Papers by Lahsen Assoufid
9th Int. Particle Accelerator Conf. (IPAC'18), Vancouver, BC, Canada, 29 April-04 May 2018, Jun 1, 2018
The next generation light sources such as diffraction limited storage rings and high repetition r... more The next generation light sources such as diffraction limited storage rings and high repetition rate free electron lasers (FELs) will generate X-ray beams with significantly increased peak and average brilliance. These future facilities will require X-ray optical components capable of handling large instantaneous and average power densities while tailoring the properties of the X-ray beams for a variety of scientific experiments. In this paper we report on research and development of a single crystal diamond compound refractive lens. Diamond lenses presented here are fabricated by fs-laser cutting and subsequent polishing. Grating interferometry measurement data of these lenses had been performed at the Advanced Photon Source (Argonne). Besides the lenses, we fabricated and tested several phase correction plates, a refractive elements designed to correct for cumulative X-ray beam aberrations.
The effect of surface residual stress on the performance of high quality x-ray mirrors
Proceedings of SPIE, Sep 8, 2011
The use of high quality X-ray mirrors at synchrotron beamlines as low-energy bandpass, harmonic r... more The use of high quality X-ray mirrors at synchrotron beamlines as low-energy bandpass, harmonic rejection and high heat load optical elements has become routine. Nearly perfect optical surfaces generated on substrates and held in strain-free fixtures are of paramount importance to their success. Production of these mirrors requires extensive care, yet the effect of residual fabrication stress has not been
Journal of Synchrotron Radiation, Feb 8, 2022
Measured diffuse X-ray scattering data for a 'smooth' as well as for a 'rough' silicon sample wer... more Measured diffuse X-ray scattering data for a 'smooth' as well as for a 'rough' silicon sample were fit to theoretical expressions within the distorted wave Born approximation (DWBA). Data for the power spectral density (PSD) for both samples were also obtained by means of atomic force microscopy and optical interferometry. The Fourier transforms of trial correlation functions were fit to the PSD data and then applied to the DWBA formalism. The net correlation functions needed to fit the PSD data for each sample comprised the sum of two terms with different cutoff lengths and different self-affine fractal exponents. At zero distance these correlation functions added up to yield net values of 2 = (2) 2 and (71) 2 A ˚2 for the smooth and rough samples, respectively. X-ray scattering data were obtained at beamline 1-BM of the Advanced Photon Source. Data and fits at values of q z = 0.05 and 0.10 A ˚À1 for the smooth sample are reported. Good fits for the smooth sample were obtained at both q z values simultaneously, that is, identical fitting parameters were applied at both values of q z . The smooth sample also exhibited weak Yoneda wings and a clear distinction between the strong specular scattering and the weak diffuse scattering. Data for the rough sample were qualitatively different and exhibited very weak scattering at the specular condition in contrast to extremely large Yoneda wings. Fits for the rough sample are reported for q z = 0.04, 0.05, and 0.06 A ˚À1 . Although the large Yoneda wings could be fit quite well in both position and amplitude, scattering near the specular condition could not be equally well fit by applying the same fitting parameters at all values of q z . Albeit imperfect, best-fitting results at the specular condition were obtained by invoking only diffuse scattering, that is, without including a separate theoretical expression for specular scattering.
Proceedings of SPIE, Jan 25, 2001
An InternationalWorkshopon Metrologyfor X-rayand NeutronOptics has been held March [16][17] 2000,... more An InternationalWorkshopon Metrologyfor X-rayand NeutronOptics has been held March [16][17] 2000, at the AdvancedPhoton Source, Argonne National Laborato~near Chicago, Illinois (USA). The workshop gathered engineers and scientists from both the U.S. and around the world to evaluate metrology instrumentation and methods used to characterize surface figure and finish for long grazing incidence optics used in beamlines at synchrotrons radiation sources. This two-day workshop was motivated by the rapid evolution in the performance of x-ray and neutron sources along with requirements in optics figure and finish. More specifically, the performance of future light sources, such as free-electron laser (FEL)-based xray sources, is being pushed to new limits in term of both brilliance and coherence. As a consequence, tolerances on surface figure and finish of the next generation of optics are expected to become tighter. The timing of the workshop provided an excellent opportunity to study the problem, evaluate the state of the art in metrology instrumentation, and stimulate innovation on fiture metrology instruments and techniques to be used to characterize these optics. This paper focuses on FEL optics and metrology needs. (A more comprehensive summary of the workshop can be found elsewhere.') The performance and limitations of current metrology instrumentation will be discussed and recommendations from the workshop on Iiture metrology development to meet the FEL challenges will be detailed.
