Focusing X-ray free-electron lasers (XFELs) is very important for producing ultra-intense X-ray nanoprobes. We have developed a system based on multilayer Kirkpatrick–Baez (KB) mirrors to focus XFELs to 10 nm or less at the SPring-8 Angstrom Compact free-electron LAser (SACLA) facility. The mirror optics in the system are designed with a large NA of greater than 0.01 to produce a diffraction-limited size of 6 nm at 9 keV. We constructed a precise X-ray grating interferometer based on the Talbot effect, and succeeded in fabricating near-perfect focusing mirrors with wavefront aberrations of λ/4.
However, strict error tolerances for mirror alignment can prevent sub-10 nm focusing. Errors of perpendicularity, incident angle, and astigmatism cause aberration on the focusing wavefront and characteristically change the beam shape. In particular, the required accuracy of the incident angle is 500 nrad. Due to shot-by-shot variations in the XFEL beam position and vibration of the optics, a single-shot diagnosis of beam shape is essential to align the mirrors quickly and accurately. By improving the method proposed by Sikorski et al. at the Stanford Linear Accelerator Center (SLAC), National Accelerator Laboratory, we propose a nanobeam diagnosis method based on the speckle pattern observed under coherent scattering. Computer simulation revealed that speckle size and beam size are inversely proportional. Platinum particles with a diameter of 2 nm were prepared and irradiated with X-rays to obtain a speckle pattern. Our experimental results demonstrate the successful estimation of beam shape and the alignment of all mirrors with the required accuracies.
This paper presents the designs and simulations of twin Wolter mirrors for focusing and imaging experiments with soft Xray free electron lasers. Wave-optical simulations at a photon energy of 100 eV indicate that the designed focusing Wolter mirror focuses soft X-ray beams to a 300 nm × 200 nm spot with an acceptable rotational error of 1.7 mrad × 1.4 mrad and that the objective Wolter mirror, which receives the beam that passes through the focusing Wolter mirror and a sample, forms bright-field images with a spatial resolution of 140 nm × 140 nm. The focusing Wolter mirror enables long-term experiments with high stability, and the objective Wolter mirror is applicable to imaging-before-destruction.
The absolute power of the Linac Coherent Light Source pulses has been measured accurately in the hard X-ray beamline by using simultaneously two detectors: an X-ray Gas Monitor Detector (XGMD) in tandem with a radiometer. From these measurements, we were also able to characterize and calibrate in details our sets of beamline attenuators, in addition to extending an absolute calibration for our beamline intensity monitors. Similarly, we demonstrate that commercial optical power meter has a response in the hard X-ray regime, that can be cross-correlated with the absolute power of the LCLS beam.
SACLA was inaugurated in March 2012 with two beamlines: BL3 for hard X-ray FEL and BL1 for wide range spontaneous emission. To enhance the research opportunities in soft X-ray region, the SCSS test accelerator, which was a prototype linac of SACLA and decommissioned in 2013, was upgraded, relocated to the SACLA undulator hall, and connected to BL1. The commissioning of this upgraded BL1 had been started from September in 2015, and user operation was started from June 2016. Currently, SASE-FEL pulses in the photon energy range of 20 to 150 eV are available and average pulse energy is about 70 μJ at 100 eV. We are developing beam diagnostic systems such as an arrival timing diagnostics between the SXFEL and the synchronized optical laser. We have further upgrade plans of the accelerator and the beamline. In this presentation, I will report the latest status and future upgrade plans of this beamline.
We present an optical design of a new focusing system for soft x-ray free electron lasers. The system is based on a two-staged focusing configuration that combines a Kirkpatrick-Baez focusing system with an ellipsoidal mirror so as to produce a sub-1-μm focal spot. A wave-optical simulation indicates that the power density at the focus exceeds 1018 W/cm2, which enables us to access exotic interactions between soft x-rays and matters.
