LEPTOS is a software package for analytical interpretation of data obtained in glancing-incidence X-ray reflectivity and high-resolution X-ray diffraction experiments on thin film structures. The software is designed for comprehensive analysis of physical and crystallographic parameters of modern nanoscale layered structures.
The interpretation is based on up-to-date dynamical diffraction approaches and most recent theories of interaction of X-rays with matter. The graphical user interface (GUI) is designed to conveniently work with experimental data, simulate X-ray scattering processes and automatically fit simulations to the measurements using a sample models.
X-ray Server is a public project operational at the APS since 1997 with the goals to explore novel network technologies for providing wide scientific community with access to personal research results, establishing scientific collaborations, and refining scientific software. The Server provides Web-based access to a number of programs developed by the author in the field of X-ray diffraction and scattering. The software code operates directly on the Server available for use without downloading. Currently seven programs are accessible that have been used more than 85,000 times. This report discusses the Server philosophy, provides an overview of the physical models and algorithms beneath the codes and demonstrates some applications of the programs. It is shown with examples and statistics how the Server goals are achieved. The plans for further X-ray Server development are outlined.
We present a Monte-Carlo algorithm for the simulation of Bragg diffraction from imperfect crystals that are used for neutron analysers and monochromators. The algorithm is used in ray-tracing simulation of neutron instruments but can also be used for x-rays. This method performs a detailed description of the particle interaction with the microscopic regions composing the crystal. It computes important quantities that cannot be calculated with standard models, as the number of multiple scattering events, and diffraction topographs. We also discuss applications of this method to the analysis of x-ray data from mosaic copper crystals.
We report on the feasibility study of a Laue lens for hard X-rays
(> 60 keV) based on mosaic crystals, for astrophysical applications.
In particular we discuss the scientific motivations, its functioning principle, the procedure followed to select the suitable crystal materials, the criteria adopted to establish crystal dimensions and their distribution on the lens in order to obtain the best lens focusing capabilities, and the criteria for optimizing the lens effective area in a given passband. We also discuss the effects of misalignments of the crystal tiles due to unavoidable mechanical errors in assembling the lens. A software was developed to face all these topics and to evaluate the expected lens performance.
X rays focusing telescopes, composed of several Wolter I nested mirror shells reflecting at grazing incidence, are commonly employed only in the soft x-rays band (below 10 keV). At higher energies only direct view detectors (with low or not at all imaging capabilities) have been operative so far. The use of multilayer coatings on Wolter I mirrors can be a suitable way to realize focusing optics operating at higher energies (10 - 100 keV). A procedure based on an iterated simplex numerical method has been developed in order to get a global optimization of the multilayer reflectors sequences that will be applied for this kind of hard X-ray focusing telescopes. In particular, the specific case of the multilayer optimization for the optics of some future X-ray missions has been investigated.
A raytracing code for zone plates incorporated in the BESSY raytracing program RAY is described. This option allows one to calculate intensity distributions in a focal plane of circular or linear zone plates considering diffraction limited resolution. Zone plate material properties are also taking into account using optical constants data tables. The complete code is available as PC-Windows version.
The intensity distributions of the coherent and partially coherent x-rays passed through a poly-capillary lens have been computed at the focal plane. The computations showed that at the appropriate experimental conditions the interference phenomenon does affect the intensity distribution. In the case of the coherent input radiation with the photon energy of 0.1 keV, the interference fringes were observed, while the non-coherent x-ray radiation produced no interference-like intensity distributions.
Neutron guides are widely used for improving the angular aperture of neutron scattering instruments in a broad band of wavelength. However, the usual guides are not effective enough in the short wavelength range. This is especially critical for time-of-flight instruments, which cannot take advantage of focusing techniques designed for steady-state monochromatic instruments. We discuss alternative ways to shape the reflecting surfaces in order to obtain a maximum angular aperture at the sample position at the expense of beam cross-section reduction. An optimal piecewise solution is proposed and Monte Carlo simulations with the IDEAS package are presented. Simulations for General Purpose Powder Diffractometer (GPPD) at Argonne National Laboratory are presented and the impact of a vertically focusing multiple-stage tapered guide is discussed. The results obtained by simulating the guide system options of engineering diffractometer VULCAN at the Spallation Neutron Source (SNS) are also presented, including vertically and horizontally tapered guide sections. The optimal multi-stage tapered guide design is discussed in terms of instrument figure of merit corresponding to different experimental needs ranging from high Q resolution to high intensity and/or high spatial resolution.
