Alan Michette

Modern Developments in X-ray and Neutron Optics

Theoretical Approaches and Calculations.- X-Ray and Neutron Optical Systems.- The BESSY Raytrace Program RAY.- Neutron Beam Phase Space Mapping.- Raytrace of Neutron Optical Systems with RESTRAX.- Wavefront Propagation.- Theoretical Analysis of X-Ray Waveguides.- Focusing Optics for Neutrons.- Volume Effects in Zone Plates.- Nano-Optics Metrology.- Slope Error and Surface Roughness.- The Long Trace Profilers.- The Nanometer Optical Component Measuring Machine.- Shape Optimization of High Performance X-Ray Optics.- Measurement of Groove Density of Diffraction Gratings.- The COST P7 Round Robin for Slope Measuring Profilers.- Hartmann and Shack-Hartmann Wavefront Sensors for Sub-nanometric Metrology.- Extraction of Multilayer Coating Parameters from X-Ray Reflectivity Data.- Refection/Refraction Optics.- Hard X-Ray Microoptics.- Capillary Optics for X-Rays.- Reflective Optical Arrays.- Reflective Optical Structures and Imaging Detector Systems.- CLESSIDRA: Focusing Hard X-Rays Efficiently with Small Prism Arrays.- Multilayer Optics Developments.- Neutron Supermirror Development.- Stress Reduction in Multilayers Used for X-Ray and Neutron Optics.- Multilayers with Ultra-Short Periods.- Specially Designed Multilayers.- Diffraction Optics.- Diffractive-Refractive Optics: X-ray Crystal Monochromators with Profiled Diffracting Surfaces.- Neutron Multiple Reflections Excited in Cylindrically Bent Perfect Crystals and Their Possible use for High-Resolution Neutron Scattering.- Volume Modulated Diffraction X-Ray Optics.- High Resolution 1D and 2D Crystal Optics Based on Asymmetric Diffractors.- Thermal Effects under Synchrotron Radiation Power Absorption.

A Focused Ultrasoft X-Ray Microbeam for Targeting Cells Individually with Submicrometer Accuracy

Abstract Folkard, M., Schettino, G., Vojnovic, B., Gilchrist, S., Michette, A. G., Pfauntsch, S. J., Prise, K. M. and Michael, B. D. A Focused Ultrasoft X-Ray Microbeam for Targeting Cells Individually with Submicrometer Accuracy. Radiat. Res. 156, 796–804 (2001). The application of microbeams is providing new insights into the actions of radiation at the cell and tissue levels. So far, this has been achieved exclusively through the use of collimated charged particles. One alternative is to use ultrasoft X rays, focused by X-ray diffractive optics. We have developed a unique facility that uses 0.2–0.8-mm-diameter zone plates to focus ultrasoft X rays to a beam of less than 1 μm diameter. The zone plate images characteristic K-shell X rays of carbon or aluminum, generated by focusing a beam of 5–10 keV electrons onto the appropriate target. By reflecting the X rays off a grazing-incidence mirror, the contaminating bremsstrahlung radiation is reduced to 2%. The focused X rays are then aimed at selected subcellular targets using rapid automated cell-finding and alignment procedures; up to 3000 cells per hour can be irradiated individually using this arrangement.

Movement and Alignment of Microtubules in Electric Fields and Electric-Dipole-Moment Estimates

The effects of both constant (up to 2 × 103 V/m) and high-frequency alternating fields (up to 2.1 × 105 V/m, 200 kHz to 2 MHz) on suspended microtubules are investigated. At pH 6.8 and 120 mM ionic strength, constant fields cause a motion of microtubules toward the anode. The electrophoretic mobility amounts to 2.6 × 10−4 cm2/Vs, reflecting a negative net charge of approximately 0.2 elementary charges per tubulin dimer. The moving microtubules are randomly space oriented. Alternating high-frequency fields induce electric dipoles and align the microtubules parallel to the field direction. By determining the angular velocity of the turning microtubules, we estimate a dipole moment of roughly 34,000 Debye at 2.1 × 105 V/m and 2 MHz. By comparing the potential energy of the dipole in the applied field with the thermal energy of microtubules, we obtain a minimum value of 6,000 Debye as necessary for an efficient alignment.

Optimisation of depth-graded multilayer coatings for broadband reflectivity in the soft X-ray and EUV regions

Abstract A systematic method which allows the optimum thickness of each layer in a depth-graded multilayer coating to be determined is described. This enables specific reflectivity responses over broad wavelength bands in the soft X-ray and EUV regions to be calculated. The method is applied to the design of some depth-graded molybdenum/silicon multilayers for the wavelength range 13–19 nm, with average normal incidence reflectivities of about 13% in this range, but it is generally applicable for other material pairs and wavelength ranges. In addition, the effects of layer thickness errors on the performance of depth-graded multilayers can be simulated. The model gives better results than those based on power law variation of the layer thicknesses.