Comparison of slope and height profiles for flat synchrotron x-ray mirrors measured with a long trace profiler and a PMI Fizeau interferometer
Proceedings of SPIE, Sep 13, 2007
Long trace profilers (LTPs)(1) have been used at many synchrotron radiation laboratories worldwid... more Long trace profilers (LTPs)(1) have been used at many synchrotron radiation laboratories worldwide for over a decade to measure surface slope profiles of long grazing incidence x-ray mirrors. Phase measuring interferometers (PMIs) of the Fizeau type, on the other hand, are being used by most mirror manufacturers to accomplish the same task. However, large mirrors whose dimensions exceed the aperture of the Fizeau interferometer require measurements to be carried out at grazing incidence, and aspheric optics require the use of a null lens. While an LTP provides a direct measurement of 1D slope profiles, PMIs measure area height profiles from which the slope can be obtained by a differentiation algorithm. Measurements of the two types of instruments have been found by us to be in good agreement, but to our knowledge there is no published work directly comparing the two instruments. This paper documents that comparison. We measured two different nominally flat mirrors with both the LTP in operation at the Advanced Photon Source (a type-II LTP) and a Fizeau-type PMI interferometer (Wyko model 6000). One mirror was 500 mm long and made of Zerodur, and the other mirror was 350 mm long and made of silicon. Slope error results with these instruments agree within nearly 100% (3.11+/-0.15 murad for the LTP, and 3.11+/-0.02murad for the Fizeau PMI interferometer) for the medium quality Zerodur mirror with 3 murad rms nominal slope error. A significant difference was observed with the much higher quality silicon mirror. For the Si mirror, slope error data is 0.39+/-0.08Chirad from LTP measurements but it is 0.35 +/- 0.01 murad from PMI interferometer measurements. The standard deviations show that the Fizeau PMI interferometer has much better measurement repeatability.
Journal of Synchrotron Radiation, 2023
Adaptive X-ray mirrors are being adopted on high-coherent-flux synchrotron and X-ray free-electro... more Adaptive X-ray mirrors are being adopted on high-coherent-flux synchrotron and X-ray free-electron laser beamlines where dynamic phase control and aberration compensation are necessary to preserve wavefront quality from source to sample, yet challenging to achieve. Additional difficulties arise from the inability to continuously probe the wavefront in this context, which demands methods of control that require little to no feedback. In this work, a data-driven approach to the control of adaptive X-ray optics with piezo-bimorph actuators is demonstrated. This approach approximates the non-linear system dynamics with a discrete-time model using random mirror shapes and interferometric measurements as training data. For mirrors of this type, prior states and voltage inputs affect the shape-change trajectory, and therefore must be included in the model. Without the need for assumed physical models of the mirror's behavior, the generality of the neural network structure accommodates drift, creep and hysteresis, and enables a control algorithm that achieves shape control and stability below 2 nm RMS. Using a prototype mirror and ex situ metrology, it is shown that the accuracy of our trained model enables open-loop shape control across a diverse set of states and that the control algorithm achieves shape error magnitudes that fall within diffraction-limited performance.
