Showing papers by "Howard A. Padmore published in 2009"

A dedicated superbend x-ray microdiffraction beamline for materials, geo-, and environmental sciences at the advanced light source.

Abstract: A new facility for microdiffraction strain measurements and microfluorescence mapping has been built on beamline 12.3.2 at the advanced light source of the Lawrence Berkeley National Laboratory. This beamline benefits from the hard x-radiation generated by a 6 T superconducting bending magnet (superbend). This provides a hard x-ray spectrum from 5 to 22 keV and a flux within a 1 microm spot of approximately 5x10(9) photons/s (0.1% bandwidth at 8 keV). The radiation is relayed from the superbend source to a focus in the experimental hutch by a toroidal mirror. The focus spot is tailored by two pairs of adjustable slits, which serve as secondary source point. Inside the lead hutch, a pair of Kirkpatrick-Baez (KB) mirrors placed in a vacuum tank refocuses the secondary slit source onto the sample position. A new KB-bending mechanism with active temperature stabilization allows for more reproducible and stable mirror bending and thus mirror focusing. Focus spots around 1 microm are routinely achieved and allow a variety of experiments, which have in common the need of spatial resolution. The effective spatial resolution (approximately 0.2 microm) is limited by a convolution of beam size, scan-stage resolution, and stage stability. A four-bounce monochromator consisting of two channel-cut Si(111) crystals placed between the secondary source and KB-mirrors allows for easy changes between white-beam and monochromatic experiments while maintaining a fixed beam position. High resolution stage scans are performed while recording a fluorescence emission signal or an x-ray diffraction signal coming from either a monochromatic or a white focused beam. The former allows for elemental mapping, whereas the latter is used to produce two-dimensional maps of crystal-phases, -orientation, -texture, and -strain/stress. Typically achieved strain resolution is in the order of 5x10(-5) strain units. Accurate sample positioning in the x-ray focus spot is achieved with a commercial laser-triangulation unit. A Si-drift detector serves as a high-energy-resolution (approximately 150 eV full width at half maximum) fluorescence detector. Fluorescence scans can be collected in continuous scan mode with up to 300 pixels/s scan speed. A charge coupled device area detector is utilized as diffraction detector. Diffraction can be performed in reflecting or transmitting geometry. Diffraction data are processed using XMAS, an in-house written software package for Laue and monochromatic microdiffraction analysis.

A fast, direct x-ray detection charge-coupled device

Abstract: A charge-coupled device (CCD) capable of 200 Mpixels/s readout has been designed and fabricated on thick, high-resistivity silicon. The CCDs, up to 600 μm thick, are fully depleted, ensuring good infrared to x-ray detection efficiency, together with a small point spread function. High readout speed, with good analog performance, is obtained by the use of a large number of parallel output ports. A set of companion 16-channel custom readout integrated circuits, capable of 15 bits of dynamic range, is used to read out the CCD. A gate array-controlled back end data acquisition system frames and transfers images, as well as provides the CCD clocks.

The optics beamline at the Swiss Light Source

Abstract: We present the successful installation and the performance of a new beamline for optics and instrumentation research and developments at the Swiss Light Source. The beamline covers the photon energy range from 5.5 to 22.5 keV at a bending magnet with a cryogenically cooled Si(1 1 1) channel cut monochromator followed by a bendable toroidal mirror with 1:1 focusing. Monochromator and focusing mirror can be retracted independently to allow monochromatic and pink beam mode with and without focusing. In focused monochromatic mode we measured a usable photon flux of 2 × 10 11 photons/s at 11 keV within a focus of 70 μ m × 140 μ m (FWHM v × h ). The higher order contamination has been determined with absorption foils. We measured 0.025% of second order light at 9 keV and 17% of third order contamination at 6 keV. In pink beam mode we measured with a thermopile sensor a radiation power of 10.6 W for 1 mrad acceptance.

Design Studies for a VUV–Soft X-ray Free-Electron Laser Array

Abstract: Several recent reports have identified the scientific requirements for a future soft X-ray light source [1, 2, 3, 4, 5], and a high-repetition-rate free-electron laser (FEL) facility responsive to them is being studied at Lawrence Berkeley National Laboratory (LBNL) [6]. The facility is based on a continuous-wave (CW) superconducting linear accelerator with beam supplied by a high-brightness, high-repetition-rate photocathode electron gun operating in CW mode, and on an array of FELs to which the accelerated beam is distributed, each operating at high repetition rate and with even pulse spacing. Dependent on the experimental requirements, the individual FELs may be configured for either self-amplified spontaneous emission (SASE), seeded high-gain harmonic generation (HGHG), echo-enabled harmonic generation (EEHG), or oscillator mode of operation, and will produce high peak and average brightness X-rays with a flexible pulse format ranging from sub-femtoseconds to hundreds of femtoseconds. This new light s...