Broadband Mo∕Si multilayer transmission phase retarders for the extreme ultraviolet

Experimental results on aperiodic broadband transmission molybdenum/silicon multilayer phase retarders for the extreme ultraviolet range are presented. The broadband phase retarders were designed using a numerical method and made using direct current magnetron sputtering on silicon nitride membrane. The polarization properties of these aperiodic transmission phase retarders have been investigated using the soft x-ray polarimeter at BESSY-II. The measured phase shift was about 42° in the wavelength range of 13.8–15.5nm, and the corresponding s-component transmission (Ts) decreased from 6% to 2% with increasing wavelength.

Examination of the penetration of polymeric methylene di-phenyl-di-isocyanate (pMDI) into wood structure using chemical-state x-ray microscopy

Summary The penetration behaviour of isocyanate-based wood resins was evaluated using x-ray microscopy. Aspen wood pieces were bonded together in a controlled manner. These were embedded in a methacrylate-based resinand thin sections were prepared, cut from the transverse face of thewoodcomposite. X-ray images of these sections were prepared at several selected x-ray energies to allow the isocyanate, cellulose, lignin and the embedding agent distributions to be mapped. The isocyanate resin was found to penetrate deeply into the wood. The resin enters large cell lumen, and wicks along the inner cell wall surfaces. The resin accesses connected cells via connecting pits, which become filled with the resin. The affinity of the isocyanate to the inner surfaces of the large cells is probably due to the hydrophobicity of these surfaces. Isocyanate resins do not penetrate into the smaller parenchyma and tracheid cells and indeed do not even wet the inner surfaces of these cells where isocyanate entry has been allowed due to damage of the cell at the macroscopic surface of the wood. If isocyanates penetrate into the wood-cell walls of the large cells, the concentration in the cell walls has been determined to be less than 2%of the bulk concentration. This lower limit is the sensitivity limit imposed by photon statistics in the data.

Depth-graded multilayer X-ray optics with broad angular response

Abstract A method of designing depth-graded multilayer structures with broad angular response for use as coatings in X-ray optics is presented. The design is based on the well-known Fresnel equations and recursive calculation, combined with a merit function plus random variation of the thickness of each layer. This allows the design of multilayer films for different requirements in X-ray optics. Results are presented on the layer thicknesses in depth-graded W/C multilayer films and their reflectivity as a function of the grazing incidence angle for Cu Kα radiation. The required minimum number of bilayers in depth-graded multilayer films depends on the grazing incidence angle, i.e., the saturation effect observed in the design of periodic multilayer films also emerges in the design of depth-graded multilayers. The predicted performances of multilayers designed using this method are superior to those designed using existing methods.

Two approaches for irradiating cells individually: a charged-particle microbeam and a soft X-ray microprobe

Abstract We are developing two independent, but complementary microbeams for irradiating cells individually in vitro. Firstly, a charged-particle microbeam that uses a fine-bore glass capillary, combined with a transmission detector to precisely irradiate cells with exact numbers of energetic charge-particles and secondly, a soft X-ray microprobe that produces a very fine beam of carbon-K (278 eV) ultrasoft X-rays, focused to a spot size

Soft X-ray contact microscopy using laser plasma sources

The feasibility of using high-power pulsed lasers (several tens of joules per pulse) to produce plasmas as soft X-ray sources for contact microscopy is discussed and demonstrated for a wide range of biological and other material. As in other forms of X-ray microscopy, complicated and probably artefact-inducing specimen preparation is not necessary. The short pulse lengths of the lasers mean that, for single shot exposures, images can be obtained before radiation damage has altered the structure of the specimen, and this higher resolutions are possible, in principle, than for other forms of X-ray microscopy.

Complete polarization analysis of extreme ultraviolet radiation with a broadband phase retarder and analyzer

The polarization state of the BESSY UE56/1-PGM beamline radiation in the broad wavelength range of 12.7–15.5nm was measured using a molybdenum/silicon transmission phase retarder and a reflection analyzer with aperiodic multilayer interference structures, which can broaden the spectral response of these optical elements. The characteristics of the circular polarized undulator radiation, as well as the polarization properties of the two polarizing elements, were determined by a complete polarization analysis. Furthermore, the polarization of the radiation as a function of the undulator shift setting was also measured at the wavelength of 13.1nm by use of the broadband phase retarder-analyzer pair.