Alexey Suvorov

Performance of a collimating L-shaped laterally graded multilayer mirror for the IXS analyzer system at NSLS-II.

The L-shaped laterally graded multilayer mirror is a vital part of the ultrahigh-energy and momentum-resolution inelastic X-ray scattering spectrometer at the National Synchrotron Light Source II. This mirror was designed and implemented as a two-dimensional collimating optic for the analyzer system. Its performance was characterized using a secondary large-divergence source at the 30-ID beamline of the Advanced Photon Source, which yielded an integrated reflectivity of 47% and a collimated beam divergence of 78 µrad with a source size of 10 µm. Numerical simulations of the mirror performance in tandem with the analyzer crystal optics provided details on the acceptance sample volume in forward scattering and defined the technical requirements on the mirror stability and positioning precision. It was shown that the mirror spatial and angular stability must be in the range <8.4 µm and <21.4 µrad, respectively, for reliable operation of the analyzer.

Emergent Optical Phononic Modes upon Nanoscale Mesogenic Phase Transitions

The investigation of phononic collective excitations in soft matter systems at the molecular scale has always been challenging due to limitations of experimental techniques in resolving low-energy modes. Recent advances in inelastic X-ray scattering (IXS) enabled the study of such systems with unprecedented spectral contrast at meV excitation energies. In particular, it has become possible to shed light on the low-energy collective motions in materials whose morphology and phase behavior can easily be manipulated, such as mesogenic systems. The understanding of collective mode behavior with a Q-dependence is the key to implement heat management based on the control of a sample structure. The latter has great potential for a large number of energy-inspired innovations. As a first step toward this goal, we carried out high contrast IXS measurements on a liquid crystal sample, D7AOB, which exhibits solid-like dynamic features, such as the coexistence of longitudinal and transverse phononic modes. For the first time, we found that these terahertz phononic excitations persist in the crystal, smectic A, and isotropic phases. Furthermore, the intermediate smectic A phase is shown to support a van der Waals-mediated nonhydrodynamic mode with an optical-like phononic behavior. The tunability of the collective excitations at nanometer-terahertz scales via selection of the sample mesogenic phase represents a new opportunity to manipulate optomechanical properties of soft metamaterials.

Partially-coherent wavefront propagation simulations for inelastic X-ray scattering beamline including crystal optics

Up to now simulation of perfect crystal optics in the “Synchrotron Radiation Workshop” (SRW) wave-optics computer code was not available, thus hindering the accurate modelling of synchrotron radiation beamlines containing optical components with multiple-crystal arrangements, such as double-crystal monochromators and high-energy-resolution monochromators. A new module has been developed for SRW for calculating dynamical diffraction from a perfect crystal in the Bragg case. We demonstrate its successful application to the modelling of partially-coherent undulator radiation propagating through the Inelastic X-ray Scattering (IXS) beamline of the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory. The IXS beamline contains a double-crystal and a multiple-crystal highenergy- resolution monochromator, as well as complex optics such as compound refractive lenses and Kirkpatrick-Baez mirrors for the X-ray beam transport and shaping, which makes it an excellent case for benchmarking the new functionalities of the updated SRW codes. As a photon-hungry experimental technique, this case study for the IXS beamline is particularly valuable as it provides an accurate evaluation of the photon flux at the sample position, using the most advanced simulation methods and taking into account parameters of the electron beam, details of undulator source, and the crystal optics.

Theory and numerical simulations of x-ray nanofocusing by bent crystal in back diffraction geometry

A point-to-point x-ray focusing of a spherical wave by means of cylindrically bent crystal in symmetric Bragg back diffraction geometry was investigated theoretically and simulated numerically. To separate the focal plane from an incident x-ray beam, a thin flat crystal was introduced into the setup. The effect of flat crystal diffraction on the focusing performance of the double crystal setup is discussed. It is shown that the aberration free focusing can be achieved with aspherical surface shape of the strongly bent crystal. A correction term for the surface displacement function free from spherical aberrations is derived. Thorough numerical simulations demonstrated agreement with the theoretical analysis and excellent focusing performance of 2.4 nm. Theoretically, the demonstrated result can be further improved almost by an order of magnitude.

