Choji Saji

Bio: Choji Saji is an academic researcher. The author has contributed to research in topics: SACLA & Data acquisition. The author has an hindex of 3, co-authored 9 publications receiving 1331 citations.

A compact X-ray free-electron laser emitting in the sub-ångström region

Abstract: Researchers report sub-angstrom fundamental-wavelength lasing at the SPring-8 Angstrom Compact Free-Electron Laser in Japan. The output has a maximum power of more than 10 GW, a pulse duration of 10−14 s and a lasing wavelength of 0.634 A.

Evaluation of data-acquisition front ends for handling high-bandwidth data from X-ray 2D detectors: A feasibility study

Abstract: Two-dimensional (2D) X-ray detectors are indispensable for synchrotron radiation and X-ray free-electron laser experiments, such as coherent X-ray imaging, spectroscopy, and time-resolved experiments. In these experiments, special, temporal, or photon-energy information is projected onto the surface of a 2D X-ray detector, and it is generally accepted that detectors with a larger number of pixels and a higher dynamic range will provide better information on the sample. An example of a high-performance application in this area is SOPHIAS (Silicon-On-Insulator Photon Imaging Array Sensor), which is a next generation detector under development at the SPring-8 facility, Japan. Since such systems demand a high-bandwidth front end for data acquisition (DAQ), a prototype front end for SOPHIAS is also under development. Here, we have performed a feasibility study of the prototype front end using an evaluation board, which consists of an FPGA (field-programmable gate array) with an FMC (FPGA mezzanine card) interface to support various physical layers of sensor readout modules and back-end DAQ. The bandwidths were measured for various combinations of protocols and physical layers. In many photon science applications, scalability from a single module to many modules is important, so a compact desktop-type DAQ system was also evaluated. Measurements of the bandwidth using the evaluation board indicated that an effective bandwidth of 9 Gbps and 16 Gbps was achieved using SFP+ (Small Form-factor Pluggable Plus) with XAUI (X (ten) Attached Unit Interface) and PCI Express (Peripheral Component Interconnect Express), respectively.

First operation of the SACLA control system in spring-8

Abstract: The control system design for the X-ray free electron laser facility (SACLA, SPring-8 Angstrom Compact free electron LAser) in SPring-8 has started in 2006. The facility construction started in 2006 and has completed to begin the electron beam commissioning in March 2011. The electron beams were successfully accelerated up to 8GeV and the first SASE X-ray was observed at the beginning of June. The control system is built by using MADOCA control framework that was developed in SPring-8. The upper control layer consists of Linux PCs for operator consoles, Sybase RDBMS for data management and NAS for NFS. The lower layer consists of VMEbus systems with off-the-shelf I/O boards and specially developed boards for RF waveform processing with high precision. Solaris OS is adopted to operate VMEbus CPU. The PLC is used for slow control and connected to the VME systems via FL-net. The Devicenet is adopted for the frontend device control to reduce the number of signal cables. The control system started operation in advance to support beam tuning. The reliability of the control system was enough during the commissioning but small system tuning and adjustment was necessary to achieve more stability.

Upgrade of accelerator radiation safety system for spring-8

Abstract: An accelerator radiation safety system (accelerator safety interlock system) that protects users from radiation hazards induced by electron beams and synchrotron radiation has been operating for over a decade at SPring8. The working of the accelerator safety interlock system for SPring-8 is based on the operation mode control system. The working of the latter system became complicated because the number of “operation modes” increased over time in accordance with SPring-8 upgrades. Therefore, we are planning to construct a new accelerator safety interlock system. Here, we report the status of the current safety interlock system and the conceptual design of the new one. This upgrade is scheduled for the summer of 2010.

System design of accelerator safety interlock for the xfel/spring-8

Abstract: The accelerator safety interlock system (ASIS) for XFEL/SPring-8 protects personnel from radiation hazards. The ASIS consists of three independent systems: central, emergency, and beam-route interlocks. If the ASIS detects an unsafe status, it turns off the permission signal for accelerator operation, thereby stopping the electron beams. The delay time for the permission signal propagation must be less than 16.6 ms. Furthermore, reliability and stability of the personnel protection system are indispensable. Therefore, we have used programmable logic controllers for stability and developed optical modules for fast signal transmission. In this paper, we describe the system design of the ASIS.