5000 Groove/mm multilayer-coated blazed grating with 33% efficiency in the 3rd order in the EUV wavelength range

Abstract: We report on recent progress in developing diffraction gratings which can potentially provide extremely high spectral resolution of 105-106 in the EUV and soft x-ray photon energy ranges. Such a grating was fabricated by deposition of a multilayer on a substrate which consists of a 6-degree blazed grating with a high groove density. The fabrication of the substrate gratings was based on scanning interference lithography and anisotropic wet etch of silicon single crystals. The optimized fabrication process provided precise control of the grating periodicity, and the grating groove profile, together with very short anti-blazed facets, and near atomically smooth surface blazed facets. The blazed grating coated with 20 Mo/Si bilayers demonstrated a diffraction efficiency in the third order as high as 33% at an incidence angle of 11° and wavelength of 14.18 nm. This work was supported by the US Department of Energy under contract number DE-AC02-05CH11231.

R&D for a Soft X-Ray Free Electron Laser Facility

Abstract: R&D for a Soft X-Ray Free Electron Laser Facility A White Paper Report prepared by LBNL and SLAC with contributions from LBNL: David Attwood, John Byrd, John Corlett, Peter Denes, Roger Falcone, Phil Heimann, Wim Leemans, Howard Padmore, Soren Prestemon, Fernando Sannibale, Ross Schlueter, Carl Schroeder, John Staples, Marco Venturini, Tony Warwick, Russell Wells, Russell Wilcox, and Alexander Zholents SLAC: Chris Adolphsen, John Arthur, Uwe Bergmann, Yunhai Cai, Eric Colby, David Dowell, Paul Emma, John Fox, Josef Frisch, John Galayda, Robert Hettel, Zhirong Huang, Nan Phinney, Tom Rabedeau, Tor Raubenheimer, David Reis, John Schmerge, Joachim Stohr, Gennady Stupakov, Bill White, and Dao Xiang Lawrence Berkeley National Laboratory SLAC National Accelerator Laboratory June 2009

Optical path function calculation for an incoming cylindrical wave

Abstract: Modern polishing methods of ion-beam milling, and single atom removal techniques are beginning to allow the fabrication of arbitrary surface shapes for reflecting grazing incidence optics. Moreover, the total expense of fabrication, coating, measuring, mounting, aligning, cooling, and surrounding the optic with vacuum make the reduction of optical part count attractive for the latest generation x-ray sources, not even considering potential effects on the scattering and reflective losses of the radiation. These two developments converge to effectively suggest the question of what surface would be the optimally de-magnifying surface to replace a toroid illuminated by a wave cylindrical in the sagittal direction if the sag of the single surface were determined by a function, and not constrained to be a typical optical shape. To address this we derive a simplified case of the formalism of Chrisp, using the classical optical path function approach of Fermat to give a power series calculation of this best surface. This surface, the "diaboloid," would in principle earn its name by its, at least ab initio, consideration of being very difficult to manufacture. We show an example of improvement this surface would provide.

Ultra-high Resolution Optics for EUV and Soft X-ray Inelastic Scattering

Abstract: We describe a revolutionary new approach to high spectral resolution soft x-ray optics. Conventionally in the soft x-ray energy range, high spectral resolution is obtained by use of a relatively low line density grating operated in 1st order with small slits. This severely limits throughput. This limitation can be removed by use of a grating either in very high order, or with very high line density, if one can maintain high diffraction efficiency. We have developed a new technology for achieving both of these goals which should allow high throughput spectroscopy, at resolving powers of up to 106 at 1 keV. Such optics should provide a revolutionary advance for high resolution lifetime free spectroscopy, such as RIXS, and for pulse compression of chirped beams. We report recent developmental fabrication and characterization of a prototype grating optimized for 14.2 nm EUV light. The prototype grating with a 200 nm period of the blazed grating substrate coated with 20 Mo/Si bilayers with a period of 7.1 nm demonstrates good dispersion in the third order (effective groove density of 15,000 lines per mm) with a diffraction efficiency of more than 33percent.