This article reports the progress in the beamlines at the SPring-8 Angstrom Compact free electron LAser (SACLA). The beamline optical and diagnostics systems have been upgraded to further accelerate the scientific applications of X-ray free-electron lasers (XFELs). End-station instruments have also been developed to provide user-friendly experimental platforms which allow efficient data collection. Along with the upgrades of beamlines and experimental stations, we have established reliable and efficient procedures of the beamline operation.
KEYWORDS: Free electron lasers, X-rays, Hard x-rays, Prototyping, Extreme ultraviolet, Electron beams, Synchrotron radiation, X-ray optics, Alternate lighting of surfaces, Current controlled current source
SACLA was inaugurated in March 2012 with two beamlines: BL3 for hard X-ray FEL and BL1 for wide range spontaneous emission. Currently, all user experiments have been performed at BL3 and BL2 that was constructed as the second hard XFEL beamline. To enhance research opportunities with softer X-ray FEL, we decided to relocate the SCSS test accelerator, which was a prototype of SACLA and decommissioned in 2013, to the SACLA undulator hall, to connect to BL1, and to generate EUV and soft X-ray FEL independently of the SACLA linac.
In addition, we started commissioning of the upgraded BL1 in September 2015, and successfully observe SASE lasing at a photon energy of 36 eV in October. We are now constructing the end station, and will start commissioning in June 2016. We will install two C-band accelerator units that increase an electron beam energy up to 750 MeV with a photon energy up to 100 eV in the summer of 2016. In this presentation, I will report the latest status of the beamline.
X-ray free-electron lasers (XFELs) that utilize intense and ultra-short pulse X-rays may damage optical elements. We investigated the damage fluence thresholds of optical materials by using an XFEL focusing beam that had a power density sufficient to induce ablation phenomena. The 1 μm focusing beams with 5.5 keV and/or 10 keV photon energies were produced at the XFEL facility SACLA (SPring-8 Angstrom Compact free electron LAser). Test samples were irradiated with the focusing beams under normal and/or grazing incidence conditions. The samples were uncoated Si, synthetic silica glass (SiO2), and metal (Rh, Pt)-coated substrates, which are often used as X-ray mirror materials.
We proposed a split and delay optics setup with Si(220) crystals combined with Kirkpatric-Baez mirror optics for x-ray
pump-x-ray probe experiments at x-ray free-electron laser facilities. A prototype of the split-delay optics and its
alignment procedure were tested at BL29XUL of SPring-8. The horizontal focal profile, measured via double-beam
operation, showed good spatial overlap between the split beams with an FWHM of 100 nm, near the diffraction limit at
10 keV. High throughputs of the split-delay optics of 12% (upper) and 7.4% (lower) were obtained. The throughputs can
be improved to 30% and 20% by optimizing the upper and lower central energy, respectively.
We have developed a new method to fabricate ultrathin silicon single crystals, which can be used as spectral beam
splitters for the hard x-ray regime, based on a reactive dry etching process using plasma at atmospheric pressure. The
high crystalline perfection of the crystals was verified by both topographic and high-resolution rocking curve
measurements using coherent x-rays at the 1-km-long beamline, BL29XUL of SPring-8. The development of thin
crystals enables the construction of a split-delay unit and the provision of a dedicated branch for photon diagnostics. By
using a 20-μm-thick Si(111) crystal in the symmetric Bragg geometry as a component of a Si(111) double-crystal
monochromator, an arrival-time monitor using a destructive manner has been upgraded to a non-destructive method at
SPring-8 Angstrom Compact free-electron LAser. Using the splitting crystals in a helium atmosphere can prevent
oxidation, which can introduce a lattice distortion.
X-ray free electron lasers (XFELs) with intense and ultra-short pulse X-rays possibly induce damage to optical elements.
We investigated the damage thresholds of optical materials by using focusing XFEL beams with sufficient power density
for studying ablation phenomena. 1-μm focusing beams with 10 keV photon energy were produced at the XFEL facility
SACLA (SPring-8 Angstrom Compact free electron LAser). The focusing beams irradiated samples of rhodium-coated
substrate, which is used in X-ray mirror optics, under grazing incident condition.