Phase Retrieval with Application to Optical Imaging: A contemporary overview

Abstract: i»?The problem of phase retrieval, i.e., the recovery of a function given the magnitude of its Fourier transform, arises in various fields of science and engineering, including electron microscopy, crystallography, astronomy, and optical imaging. Exploring phase retrieval in optical settings, specifically when the light originates from a laser, is natural since optical detection devices [e.g., charge-coupled device (CCD) cameras, photosensitive films, and the human eye] cannot measure the phase of a light wave. This is because, generally, optical measurement devices that rely on converting photons to electrons (current) do not allow for direct recording of the phase: the electromagnetic field oscillates at rates of ~1015 Hz, which no electronic measurement device can follow. Indeed, optical measurement/detection systems measure the photon flux, which is proportional to the magnitude squared of the field, not the phase. Consequently, measuring the phase of optical waves (electromagnetic fields oscillating at 1015 Hz and higher) involves additional complexity, typically by requiring interference with another known field, in the process of holography.

Highly coherent and stable pulses from the FERMI seeded free-electron laser in the extreme ultraviolet

Abstract: Researchers demonstrate the FERMI free-electron laser operating in the high-gain harmonic generation regime, allowing high stability, transverse and longitudinal coherence and polarization control.

X-Rays and Extreme Ultraviolet Radiation: Principles and Applications

Abstract: This self-contained, comprehensive book describes the fundamental properties of soft x-rays and extreme ultraviolet (EUV) radiation and discusses their applications in a wide variety of fields, including EUV lithography for semiconductor chip manufacture and soft x-ray biomicroscopy. The author begins by presenting the relevant basic principles such as radiation and scattering, wave propagation, diffraction, and coherence. He then goes on to examine a broad range of phenomena and applications. The topics covered include EUV lithography, biomicroscopy, spectromicroscopy, EUV astronomy, synchrotron radiation, and soft x-ray lasers. He also provides a great deal of useful reference material such as electron binding energies, characteristic emission lines and photo-absorption cross-sections. The book will be of great interest to graduate students and researchers in engineering, physics, chemistry, and the life sciences. It will also appeal to practicing engineers involved in semiconductor fabrication and materials science.

DIALS: implementation and evaluation of a new integration package

Abstract: The DIALS project is a collaboration between Diamond Light Source, Lawrence Berkeley National Laboratory and CCP4 to develop a new software suite for the analysis of crystallographic X-ray diffraction data, initially encompassing spot finding, indexing, refinement and integration. The design, core algorithms and structure of the software are introduced, alongside results from the analysis of data from biological and chemical crystallography experiments.

Femtosecond x rays from laser-plasma accelerators

Abstract: Relativistic interaction of short-pulse lasers with underdense plasmas has recently led to the emergence of a novel generation of femtosecond x-ray sources. Based on radiation from electrons accelerated in plasma, these sources have the common properties to be compact and to deliver collimated, incoherent, and femtosecond radiation. In this article, within a unified formalism, the betatron radiation of trapped and accelerated electrons in the so-called bubble regime, the synchrotron radiation of laser-accelerated electrons in usual meter-scale undulators, the nonlinear Thomson scattering from relativistic electrons oscillating in an intense laser field, and the Thomson backscattered radiation of a laser beam by laser-accelerated electrons are reviewed. The underlying physics is presented using ideal models, the relevant parameters are defined, and analytical expressions providing the features of the sources are given. Numerical simulations and a summary of recent experimental results on the different mechanisms are also presented. Each section ends with the foreseen development of each scheme. Finally, one of the most promising applications of laser-plasma accelerators is discussed: the realization of a compact free-electron laser in the x-ray range of the spectrum. In the conclusion, the relevant parameters characterizing each sources are summarized. Considering typical laser-plasma interaction parameters obtained with currently available lasers, examples of the source features are given. The sources are then compared to each other in order to define their field of applications.