Future X-ray missions plan to utilize grazing incidence optics with very large diameter, very low angular resolutions and very light structural masses. These extremely severe requirements make the structural numerical modelling an essential tool, in order to investigate the structural integrity and the distortions of the optics, in the different scenarios on ground and on orbit.
The paper presents a ray tracing code, interfaced with general purpose finite element codes, able to predict the optical performances degradation coming from any sort of mirror distortion previously analysed by finite element approach.
By the combination of the two tools, finite element analysis and ray tracing code, it becomes possible to simulate
a very wide range of scenarios during the telescope design and optimization.
The paper shows the main features of the ray tracing code, giving some examples taken from the most recent activities
carried out for present and future X ray missions.
The Neutron Instrument Simulation Package (NISP) performs complete source-to-detector simulations of neutron instruments, including neutrons that do not follow the expected path. The original user interface (MC_Web) is a web-based application, http://strider.lansce.lanl.gov/NISP/Welcome.html. This report describes in detail the newer stand-alone Windows version, NISP_Win. Instruments are assembled from menu-selected elements, including neutron sources, collimation and transport elements, samples, analyzers, and detectors. Magnetic field regions may also be specified for the propagation of polarized neutrons including spin precession. Either interface writes a geometry file that is used as input to the Monte Carlo engine (MC_Run) in the user's computer. Both the interface and the engine rely on a subroutine library, MCLIB. The package is completely open source. New features include capillary optics, temperature dependence of Al and Be, revised source files for ISIS, and visualization of neutron trajectories at run time. Also, a single-crystal sample type has been successfully imported from McStas (with more generalized geometry), demonstrating the capability of including algorithms from other sources, and NISP_Win may render the instrument in a virtual reality file. Results are shown for two instruments under development.
We review the methods of simulating the neutron optics of three-axis spectrometers to optimize their resolution and luminosity and to interpret experimental data collected with them. The program package RESTRAX includes both a high-speed analytical (Gaussian) convolution algorithm and a Monte Carlo ray-tracing code providing enhanced accuracy in description of most of the spectrometer components. The program is designed for a fixed spectrometer layout, with emphasis on the choice of a complete set of usual neutron optical devices and on their realistic representation. The fixed layout permits to generate a highly optimized Fortran code, producing sets of 1000 - 10000 successful events per second. This speed on the turn allows for a truly interactive work when designing a new instrument or refining a model describing the scattering behavior of a sample under investigation. As an illustration, we give several examples of TAS configurations, including high-luminosity focusing arrangements and multianalyzer setups as well a demonstration of the data fitting part of RESTRAX in the case of magnetic excitations.
The software package VITESS for the simulation of neutron scattering instruments is presented. The concept, the main features and the use of the program are described. The new features of version 2.5 are explained in detail. A survey of the existing modules is given. Particular emphasis is given to modules that are used to simulate optical components, such as 'supermirror ensemble', 'monochromator/analyser' or 'bender'. Examples of simulations of existing and planned instruments are presented, e.g. a powder diffractometer installed on a long pulse target station using wavelength frame multiplication. Simulation results of the existing instrument HET at ISIS are compared to experimental results. Furthermore, a view to the coming version 2.6 is presented. One of its features is discussed in detail: It will be possible to optimize parts of the instruments numerically. As a first application, focusing guides were optimized. General results of this method as well as results for a special instrument are shown. Finally, a general outlook to the planned developments of VITESS is presented.
We present a very simple formula for calculating the total number of photons of an x-ray beam after being monochromatized by a double crystal monochromator. This is a typical case for most synchrotron radiation beamlines. The derivation of the formula and its numerical benchmarking by ray-tracing simulations are also presented.
Attaching WWW interfaces to scientific software opens new opportunities to researchers by making their results available to wide scientific community in a way complimentary to publication. We have shown that this task may be much easier than many used to think: the amount of additional code is small, the Common Gateway Interface (CGI) can be written in any language, not necessarily PERL, and the software can be interfaced on any operating system it was originally written and does not have to be ported to UNIX. This paper provides some useful recipes resulted from seven years of author's experience in developing and maintaining highly successful X-ray Web server project. All these solutions are based on free public domain software (Apache, GnuPlot, and InfoZip) and applicable for multiple computer platforms. Some practical examples are provided.