Second metrology round-robin of APS, ESRF and SPring-8 laboratories of elliptical and spherical hard-x-ray mirrors
Proceedings of SPIE, Sep 13, 2007
ABSTRACT The first series of metrology round-robin measurements carried out in 2005 at the APS, E... more ABSTRACT The first series of metrology round-robin measurements carried out in 2005 at the APS, ESRF and SPring-8 metrology laboratories involving two flat x-ray mirrors and a cylindrical x-ray mirror has shown excellent agreement among the three facilities&#39; Long Trace Profilers (LTP) despite their architectural differences. Because of the growing interest in diffraction-limited hard x-ray K-B focusing mirrors, it was decided to extend the round robin measurements to spherical and aspheric x-ray mirrors. The strong surface slope variation of these mirrors presents a real challenge to LTP. As a result, new LTP measurement protocol has to be developed and implemented to ensure measurement accuracy and consistency. In this paper, different measurement techniques and procedures will be described, the results will be discussed, and comparison will be extended to micro-stitching interferometry measurements performed at Osaka University, Japan.
International workshop on metrology for x-ray and neutron optics
Synchrotron Radiation News, Nov 1, 2000
An International Workshop on Metrology for X-ray and Neutron Optics, the first of its kind, was h... more An International Workshop on Metrology for X-ray and Neutron Optics, the first of its kind, was held a t the Conference Center of the Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, USA, on March 16-17, 2000. This two-day workshop was 'attended by 64 world-class scientists and engineers from ALS/LBNL, APS/ANL, SSRL/SLAC, NASA Marshall Space Flight Center, NASA Goddard Space Flight Center, NIST, BNL, Daresbury, S N S 0 RNL, Ins t i t u t d ' 0 p t i c1 u e Orsay, Ecole de Physique et de Chimie Industrielle-Paris, LURE, BESSY, ESRF, Indian Institute of Astrophysics, Swiss Light Source, Canadian Light Source, Sincrotrone-Trieste (ELETTRA), Spring-8, IPNS/ANL, SNS/ORNL, PTB-Germany, and the Pohang Accelerator Laboratory-KOrea. Among the attendees were representatives from several companies, some of whom (Oxford Instruments, Veeco Metrology, Thermomicroscopes, SESO-France, Beamline Technologies, and Micromap) co-sponsored the events. The workshop schedule was broken into seven formal and informal sessions: four sessions on Thursday and three sessions on Friday. O n each day, formal sessions were followed by a session for informal presentations and group discussion. The purpose of the informal presentations was to provide ideas leading to a smooth transition to grou; discussion. Poster sessions were held in the APS Gallery, where vendor exhibits were located. Major topics included the performance and development of optical metrology instruments, standardization of optical components and their metrology, influence of metrology environment on measurements, mirror metrology using synchrotron radiation and comparison with optical metrology, stitching interferometry, development of simulation codes, and establishment of a working group and a Web site or a listserver for information exchange on X-ray optics and metrology and relevant issues. The workshop began with a welcome by Dennis Mills (APS/ANL) and announcements and a presentation on the status of the Advanced Photon Source (APS) operation and parameters, as well as an overview of the history of metrology for synchrotron radiation optics a t the APS. Co-chair Lahsen Assoufid gave a warm welcome to the workshop participants before beginning the first session of the workshop. The first presentation of the workshop was given by Malcolm Howells (ALS/LBNL), who reviewed the history of optics and metrology for synchrotron radiation and took a forward look a t optics and metrology needs. His presentation covered a broad range of topics including optics specifications and accuracy, material requirements, manufacturing and measuring techniques, modeling and simulation, standardization, etc. In particular, he underlined the necessity to educate synchrotron radiation optics manufacturers on the notion and use of power spectral density, and he suggested looking into the notion of performance-related specifications. Sunil Sinha (APS/ANL) presented models for surface roughness and discussed how the correlation length of the roughness interacts with the coherence length of the illuminating beam to produce diffuse scatter in one limit and speckle in the other. He compared various techniques for evaluating this important parameter, including diffuse scattering of X-rays, AFM, STM and optical profilometers. H e discussed advantages and disadvantages of each technique, as well as how they complement each other. Albert Macrander (APS/ANL) pre-
Applied Physics Letters, Nov 3, 2014
Comparison of different numerical treatments for x-ray phase tomography of soft tissue from differential phase projections
Physics in Medicine and Biology, Mar 24, 2015
X-ray imaging of soft tissue is made difficult by their low absorbance. The use of x-ray phase im... more X-ray imaging of soft tissue is made difficult by their low absorbance. The use of x-ray phase imaging and tomography can significantly enhance the detection of these tissues and several approaches have been proposed to this end. Methods such as analyzer-based imaging or grating interferometry produce differential phase projections that can be used to reconstruct the 3D distribution of the sample refractive index. We report on the quantitative comparison of three different methods to obtain x-ray phase tomography with filtered back-projection from differential phase projections in the presence of noise. The three procedures represent different numerical approaches to solve the same mathematical problem, namely phase retrieval and filtered back-projection. It is found that obtaining individual phase projections and subsequently applying a conventional filtered back-projection algorithm produces the best results for noisy experimental data, when compared with other procedures based on the Hilbert transform. The algorithms are tested on simulated phantom data with added noise and the predictions are confirmed by experimental data acquired using a grating interferometer. The experiment is performed on unstained adult zebrafish, an important model organism for biomedical studies. The method optimization described here allows resolution of weak soft tissue features, such as muscle fibers.
