Home About us Contact
|
Home About us Contact | ||
|
|
||
Beam Profiles (beam + profile)
Selected AbstractsA comparison of a microfocus X-ray source and a conventional sealed tube for crystal structure determinationJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2009Thomas Schulz Experiments are described in which a direct comparison was made between a conventional 2,kW water-cooled sealed-tube X-ray source and a 30,W air-cooled microfocus source with focusing multilayer optics, using the same goniometer, detector, radiation (Mo,K,), crystals and software. The beam characteristics of the two sources were analyzed and the quality of the resulting data sets compared. The Incoatec Microfocus Source (IµS) gave a narrow approximately Gaussian-shaped primary beam profile, whereas the Bruker AXS sealed-tube source, equipped with a graphite monochromator and a monocapillary collimator, had a broader beam with an approximate intensity plateau. Both sources were mounted on the same Bruker D8 goniometer with a SMART APEX II CCD detector and Bruker Kryoflex low-temperature device. Switching between sources simply required changing the software zero setting of the 2, circle and could be performed in a few minutes, so it was possible to use the same crystal for both sources without changing its temperature or orientation. A representative cross section of compounds (organic, organometallic and salt) with and without heavy atoms was investigated. For each compound, two data sets, one from a small and one from a large crystal, were collected using each source. In another experiment, the data quality was compared for crystals of the same compound that had been chosen so that they had dimensions similar to the width of the beam. The data were processed and the structures refined using standard Bruker and SHELX software. The experiments show that the IµS gives superior data for small crystals whereas the diffracted intensities were comparable for the large crystals. Appropriate scaling is particularly important for the IµS data. [source] Characterisation and cleaning of oxide support materials for cavity ring-down spectroscopyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2010Aras Kartouzian Abstract Cavity ring-down spectroscopy (CRDS) has been applied to characterise different oxide materials (amorphous silica, borosilicate and yttria stabilised zirconia YSZ) which are suitable to be used as support material for size-selected metal clusters. The sensitivity of the spectroscopic method was improved by means of transversal mode matching and spatial filtering of the laser beam profile, reducing the relative error by 50%. The high sensitivity of CRDS allows the detection of trace amounts of impurities and defect sites in the samples, based on their absorption properties. In YSZ, traces of Nd have been detected. The optical quality of the substrates was determined qualitatively according to the measured optical losses. CRDS surface maps have been used to monitor the homogeneity of the support materials, and the influence of ion bombardment on the surface has been studied. It is shown that in the case of BK7® substrates, sputtering with low energy Ar+ ions could remove deposited gold clusters almost completely causing very low damage to the surface. These results were confirmed analytically. [source] Performance of a cryogenic silicon monochromator under extreme heat loadJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2004Aleksandr Chumakov The performance of an indirectly cooled cryogenic silicon monochromator under heat loads up to 870,W has been studied. The investigation was performed over numerous parameters and included measurements of total flux, spectral density, rocking curves, angular beam profiles and crystal slope errors. An almost ideal monochromator performance was observed in the 270,570,W range of the heating power. At a heat load of ,400,W and under standard operation conditions, the crystal distortions did not exceed 1,µrad. At the highest available heat load of 870,W, the crystal distortions were about 7,µrad. [source] Fiber-optic acoustic transducer utilizing a dual-core collimator combined with a reflective micromirrorMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2006Ju-Han Song Abstract A photonic acoustic transducer utilizing a dual-core fiber collimator and a membrane type micromirror was proposed and demonstrated. The collimator and the mirror serve as a compact optical head and a reflective diaphragm, respectively. The micromirror diaphragm is suspended by a silicon bar connected to a frame, allowing for displacement induced by acoustic waves. The optical head incorporating dual collimators integrated in a single housing provides light to and receives it from the diaphragm. It facilitates the initial adjustment of the distance between it and the diaphragm, thanks to its slowly varying beam profiles. For the proposed acoustic transducer, the static characteristics were measured to find the operation point defined as the optimum distance between the head and the diaphragm, and a frequency response with a variation of ,±5 dB was achieved for the range of up to 3 kHz. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1833,1836, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21789 [source] The effect of laser profile, fluence, and spot size on sensitivity in orthogonal-injection matrix-assisted laser desorption/ionization time-of-flight mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2008Hui Qiao The influence of incident laser parameters on sensitivity in matrix-assisted laser desorption/ionization (MALDI) has been investigated using orthogonal-injection time-of-flight (TOF) instruments. A qualitative comparison was first made between the beam profiles obtained with a N2 laser and a Nd:YAG laser using 2-m long optical fibers. The N2 laser gives better sensitivity, consistent with a more uniform fluence distribution and therefore better coverage of the N2 laser profile. Most of the difference disappears when a 30-m long fiber is used or when the fibers are twisted during irradiation to smooth out the fluence distribution. In more systematic measurements, the total integrated ion yield from a single spot (a measure of sensitivity) was found to increase rapidly with fluence to a maximum, and then saturate or decrease slightly. Thus, the optimum sensitivity is achieved at high fluence. For a fluence near threshold, the integrated yield has a steep (cubic) dependence on the spot size, but the yield saturates at higher fluence for smaller spots. The area dependence is much weaker (close to linear) for fluence values above saturation, with the result that the highest integrated yields per unit area are obtained with the smallest spot sizes. The results have particular relevance for imaging MALDI, where sensitivity and spatial resolution are important figures of merit. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||