Note: Spatial resolution of Fuji BAS-TR and BAS-SR imaging plates

The spatial resolution of two types of imaging plates, Fuji BAS-TR and Fuji BAS-SR, has been measured using a knife-edge x-ray source of 8-keV Cu K(α) radiation. The values for the spatial resolution, defined as the distance between 10% and 90% levels of the edge spread function, are 94 μm and 109 μm, respectively. The resolution values are important for quantitative analysis of x-ray and particle imaging and spectroscopic diagnostics.     

Single-shot beam-position monitor for x-ray free electron laser

We have developed an x-ray beam-position monitor for detecting the radiation properties of an x-ray free electron laser (FEL). It is composed of four PIN photodiodes that detect backscattered x-rays from a semitransparent diamond film placed in the beam path. The signal intensities from the photodiodes are used to compute the beam intensity and position. A proof-of-principle experiment at a synchrotron light source revealed that the error in the beam position is reduced to below 7 μm by using a nanocrystal diamond film prepared by plasma-enhanced chemical vapor deposition. Owing to high dose tolerance and transparency of the diamond film, the monitor is suitable for routine diagnostics of extremely intense x-ray pulses from the FEL.     

Scanning X-ray radiography with an improved detection scheme

A scanning X-ray microscope based on scannable electron gun is described. In spite of its extremely simple conception (classical X-ray source and no requirement for X-ray optics), it gave good images in about 10–20 min. To check the imaging properties of this system, an integrated circuit was used as a sample; the resulting images show that the resolution is about 6 to 7 μm. This result is discussed, and possible further developments are pointed out. Improvements to bring the theoretical resolution limit to a few tenths of a micrometer are also suggested.     

Evaluation of a Linear Self-Scanned Photodiode Array Detector for Direct Detection of 6-8 Kev X-Rays

ABSTRACT

The performance of a commercially available 1-dimensional x-ray detector based on a directly bombarded self-scanned photo-diode array has been evaluated for x-rays in the 6-8 KeV range. The detector consists of a linear array of 1024 pixels, each approximately 25 μm wide by 2000 μm tall. Modifications to allow cooling to -55°C, which is required for long x-ray exposures, are described. The signal yield is 0.63 ADC counts/Fe⁵⁵ x-ray, resulting in a detective quantum efficiency greater than 0.5 for doses over a range of 10 to 10⁴ x-rays per pixel per scan when operated at -55°C. The resolution is about 3 pixels (75 μm FWHM) and the response with respect to dose is linear up to 1.5 x 10⁴ x-rays integrated per pixel per scan. There is some non-linearity at doses below about 1000 x-rays/pixel/scan. The detector has very little geometric distortion. The uncorrected uniformity of response of the individual pixels (field flatness) is good to about 2%. However, the variation in responsiveness is stable and a field flatness calibration can be readily used to correct the uniformity of response.     

Compact x-ray microradiograph for in situ imaging of solidification processes: bringing in situ x-ray micro-imaging from the synchrotron to the laboratory

A laboratory based high resolution x-ray radiograph was developed for the investigation of solidification dynamics in alloys. It is based on a low-power microfocus x-ray tube and is potentially appropriate for x-ray diagnostics in space. The x-ray microscope offers a high spatial resolution down to approximately 5 μm. Dynamic processes can be resolved with a frequency of up to 6 Hz. In reference experiments, the setup was optimized to yield a high contrast for AlCu-alloys. With samples of about 150 μm thickness, high quality image sequences of the solidification process were obtained with high resolution in time and space.     

Time-resolved near-edge x-ray absorption fine structure spectroscopy on photo-induced phase transitions using a tabletop soft-x-ray spectrometer

We present a table-top soft-x-ray spectrometer for the wavelength range λ = 1-5 nm based on a stable laser-driven x-ray source, making use of a gas-puff target. With this setup, optical light-pump/soft-x-ray probe near-edge x-ray absorption fine structure (NEXAFS) experiments with a temporal resolution of about 230 ps are feasible. Pump-probe NEXAFS measurements were carried out in the "water-window" region (2.28 nm-4.36 nm) on the manganite Pr(0.7)Ca(0.3)MnO(3), investigating diminutive changes of the oxygen K edge that derive from an optically induced phase transition. The results show the practicability of the table-top soft-x-ray spectrometer on demanding investigations so far exclusively conducted at synchrotron radiation sources.     