Test of a high-heat-load double-crystal diamond monochromator at the Advanced Photon Source
Nuclear Instruments and Methods in Physics Research, Dec 1, 1997
We have tested the first diamond double-crystal monochromator at the Advanced Photon Source (APS)... more We have tested the first diamond double-crystal monochromator at the Advanced Photon Source (APS). The monochromator consisted of two synthetic type 1b (1 1 1) diamond plates in symmetric Bragg geometry. The single-crystal plates were 6 mm × 5 mm × 0.25 mm and 6 mm × 5 mm × 0.37 mm and showed a combination of mosaic spread/strain of
Proceedings of SPIE, Dec 11, 1997
An experimental setup to measure the thermal contact conductance across a silicon-copper (Si-Cu) ... more An experimental setup to measure the thermal contact conductance across a silicon-copper (Si-Cu) interface is described, and the results obtained are presented. The resulting thermal contact resistance data are used in estimating the thermo-mechanical and optical performance of optical substrates cooled by interfaced copper cooling blocks. Several factors influence the heat transfer across solid interfaces. These include the material properties, interface pressure, flatness and roughness of the contacting surfaces, temperature, and interstitial matenal, if any. Results presented show the variation of thermal contact conductance as a function of applied interface pressure for a Cu-Si interface. Various interstitial materials investigated include iridium foil, silver foil and a liquid eutectic (Ga-In-Sn). As expected, thermal contact resistance decreases as interface pressure increases, except in the case of the eutectic, in which it was nearly constant. The softer the interstitial material, the lower the thermal contact resistance, Liquid metal provides the lowest thermal contact resistance across the Cu-Si interface, followed by the iridium foil, and then the silver foil.
Contribution a l'etude des sources ebis et a l'interaction des ions produits par ces sources avec des cibles gazeuses
La premiere partie de ce memoire est consacree a la conception de la source ebis (electron beam i... more La premiere partie de ce memoire est consacree a la conception de la source ebis (electron beam ion source) cebis ii de l'universite de cornell (usa). Dans le but de produire des ions metalliques, un systeme d'injection externe d'ions monocharges a ete realise. Ce dernier se compose d'une source annexe du type pig, d'une serie de lentilles et de deviateurs electrostatiques, d'un filtre a champ magnetique et electrique croises et d'un deviateur electrostatique a champ quadrupolaire. Les premiers tests ont montre que les ions monocharges sont bien introduits et ionises dans cebis ii. Cependant le deroulement de l'injection a ete fortement gene par la diffusion du gaz de la decharge de la source pig dans la ligne de faisceau et dans la source cebis ii. La deuxieme partie porte que l'etude experimentale du processus d'echange de charge a basse vitesse (v=0,4 u. A. ) entre des faisceaux d'ions ar17+ et des cibles gazeuses. Dans un premier temps nous avons observe a l'aide d'un detecteur sili les rayons x emis lors de l'interaction de ces faisceaux avec des cibles h puis h2. Le but de cette experience est de comparer directement le transfert de moments angulaires de la simple et de la double capture. Les spectres obtenus ont montre que pour les deux processus la capture a lieu dans des etats de grands moments angulaires. Ensuite, nous avons etudie, a l'aide d'un spectrographe a haute resolution (cristal ce111 courbe) les rayons x emis lors de la collision de ces memes faisceaux avec des cibles he, h, h2 et n. Les resultats obtenus ont montre que les processus de capture double non suivie d'autoionisation ont une probabilite importance
A novel X-ray beam monitoring and wavelength calibration using four-beam diffraction: theory and experiments (Conference Presentation)
Journal of Synchrotron Radiation, Feb 4, 2015
A method to pre-shape mirror substrates through etching with a broad-beam ion source and a contou... more A method to pre-shape mirror substrates through etching with a broad-beam ion source and a contoured mask is presented. A 100 mm-long elliptical cylinder substrate was obtained from a super-polished flat Si substrate with a 48 nm rootmean-square (r.m.s.) figure error and a 1.5 A ˚r.m.s. roughness after one profileetching process at a beam voltage of 600 V without iteration. A follow-up profile coating can be used to achieve a final mirror. Profile etching and profile coating combined provide an economic way to make X-ray optics, such as nested Kirkpatrick-Baez mirrors.
