sputtering. More than 100 Ag/Al layers were deposited, with the thickness of each layer being monitored and controlled by a computer. The multilayered plane was sliced vertically and thinned after the deposition. The multilayer zone plate combined with a crystal acts as a monochromatizing and focusing device for hard X-rays, i.e., a Bragg-Fresnel lens.

Diffraction of a focused X-ray beam by surface acoustic waves

This paper reports the first attempt to carry out a focusing followed by a space-time scanning of a synchrotron X-ray beam. The focusing is performed through an elliptical multilayer Bragg-Fresnel lens while the space-time scanning is due to the grazing incidence diffraction on the YZ-cut of a LiNbO 3 crystal modulated by pulsed surface acoustic waves. It opens the field of a new generation of X-ray beam control devices which should be of interest for X-ray scanning microscopy or time resolved spectroscopy. These experiments were carried out at LURE (Orsay, France).

Emittance monitors based on Bragg–Fresnel lenses

Two different setups for imaging an undulator source in the x-ray range have been tested. In the first, two circular Bragg–Fesnel lenses (BFL) were combined to form a telescope. The second consisted of one circular BFL and an asymmetrically cut crystal which produced vertical magnification. The emittance of the electron beam ε can then be deduced from the measured size of the source σ and the knowledge of the beta function at the source: ε=σ2/β. Effects were observed due, on the one hand, to the small aperture of the BFL and, on the other hand, to the angular emission pattern from an undulator.

Testing of submicrometer fluorescence microprobe based on Bragg–Fresnel crystal optics at the ESRF

An x-ray fluorescence microprobe with circular Bragg–Fresnel lens was tested at the European Synchrotron Radiation Facility Microfocus beamline. A focal spot of 0.7 μm was observed using the knife-edge technique at the energy 7.6 keV (wavelength 1.6 Å). The intensity in the focal spot was measured to 108 ph/s in energy bandwidth of 10−5. The fluorescence microprobe was applied for mapping 100 μm size micrometeorite at 13.5 keV.

Microplasma object imaging spectroscopy by using zone plate surface structure on mica crystal

A new method is proposed for obtaining spatially resolved multicharged ion spectra of microplasma sources with resolution better than 0.5 μm. The method is based on making a Bragg–Fresnel lens structure on a mica crystal surface. The lens was formed in a direction normal to the direction of dispersion and was used for the investigation of plasma created in nanosecond X pinch. The method may be used in studies of plasma heated by pico- and femtosecond laser radiation.

Reactive ion etching of silicon submicron-sized trenches in SF 6/C 2Cl 3F 3 plasma

Reactive ion etching (RIE) of silicon with thin AZ 1350 and PMMA etch masks in SF 6/C 2Cl 3F 3 plasma is studied. Anisotropic selective etching of silicon with PMMA mask is found. RIE of submicron-sized trenches into silicon with AZ and PMMA masks is investigated under etch conditions typical for high anisotropy. It is shown, that etch rate and etched profile of trenches depend on aspect ratio. Highly anisotropic etching of silicon submicron-sized trenches with selectivity of silicon to PMMA mask of about 10 is developed and used for the fabrication of silicon phase Bragg-Fresnel lenses for hard x-rays.

X-Ray Point Focusing Using Cylindrically Bent Crystals with Modulated Structures for Synchrotron X-Ray Beams

Micron or submicron spatial resolution for x-ray microfluorescence analysis has been pursued using various x-ray point focusing methods,1-4 such as transmission zone plates, tapered capillaries, and Bragg Fresnel lenses. Point focusing using bent crystals does not seem to be a desirable means for achieving a microbeam size, although it is a traditional technique which utilizes perfectly curved crystal surfaces to focus x rays emanating from the source. It is known that point focusing can only be achieved by bending a crystal two dimensionally, which normally introduces imperfections to the crystal since the crystal is an undevelopable surface. Unavoidably, the introduced imperfections will broaden the reflection curve (rocking curve) of the crystal and, in turn, broadens the focal spot size.