Spectroscopy of betatron radiation emitted from laser-produced wakefield accelerated electrons

X-ray betatron radiation is produced by oscillations of electrons in the intense focusing field of a laser-plasma accelerator. These hard x-rays show promise for use in femtosecond-scale time-resolved radiography of ultrafast processes. However, the spectral characteristics of betatron radiation have only been inferred from filter pack measurements. In order to achieve higher resolution spectral information about the betatron emission, we used an x-ray charge-coupled device to record the spectrum of betatron radiation, with a full width at half maximum resolution of 225 eV. In addition, we have recorded simultaneous electron and x-ray spectra along with x-ray images that allow for a determination of the betatron emission source size, as well as differences in the x-ray spectra as a function of the energy spectrum of accelerated electrons.     

Grazing incidence extreme ultraviolet spectrometer fielded with time resolution in a hostile z-pinch environment

This recently developed diagnostic was designed to allow for time-gated spectroscopic study of the EUV radiation (4 nm < λ < 15 nm) present during harsh wire array z-pinch implosions. The spectrometer utilizes a 25 μm slit, an array of 3 spherical blazed gratings at grazing incidence, and a microchannel plate (MCP) detector placed in an off-Rowland position. Each grating is positioned such that its diffracted radiation is cast over two of the six total independently timed frames of the MCP. The off-Rowland configuration allows for a much greater spectral density on the imaging plate but only focuses at one wavelength per grating. The focal wavelengths are chosen for their diagnostic significance. Testing was conducted at the Zebra pulsed-power generator (1 MA, 100 ns risetime) at the University of Nevada, Reno on a series of wire array z-pinch loads. Within this harsh z-pinch environment, radiation yields routinely exceed 20 kJ in the EUV and soft x-ray. There are also strong mechanical shocks, high velocity debris, sudden vacuum changes during operation, energic ion beams, and hard x-ray radiation in excess of 50 keV. The spectra obtained from the precursor plasma of an Al double planar wire array contained lines of Al IX and AlX ions indicating a temperature near 60 eV during precursor formation. Detailed results will be presented showing the fielding specifications and the techniques used to extract important plasma parameters using this spectrometer.     

Properties of frozen sections relevant to quantitative microanalysis

Difficulties in the quantitative X-ray microanalysis of frozen sections may conceivably arise from ice-crystal damage and from electron-beam damage. X-ray peak-to-continuum ratios are commonly taken as a quantitative index of elemental concentrations. But recent reports suggest that in dehydrated frozen sections such ratios vary greatly with the scale of ice-crystal formation existing prior to sublimation. The experiments in these reports are re-interpreted here; it is argued that peak intensities may be affected by ice-crystal scale but that ratios of peak to continuum should not be affected after corrections for exogenous continuum. The accuracy of the peak-to-continuum method is affected by beam-induced loss of mass from microvolumes during analysis. Mass loss can be reduced or slowed by a cold-stage. For example, the radiation sensitivity for loss of chlorine from PVC is reduced by a factor of 1000 or more with reduction of temperature from 300 to 100 K. For sections of soft tissue the effectiveness of cooling is not nearly so striking but at 100 K, analyses of 1 μm frozen-hydrated sections by the continuum method, with spatial resolution of the order of 1 μm, can be completed before substantial mass loss occurs. However, analysis of frozen-hydrated sections by the continuum method at much higher resolution, say 100 nm resolution in 100 nm sections, is precluded by mass loss. Measurements of local mass can be achieved with much lower dose by observation and calibration of the electron transmission or backscattering. But even with these methods, several problems remain in achieving quantitative X-ray analysis at very high resolution.     