With the development of hard X-ray free electron lasers, there is a pressing need to experimentally determine the single shot damage limits of presently used and potential future optical coating materials. To this end we present damage results, and analysis of fluence threshold limits, from grazing incidence geometry experiments conducted at the Spring-8 Angstrom Compact free electron LAser (SACLA) on Carbon coatings at 7 and 12 keV photon energies.
The advent of X-ray Free-electron Laser (FEL) such as the Linac Coherent Light Source (LCLS) has and will continue
to enable breakthroughs and discoveries in a wide range of scientific disciplines including physics, chemistry, structural biology, and material science. It has created high demand on user beamtime that is often left unfulfilled. We report here the fabrication, characterization and X-ray measurements of ultra-thin silicon single-crystal membranes for potentially beam-sharing the LCLS beam. Using a special fabrication process, samples of (111), (110), and (100) orientations were made with thicknesses ranging from 5 to 20 μm. Both high-resolution rocking curves and white-beam topographic data were first obtained using synchrotron X-rays, demonstrating near ideal diffraction qualities. Subsequent tests using the full LCLS FEL beam revealed lattice distortions from beam-induced membrane vibrations, which were then shown to be effectively reduced by ambient air or with smaller membrane dimensions. These findings are paving a way for a practical beam-sharing implementation at LCLS in the near future.
An inline diagnostics device was developed to measure the intrinsic shot-to-shot intensity and position fluctuations of
the SASE-based LCLS hard X-ray FEL source. The device is based on the detection of back-scattered X-rays from a
partially-transmissive thin target using a quadrant X-ray diode array. This intensity and position monitor was tested for
the first time with FEL X-rays on the XPP instrument of the LCLS. Performance analyses showed that the relative
precision for intensity measurements approached 0.1% and the position sensitivity was better than 5 μm, limited only by
the Poisson statistics of the X-rays collected in a single shot.
New physical-vapor-deposited (PVD) beryllium foils were characterized using coherent x-rays at the 1-km-long
beamline in the SPring-8. Non-uniformity in the 150 μmx150 μm area is 3% (rms) for 0.1-nm x-rays and 5% for 0.15-nm x-rays which are almost similar value to that of previous PVD foils. The PVD beryllium foil has a capability for
synchrotron radiation and x-ray free electron laser applications with spatially coherent x-rays.
For chemically amplified EUV resists, secondary electrons derived from ionization events play a critical role
in the sensitization of acid generators. In this study, we show the dependence of acid generation efficiency on
dose rate (fluence per pulse duration) by using 61 nm free-electron laser (FEL) light irradiation. The
wavelength of 61 nm (20.3 eV) is applied because single incident photon induces only single ionization event,
in contrast to the 13.4 nm EUV photon that induces 4.2 ionization events on average. The acid yield
efficiency has enhances with decreasing the dose rate. It is suggested that high density ionization enhances the
multiple spur effect.
The paper is devoted to experimental and theoretical studies of ablation of condensed matter by optical (OL),
extreme ultraviolet (EUV) and X-ray lasers (XRL). Results obtained at two different XRL are compared. The
first XRL is collision Ag-plasma laser with pulse duration τL = 7 ps and energy of quanta hv=89.3 eV, while
the second one is EUV free electron laser (EUV-FEL) and has parameters τL = 0.3 ps and energy of quanta 20.2
eV. It is shown that ablation thresholds for these XRL at LiF dielectric are approximately the same. A theory is
presented which explains slow growth of ablated mass with fluence in case of XRL as a result of transition from
spallative ablation near threshold to evaporative ablation at high fluencies. It is found that the metal irradiated
by short pulse of OL remains in elastic state even in high shear stresses. Material strength of aluminum at very
high deformation rates V/V ~ 109 s-1 is defined.
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