Roger J. Dejus

XOP: recent developments

XOP (X-ray OPtics utilities) is a graphical user interface (GUI) to run computer programs that calculate basic information needed by synchrotron radiation beamline scientists and engineers. It can also be used as a front end for specific codes or packages for data analysis and data reduction (XAFS, surface crystallography, etc.). XOP contains a customized database for optical and atomic constants. It has a flexible design and new applications may be added. The capabilities of XOP, including those related to simulations of crystal diffraction profiles and multilayer reflectivities, are summarized. We discuss the most recent developments to be included in XOP version 2.0. A few other examples of typical calculations are: insertion device (undulator and wiggler) spectra and angular distributions, mirror and multilayer reflectivities, and crystal diffraction profiles. The computer programs are executed and the results are analyzed within the GUI, which makes them fast and easy to use. The XOP interface is written in the Interactive Data Language (IDL) from Research Systems Inc., and it runs on the Unix (HP, Sun, Linux, DEC-Alpha, and Silicon Graphics), and on the Windows 95/NT operating systems. It has been built with an IDL license embedded and is available under some limited conditions free of charge from the authors.

Status of XOP: an x-ray optics software toolkit

XOP is a user-friendly computer environment for performing calculations of interest to the synchrotron radiation community. It provides codes for: i) modeling x-ray sources (e.g., synchrotron sources, such as undulators and wigglers), ii) calculating characteristics of optical elements (mirrors, filters, crystals, multilayers, etc.), and iii) multipurpose data visualization and analyses. The XOP functionality can be extended with external plug-ins (extensions). We describe the status of XOP including recent developments in the current version (XOP 2.11). Plans for the future will also be presented.

XOP: a multiplatform graphical user interface for synchrotron radiation spectral and optics calculations

XOP (X-ray OPtics utilities) is a graphical user interface (GUI) created to execute several computer programs that calculate the basic information needed by a synchrotron beamline scientist (designer or experimentalist). Typical examples of such calculations are: insertion device (undulator or wiggler) spectral and angular distributions, mirror and multilayer reflectivities, and crystal diffraction profiles. All programs are provided to the user under a unified GUI, which greatly simplifies their execution. The XOP optics applications (especially mirror calculations) take their basic input (optical constants, compound and mixture tables) from a flexible file-oriented database, which allows the user to select data from a large number of choices and also to customize their own data sets. XOP includes many mathematical and visualization capabilities. It also permits the combination of reflectivities from several mirrors and filters, and their effect, onto a source spectrum. This feature is very useful when calculating thermal load on a series of optical elements. The XOP interface is written in the IDL (Interactive Data Language). An embedded version of XOP, which freely runs under most Unix platforms (HP, Sun, Dec, Linux, etc) and under Windows95 and NT, is available upon request.

Structure of vitreous AgGeSe

Pulsed neutron diffraction has been used to study the short- and intermediate-range order of vitreous g-Ag 4 Ge 3 Se 9 . By utilizing the techniques of isotopic substitution and temperature variation, it has been possible to estimate four of the six partial pair-distribution functions for the first coordination shells. Measurements at T = 10 K extending out to wavevectors Q ≈ 34 A −1 provide accurate results for the bond lengths and coordination numbers. Comparison is also made with results derived from a variant of the maximum entropy method. Ge is fourfold-coordinated by Se at an average interatomic distance of 2.37 ± 0.005 A which is consistent with the GeSe 4/2 tetrahedron also being a structural unit in the Ag-doped Ge Se glass. Ag is predominantly bonded to Se at an average distance of 2.68±0.01 A and is threefold-coordinated. This low coordination might be a key factor in understanding the fast ion motion in this system. The temperature dependence of the structure factor, S ( Q ), and the radial distribution functions were investigated. The Ge Se and Se Se correlations solely reflect increased thermal vibrations of the atoms, whereas the Ag correlations behave quite differently with increasing temperature up to 170°C. The Ag correlations change rapidly and become liquid-like at elevated temperatures reflecting the diffusive motion of Ag. The first sharp diffraction peak at 1.04 A −1 in S ( Q ) exhibits the anomalous temperature dependence typical of chalcogenide glasses in that the peak becomes narrower and increases in amplitude with increasing temperature (∼ 2% from room temperature to 170°C).

XOP v2.4: recent developments of the x-ray optics software toolkit

XOP v2.4 consists of a collection of computer programs for calculation of radiation characteristics of X-ray sources and their interaction with matter. Many of the programs calculate radiation from undulators and wigglers, but others, such as X-ray tube codes, are also available. The computation of the index of refraction and attenuation coefficients of optical elements using user-selectable databases containing optical constants is an important part of the package for calculation of beam propagation. Coupled computations are thus feasible where the output from one program serves as the input to another program. Recent developments including enhancements to existing programs are described.