Laser pulse-induced transitions on surfaces of bulk material,traced by thermal and secondary electrons

Thermal and electron beam-released electrons were exploited to probe the dynamics of surface modifications, induced by a Q-switched frequency-doubled Nd:YAG laser within areas of 100 μm Φ on bulk silicon and metals. Changes of surface geometry and phase transitions show up as pronounced peaks and steps in the emitted electron currents. They occur within Φ 200 ns after the laser pulse and consume times from less than 5 ns up to 200 ns. Applications of pulsed radiation power for surface machining, recrystallization and vitrification or for production of microstructures on bulk substrates for integrated devices are continually extending (Bäuerle 1984). Laser pulses are most frequently used, in spite of their inhomogeneous absorption, as contrasted to electron and ion beams, because of easy handling of power and no need for vacuum in many cases. The diagnostic methods usually applied to probe the dynamics of pulse-induced transitions are still those introduced at the beginning of the “laser annealing” technique, exploiting light reflection and transmission, and to a minor extent x-ray and electron diffraction, mass spectrometry and electrical conductivity (Khaibullin 1984, Larson 1984). Naturally, each diagnostic tool has a restricted range of useful application, so further methods combining high temporal and spatial resolution and equally applicable to semiconductors and metals are highly desirable. Thermal and secondary electrons are expected to be susceptible to changes of temperature and geometry of a surface, occuring during laser pulse machining. In fact, photon-assisted thermal electron emission was used to probe thermal relaxations in laser-pulsed semiconductors (Leung and van Driel 1984), however, the thermal electrons were not used to trace geometric modifications. Furthermore, secondary electrons have not yet been tested as a probe for very fast single effects. This report describes first results, demonstrating the usability of emitted electrons as a probe for nanosecond transitions on surfaces of bulk material. An electron optical equipment was built, consisting of electron gun, condensor lens and specimen chamber, allowing synchronized laser and electron beam pulsing of the specimen. Its surface was probed by the photo-thermally emitted electrons and ions or by the secondary and backscattered electrons, which were generated by the focussed primary electron beam. The latter was pulsed in order to suppress electron radiation damage. For laser treatment a pulse of a Q-switched frequency-doubled Nd:YAG laser (FWHM 20 ns) was focussed with a lens and a dielectric mirror onto the specimen, which could be viewed with a microscope for aligning the laser and the primary electron beam. Both beams had a diameter of 100 μm (FWHM) on the specimen. The emitted charges were collected by a shielded scintillator/multiplier detector of the Everhart-Thornley type, having a rise time of = 3 ns and being protected against excessive green laser light by an edge filter. Despite the simp1e set-up, rapid changes of the surface by vaporization, melting, solidification could readily be observed within areas down to 30 μm Φ on the nanosecond time scale. Flow and disrupture of liquid layers occur after the laser pulse, delayed by several 10 ns (Figs. 1 and 2). The dispersion of metal liquids by temperature-induced gradients of the surface tension may consume times from below 5 ns (Fig. 2a) up to 200 ns (Fig. la). It is signalized by a large increase of electron emission, probably due to Schottky effect at charged transient tips within the disintegrating liquid. First order phase transitions involving latent heats are readily indicated by thermal electrons. Solidification of a melt, for instance, shows up in the emission current as a prolonged plateau with an abrupt drop within 20 … 40 ns (Fig. 3). Summarizing, secondary and thermal electrons are well suited to trace single transitions on the surface of bulk material on the nanosecond-micrometer scale. In contrast to other diagnostic probes the spatial resolution may be increased well below 1 μm by improved focussing of the primary electron beam.     