Wavelet-transform-based speckle vector tracking method for X-ray phase imaging
Optics Express, Oct 19, 2020
We introduce a new X-ray speckle-vector tracking method for phase imaging, which is based on the ... more We introduce a new X-ray speckle-vector tracking method for phase imaging, which is based on the wavelet transform. Theoretical and experimental results show that this method, which is called wavelet-transform-based speckle-vector tracking (WSVT), has stronger noise robustness and higher efficiency compared with the cross-correlation-based method. In addition, the WSVT method has the controllable noise reduction and can be applied with fewer scan steps. These unique features make the WSVT method suitable for measurements of large image sizes and phase shifts, possibly under low-flux conditions, and has the potential to broaden the applications of speckle tracking to new areas requiring faster phase imaging and real-time wavefront sensing, diagnostics, and characterization.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Dec 11, 2018
Journal of Synchrotron Radiation, 2022
Rigorous dynamical theory calculations show that four-beam diffraction (4BD) can be activated onl... more Rigorous dynamical theory calculations show that four-beam diffraction (4BD) can be activated only by a unique photon energy and a unique incidence direction. Thus, 4BD may be used to precisely calibrate X-ray photon energies and beam positions. Based on the principles that the forbidden-reflection 4BD pattern, which is typically an X-shaped cross, can be generated by instant imaging using the divergent beam from a point source without rocking the crystal, a detailed real-time high-resolution beam (and source) position monitoring scheme is illustrated for monitoring two-dimensional beam positions and directions of modern synchrotron light sources, X-ray free-electron lasers and nano-focused X-ray sources.
Status of the diamond CRL development
Advances in X-Ray/EUV Optics and Components XIV, 2019
The next generation light sources such as diffraction-limited storage rings and high repetition r... more The next generation light sources such as diffraction-limited storage rings and high repetition rate free electron lasers (FELs) will generate x-ray beams with significantly increased peak and average brilliance. These future facilities will require x-ray optical components capable of handling large instantaneous and average power densities while tailoring the properties of the x-ray beams for a variety of scientific experiments. We have been developing diamond x-ray refractive lens for 3 years. Standard deviation of lens residual gradually was decreased to sub-micron values. Post-ablation polishing procedure yields 10-20nm surface roughness, Ra. In this paper we report on recent developments towards beam-line ready optic.
Advances in X-Ray/EUV Optics and Components XIII, 2018
We describe design guidelines for soft x-ray wavefront sensors and experimentally demonstrate the... more We describe design guidelines for soft x-ray wavefront sensors and experimentally demonstrate their performance, comparing grating-based lateral shearing interferometry and Hartmann wavefront sensing. We created a compact shearing interferometer concept with a dense array of binary amplitude gratings in a single membrane to support one-dimensional wavefront measurements across a wide wavelength range without the need for longitudinal position adjustment. We find that a common scaling parameter based on wavelength and the distance to the measurement plane guides the design of both systems toward optimal sensitivity. We show preliminary results from recent experiments demonstrating one and two-dimensional wavefront sensing below the Maréchal criterion.
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Papers by Lahsen Assoufid