Initial performances of first undulator-based hard x-ray beamlines of NSLS-II compared to simulations

Commissioning of the first X-ray beamlines of NSLS-II included detailed measurements of spectral and spatial distributions of the radiation at different locations of the beamlines, from front-ends to sample positions. Comparison of some of these measurement results with high-accuracy calculations of synchrotron (undulator) emission and wavefront propagation through X-ray transport optics, performed using SRW code, is presented.

Dynamical modeling of high-energy-resolution x-ray optics

Theoretical analysis of high-energy-resolution x-ray optics, such as backscattering and four-bounce monochromators and analyzers, has been carried out using computer modeling within the framework of the dynamical theory of x-ray diffraction. This analysis identifies several important techniques for the precise alignment and determination of the energy and bandwidth of the monochromators. The destructive contribution of multiple-wave diffraction to the scattering intensity of x-ray backscattering optics has also been analyzed in details. An important method has been identified which allows this destructive contribution to be avoided.

Simulation of an IXS imaging analyzer with an extended scattering source

A concept of an inelastic x-ray scattering (IXS) spectrograph with an imaging analyzer was proposed recently and discussed in a number of publications (see e.g. Ref.1). The imaging analyzer as proposed combines x-ray lenses with highly dispersive crystal optics. It allows conversion of the x-ray energy spectrum into a spatial image with very high energy resolution. However, the presented theoretical analysis of the spectrograph did not take into account details of the scattered radiation source, i.e. sample, and its impact on the spectrograph performance. Using numerical simulations we investigated the influence of the finite sample thickness, the scattering angle and the incident energy detuning on the analyzer image and the ultimate resolution.

Simulation of the ultrahigh energy resolution IXS analyzer system at NSLS-II

The ultrahigh energy resolution IXS spectrometer being developed at the National Synchrotron Light Source II (NSLSII) employs an innovative optical design. Its analyzer system utilizes an L-shaped laterally graded multilayer mirror in tandem with a multi-crystal arrangement. The multi-crystal arrangement explores the angular dispersion effect in extremely asymmetric Bragg reflections to achieve sub-meV energy resolution at an energy about 9.1 keV. Its angular acceptance (~ 0.1 mrad) is about two orders of magnitude lower than the spherically-bent backscattering analyzers conventionally used in other IXS spectrometers. The L-shaped laterally graded multiplayer mirror was designed to increase the angular acceptance of this new multi-crystal optics to a comparable level. It performs angular collimation of the incoming beam from about 15 mrad down to 0.1 mrad in both vertical and horizontal directions. Here we present simulations of the mirror performance and study the positioning and stability requirements in conjunction with the multicrystal energy analyzer.

NANO FABRICATION OF COMPOUND BIFOCAL ZONE PLATE FOR X-RAY OPTICS

The development of nanotechnology gives new possibilities for fabrication of different x-ray optical elements. We present results of focusing properties the compound silicon linear Zone Plate (ZP) for first and second orders. The compound silicon linear ZP is fabricated by an electron beam lithography and lift-off technology. ZPs structures have been etched by ion-plasma up to 6μm deep. A linear ZP of the first and second orders fabricated for x-ray radiation 10kev energy, the focal distance is 57sm. The entire aperture is 357.64μm, the width of the outermost zones of the first and second orders are 595nm, and the number of the first and second order zones are: N(1) + N(2) = 251.The experiment was performed at the beam line BL29XU Spring-8 of the Japan Synchrotron Radiation Facility. The experimentally and theoretically investigations were done for x-ray energy at the 10keV and 12.4keV (0.1nm wavelength). The radial distribution of intensity is determined as a convolution of the zone plate transmission function and the Kirchhoff propagator in par-axial approximation. The algorithm is based on the FFT procedure and studied by means of computer programming simulation.