High resolution far-infrared Fourier transform spectroscopy of radicals at the AILES beamline of SOLEIL synchrotron facility

Experimental far-infrared (FIR) spectroscopy of transient species (unstable molecules, free radicals, and ions) has been limited so far in both emission and absorption (mainly by the low probability of spontaneous emission in that spectral range and the low brightness of continuum sources used for absorption measurements, respectively). Nevertheless, the FIR spectral range recently became of high astrophysical relevance thanks to several new observational platforms (HERSCHEL, ALMA...) dedicated to the study of this region suitable for the detection of the emission from cold objects of the interstellar medium. In order to complete the experimental dataset concerning transient species, three discharge experiments dedicated to the recording of high resolution FIR spectra of radicals have been developed at the Advanced Infrared Line Exploited for Spectroscopy (AILES) which extracts the bright FIR synchrotron continuum of the synchrotron facility SOLEIL. These experiments make use of a high resolution (R = 0.001 cm(-1)) Bruker IFS125 Fourier transform (FT) spectrometer. An emission setup (allowing to record spectra of radicals excited at high rotational and vibrational temperatures) and two absorption setups (exploiting the bright synchrotron source at the highest resolution available on the FT) are alternatively connected to the FT. The advantages and limitations of these techniques are discussed on the basis of the recent results obtained on OH and CH radicals. These results constitute the first FIR spectra of radicals using synchrotron radiation, and the first FIR spectrum of a C-bearing radical using FT-spectroscopy.     

Hard x-ray transmission crystal spectrometer at the OMEGA-EP laser facility

The transmission crystal spectrometer (TCS) is approved for taking data at the OMEGA-EP laser facility since 2009 and will be available for the OMEGA target chamber in 2010. TCS utilizes a Cauchois type cylindrically bent transmission crystal geometry with a source to crystal distance of 600 mm. Spectral images are recorded by image plates in four positions, one IP on the Rowland circle and three others at 200, 400, and 600 mm beyond the Rowland circle. An earlier version of TCS was used at LULI on experiments that determined the x-ray source size from spectral line broadening on one IP positioned behind the Rowland circle. TCS has recorded numerous backlighter spectra at EP for point projection radiography and for source size measurements. Hard x-ray source size can be determined from the source broadening of both K shell emission lines and from K absorption edges in the bremsstrahlung continuum, the latter being a new way to measure the spatial extent of the hard x-ray bremsstrahlung continuum.     

Multichannel linear detector for x-ray spectroscopy

This paper considers a new linear multichannel x-ray detector designed on the basis of a BLPP-369M4 silicon photodiode array (2612 photodiodes, array pitch 12.5 µm, height 4 mm, and dynamic range 10⁴). The structure and characteristics of the multichannel detector are given, along with the Kα1,2, Kβ ₁, and Kβ ₅ x-ray emission lines and a K-edge absorption spectrum of metallic copper recorded on a universal URS-2I spectrometer using this detector. The resolution and the signal/noise ratio of these spectra are superior to those of spectra recorded by an SRPP-21 gas ionization counter at the same recording time. The detector has a spatial resolution of 20 µm and an x-ray detection limit to equal 1 quantum at λ = 1.54 Å. It is suitable for studying the fine structure of absorption spectra at 1–10 Å.     

KMC-1: a high resolution and high flux soft x-ray beamline at BESSY

The crystal monochromator beamline KMC-1 at a BESSY II bending magnet covers the energy range from soft (1.7 keV) to hard x-rays (12 keV) employing the (n,-n) double crystal arrangement with constant beam offset. The monochromator is equipped with three sets of crystals, InSb, Si (111), and Si (422) which are exchangeable in situ within a few minutes. Beamline and monochromator have been optimized for high flux and high resolution. This could be achieved by (1) a windowless setup under ultrahigh-vacuum conditions up to the experiment, (2) by the use of only three optical elements to minimize reflection losses, (3) by collecting an unusually large horizontal radiation fan (6 mrad) with the toroidal premirror, and (4) the optimization of the crystal optics to the soft x-ray range necessitating quasibackscattering crystal geometry (theta(Bragg,max)=82 degrees) delivering crystal limited resolution. The multipurpose beamline is in use for a variety of user facilities such as extended x-ray absorption fine structure, ((Bio-)EXAFS) near-edge x-ray absorption fine structure (NEXAFS), absorption and fluorescence spectroscopy. Due to the windowless UHV setup the k edges of the technologically and biologically important elements such as Si, P, and S are accessible. In addition to these experiments this beamline is now extensively used for photoelectron spectroscopy at high kinetic energies. Photon flux in the 10(11)-10(12) photons/s range and beamline resolving powers of more than E/DeltaE approximately 100.000 have been measured at selected energies employing Si (nnn) high order radiation in quasibackscattering geometry, thus photoelectron spectroscopy with a total instrumental resolution of about 150 meV is possible. This article describes the design features of the beamline and reports some experimental results in the above mentioned fields.     