Intermediate-range order in binary chalcogenide glasses: The first sharp diffraction peak

The structure factor of SiS/sub 2/, SiSe/sub 2/, GeS/sub 2/, and GeSe/sub 2/ glasses, and of GeSe/sub 2/ liquid, have been measured using time-of-flight, pulsed-neutron diffraction. An ubiquitous first sharp diffraction peak (FSDP) appears at /approximately/1 /angstrom//sup /minus/1/ and is a signature of intermediate-range order. In GeSe/sub 2/, the FSDP of the liquid at 1084 K and of the glass at 10 K have the same halfwidth and position in reciprocal space. The origin of the FSDP in these systems is discussed in terms of correlations arising in large ring structures. It is shown that the intensities of the FSDPs scale with coherent scattering from A-A and A-X correlations in the rings (A = Si or Ge; X = S or Se). Departures from simple scaling indicate a change in the ring sizes contributing to the FSDP. 11 refs., 2 figs., 2 tabs.

XOP 2.1 — A New Version of the X‐ray Optics Software Toolkit

X‐ray oriented programs (XOP) is a graphical user‐interface environment for computer codes of interest to the synchrotron radiation community. It provides codes for i) modeling of x‐ray sources (e.g., synchrotron radiation sources, such as undulators and wigglers), ii) calculating characteristics of optical elements (mirrors, filters, crystals, multilayers, etc.), and iii) multipurpose data visualizations and analyses. The current version of XOP (2.0) has been widely distributed at synchrotron facilities and research laboratories. It can be downloaded from http://www.esrf.fr/computing/scientific/xop, and it is also distributed on a CD‐ROM. Today, we count over 400 registered users. We describe recent developments including improved documentation and user interface, and upgraded applications. The functionality of XOP can be extended with external plug‐ins (extensions). We continue to support a visual interface to the SHADOW ray‐tracing program and the multilayer package IMD.

XOP: A graphical user interface for spectral calculations and x‐ray optics utilities

A graphical user interface, using the Interactive Data Language (IDL) widget toolkit, for calculation of spectral properties of synchrotron radiation sources and for interaction of x‐rays with optical elements has been developed. The interface runs presently on three different computer architectures under the Unix operating system – the Sun‐OS, the HP‐UX, and the DEC‐Unix operating systems. The point‐and‐click interface is used as a driver program for a variety of codes from different authors written in different computer languages. The execution of codes for calculating synchrotron radiation from undulators, wigglers, and bending magnets is summarized. The computation of optical properties of materials and the x‐ray diffraction profiles from crystals in different geometries are also discussed. The interface largely simplifies the use of these codes and may be used without prior knowledge of how to run a particular program.

The magnetic and diagnostics systems for the Advanced Photon Source self-amplified spontaneously emitting FEL

A self-amplified spontaneously emitting (SASE) free-electron laser (FEL) for the visible-to-ultraviolet spectral range is under construction at the Advanced Photon Source at Argonne National Laboratory. The amplifier part of the FEL consists of twelve identical 2.7-meter-long sections. Each section includes a 2.4-meter-long, 33-mm-period hybrid undulator, a quadruple lens, and a set of electron beam and radiation diagnostics equipment. The undulatory will operate at a fixed magnetic gap (approx. 9.3 mm) with K=3.1. The electron beam position will be monitored using capacitive beam position monitors, YAG scintillators with imaging optics, and secondary emission detectors. The spatial distribution of the photon beam will be monitored by position sensitive detectors equipped with narrow-band filters. A high-resolution spectrograph will be used to observe the spectral distribution of the FEL radiation.

Measurements of nonlinear harmonic generation at the Advanced Photon Source's SASE FEL

SASE saturation was recently achieved at the Advanced Photon Sources SASE FEL in the low-energy undulator test line (LEUTL) at 530 nm and 385 nm. The electron beam microbunching becomes more and more prominent until saturation is achieved. This bunching causes nonlinear harmonic emission that extends the usefulness of a SASE system in achieving shorter FEL wavelengths for the same electron beam energy. They have investigated the intensity of the fundamental and second-harmonic undulator radiation as a function of distance along the undulator line and present the experimental results and compare them to numerical simulations. In addition, they have measured the single-shot second harmonic spectra as well as the simultaneous fundamental and second harmonic spectra and present the experimental results.