Imaging of an undulator source by phase circular Bragg-Fresnel lenses

Focusing properties and heatload resistance of a Bragg-Fresnel lens placed in an undulator beam have been demonstrated. The electron beam at an undulator source has been imaged by two setups using Bragg-Fresnel lenses. The first setup is a two-lenses telescope and the second one consists of one circular BFL and an asymmetrically cut crystal

2D imaging of an undulator source by phase circular Bragg–Fresnel lens

Two-dimensional imaging of an undulator x-ray source at different photon energies has been observed by means of phase circular Bragg–Fresnel lens (BFL) at the ESRF ID6 beamline. The optical properties of the BFL in the energy range 6–18 keV have been studied. Imaging has been studied on various orders of diffraction and on various harmonics of the undulator spectrum. Good resistance to a heatload of 100 W and 12 W/mm2 in the white beam has been demonstrated.

Elliptical multilayer Bragg-Fresnel lenses with submicron spatial resolution for X-rays

Elliptical Bragg-Fresnel multilayer lenses (BFML), designed and fabricated at the Institute of Microelectronic Technology (Russian Academy of Science) have been used for two-dimensional focusing of the white X-ray synchrotron beam at LURE (Orsay France). For two fixed beam energies (8 keV and 12.4 keV), the spot size produced was approximately 1 μm as determined from a high resolution photographic plate. A fluorescence X-ray scanning microprobe based on these BFML lenses was also tested. The transmitted signal registered during the scan of a test object shows less than 1 μm resolution with 8 keV output photon energy. 2D scanning images with submicron resolution of test objects in transmission mode at 8 keV and 12.4 keV beam energies are presented.

A double focusing SAXS camera with µm focal spot based on a circular bragg-fresnel lens

A 2D focusing SAXS camera has been build based on a circular Bragg-Fresnel lens. The camera has been tested at the Microfocus beamline at the European Synchrotron Radiation Facility. An undulator was used as radiation source. The focused beam size at the sample position of about 1,5 * 2 μm 2 and intensity of about 109 photons/s was obtained at a wavelength of 1.24A (10keV). A Molecular Dynamics image plate was used to detect the low -angle diffraction pattern. For native turkey leg tendon collagen intermediate areas between the calcified and non-calcified regions were analysed. More than 22 orders including the first order peak were clearly resolved

Imaging spectroscopy of microscopic plasmas by means of a mica crystal with a zone-plate surface structure

A method is proposed for obtaining spectra with a high spatial resolution, as high as 0.5 μm. The method involves fabricating a Bragg–Fresnel lens on the surface of a mica crystal. The lens is formed in the direction perpendicular to the dispersion direction. A structure of this sort has been fabricated and has been used to record spectra of the plasmas of Z- and X-pinches. Bragg–Fresnel lenses on crystal surfaces are of much interest for studying the dimensions of the x-ray emission of multiply charged ions formed in plasmas heated by picosecond- and femtosecond-range lasers.

Bragg–Fresnel lens with the slope zone structure

The effect of the one-dimensional x-ray focusing by a linear Bragg-Fresnel lens (BFL) with the slope zone structure has been found theoretically to exist in a meridional diffraction layout. Optimization of the BFL spatial configuration was carried out. This BFL was fabricated, applying the results of simulations.

Kirkpatrick–Baez microprobe on the basis of two linear single crystal Bragg–Fresnel lenses

X-ray microprobe on the basis of two linear single crystal phase Bragg–Fresnel lenses in Kirkpatrick–Baez geometry has been suggested and realized for hard x rays. The Kirkpatrick–Baez optics has been tested by two-dimensional imaging the x-ray source spot of a conventional sealed-off x-ray tube with Cu target (λ=1.54 Å). The possibility of applying this kind of microprobe at a synchrotron radiation source is discussed.