Size effects in glass fragment identification by micro-x-ray fluorescence analysis

Energy-dispersive x-ray fluorescence (EDXRF) analysis with a lateral resolution of 300 μm has been used in scanning electron microscopy to carry out model experiments for the identification of small glass fragments. Small sample dimensions can produce size effects which cause intensity changes in the EDXRF spectra as compared with bulk specimen spectra. These effects can be analysed by means of the inelastically scattered Mo Kα source line as long as the x-ray spot size is smaller than the specimen dimension.     

激光等离子体X射线极化光谱研究

为了诊断激光等离子体X射线的极化光谱,研制了一种新型的基于空间分辨的极化谱仪。将平面晶体和球面弯晶色散元件在极化谱仪内正交布置,即在水平通道用PET平面晶体作为色散元件,而在垂直通道用Mica球面弯晶作为色散元件,球面半径为380mm。信号采用成像板进行接收,有效接收面积为30×80mm,从等离子体光源经晶体到成像板的光路约为980mm。物理实验首次在中国工程物理研究院激光聚变研究中心“2×10J激光装置”上进行,成像板获得了铝激光等离子体X射线的光谱空间分辨信号。实验结果表明该谱仪具有较高谱分辨率,适合激光等离子体x射线极化光谱的诊断。     

One-dimensional space resolving flat-field holographic grating soft x-ray framing camera spectrograph for laser plasma diagnostics

A 1D space resolving x-ray spectrum diagnostic system has been developed to study the radiation opacity of hot plasma on SG-II laser facility. The diagnostic system consists of a 2400 lines/mm flat-field holographic grating and a gated microchannel plate coupled with an optical CCD and covers the wavelength range of 5-50 A?. The holographic grating was compared with a ruled one by measuring the emission spectra from a laser-produced molybdenum plasma. The results indicate that the holographic grating possesses better sensitivity than the ruled grating having nearly similar spectral resolution. The spectrograph has been used in radiative opacity measurement of Fe plasma. Simultaneous measurements of the backlight source and the transmission spectrum in appointed time range in one shot have been accomplished successfully with the holographic grating spectrometer. The 2p-3d transition absorption of Fe plasma near 15.5 A? in has been observed clearly.     

Tunable laboratory extended x-ray absorption fine structure system

A new sensitive x-ray monochromator and detector system for performing extended x-ray absorption fine structure (EXAFS) measurements in the laboratory is described. The monochromator combines x-ray focusing optics with rapid elemental tunability. The detection system effectively removes glitches from the data stream, regardless of whether they are due to impurity lines from the x-ray source or if they are due to random instabilities in the incident beam. Used together with a high intensity rotating anode x-ray source, this system can provide synchrotronlike photon intensities, flexibility and resolution, with the easy access and control possible only in the laboratory.     

Note: study of extreme ultraviolet and soft x-ray emission of metal targets produced by laser-plasma-interaction

Different metal targets were investigated as possible source material for tailored laser-produced plasma-sources. In the wavelength range from 1 to 20 nm, x-ray spectra were collected with a calibrated spectrometer with a resolution of λ/Δλ = 150 at 1 nm up to λ/Δλ = 1100 at 15 nm. Intense line emission features of highly ionized species as well as continuum-like spectra from unresolved transitions are presented. With this knowledge, the optimal target material can be identified for the envisioned application of the source in x-ray spectrometry on the high energy side of the spectra at about 1 keV. This energy is aimed for because 1 keV-radiation is ideally suited for L-shell x-ray spectroscopy with nm-depth resolution.