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.
The Neutron Optics Package NOP is a collection of codes for the computation of reactor spectra, neutron reflectivity of crystals, mirrors and multilayers and other quantities as cross-sections, attenuation in materials and refractive index. These calculations rely on the use of a databse of materials cross-sections and crystal structures. NOP is freely distributed as an extension of the x-ray package XOP [M. Sanchez del Rio and R.J. Dejus, SPIE proceedings 3448, 340, 1998.], from which it inherites the user interface and code structure. The NOP package can be used for estimating the reflectivity of optical elements as crystals and multilayers. The NOP output can also be used as an input for neutron instrument ray-tracing modules.
A simple genetic algorithm for global optimisation of the reflectivity of multilayer coatings in the extreme ultra-violet and X-ray wavelength ranges has been implemented as a software tool. The genetic algorithm identifies the best-performing multilayer among a population of solutions that evolves while random mutations are applied to the thickness of the layers. The tool is designed for maximising the reflectivity either over a wavelength range at fixed incident angle or over a range of incident directions at fixed energy. The algorithm has been preliminarily tested on two specific applications: a Pt/C multilayer for hard X-rays applications in astrophysics and cosmology and a Mo/Si coating prominent to next generation lithography at 13.5 nm. The results of the analyses are compared to the performances achievable with periodic multilayers and traditional supermirrors.
A suite of computer routines is presented that uses scalar wavefront theory to calculate the propagation of arbitrarily-shaped X-ray wavefronts through a series of objects and drift spaces that represent an experimental setup. The routines are coded in IDL, the Interactive Data Language, and can be included into or extended with any other IDL code. Objects and apertures in the X-ray path are modeled in the thin-object approximation, where they are represented by a two-dimensional complex transmission function. Fresnel propagation through drift spaces is carried out in Fourier space in the paraxial approximation. A variety of predefined, ready-for-use objects is included in the package. Among these are optical elements such as gratings, lenses, slits, or pinholes, as well as reference sample objects such as spheres, cylinders, test grids, etc. The materials and geometrical parameters of these objects can be freely chosen. Optical materials constants are looked up automatically in the DABAX database. The modular structure of the code makes it reasonably easy for users to add support for objects of any degree of complexity, or even other propagation schemes.
A full Monte Carlo simulation of sample scattering and the final flight path for direct geometry time-of-flight spectrometers has been developed. This allows the scattering from systems with both realistic and complex scattering geometries as well as realistic scattering functions to be modeled. This simulation, PULSCAT, interfaces with commonly available ray tracing programs, such as VITESS, that simulate the incident beam. Spectra with elastic and inelastic features resulting from scattering from isotropic scattering systems in addition to multiple scattering for amorphous scattering systems can be modeled with PULSCAT. The sample geometry used in the simulation is entered through a GUI interface. Due to the large flexibility in the input parameters for the sample, sample environment equipment can be included in the simulations allowing for scattering from ancillary equipment (such as from a standard orange cryostat) to be modeled. This makes PULSCAT a powerful tool for simulating systems and investigating spurious effects present in collected spectra.
A number of future hard X-ray (10-100 keV) telescopes will implement focusing optics with multilayer coatings. In this framework, we are developing (at INAF/Brera-Merate Astronomical Observatory) multilayer optics based on the e-beam deposition technique: this approach is suitable to coat very large surfaces at an high deposition rate; in order to test the performances of the deposited samples, X-ray reflectivity scans at the two "standard" photon energies of 8.05 and 17.4 keV are taken, returning very positive results with high peak reflectivities. However, the exact interpretation of the reflectivity curves is a complex task since it depends on a large number of parameters: the software PPM (Pythonic Program for Multilayers) has been recently developed by A. Mirone (ESRF) specifically to the aim of a friendly and fast determination of the parameters of multilayer structures. In particular, for this paper we present the layer-by-layer modelization of the characteristics (roughness, density, thickness) of multilayer stacks (Ni/C, Pt/C) by a multi-parametric "global" automatic optimization to reach the best fitting performances. In order to physically constrain the parameters, the data will be compared with the results of TEM measurements performed on the same samples, when available.