A high power picosecond soft x-ray source is generated by a compact, modular, diode pumped solid state laser BriteLightTM. Three x-ray source version are constructed from laser modules with increasing power. The power of the x-ray sources is tailored to potential applications. The building block of such a modular system is a 3 Watt x-ray power source with 1.1 keV x-ray photon energy. The laser system is very compact with dimensions of 4 ft X 3 ft X 1 fit. It is composed of a laser master oscillator, pre-amplifier and one power amplifier. A four laser amplifier system was also constructed in order to generate 12 W of x-rays for application to x-ray lithography.
A description is given in this paper on the present progress of a compact laser synchrotron femtosecond x-ray source based on the inverse Compton scattering of high energy femtosecond laser pulses by high energy electrons. The present research program is reviewed by the target energy and number of the femtosecond x-ray photons for phase 1 (1996 - 2000) and phase II (2001 - 2004). Possible examples are considered for ultrafast imaging and pump- probe experiments by using this x-ray source.
We present the most recent data concerning the performances of the table-top laser driven electron and x-ray source developed in our laboratory. X-ray pulses are produced by a three-step process which consists of the photoelectron emission from a thin metallic photocathode illuminated by 16 ps duration laser pulse at 213 nm. The e-gun is a standard pierce diode electrode type, in which electrons are accelerated by a cw electric fields of 12 MV/m. The photoinjector produced a train of 90 - 100 keV electron pulses of approximately 1 nC and 40 A peak current at a repetition rate of 10 Hz. The electrons, transported outside the diode, are focused onto a target of thulium by magnetic fields produced by two electromagnetic coils to produce x-rays. Applications to low dose imagery of inert and living materials are also presented.
Powerful pulsed soft x-ray point sources are being developed, driven by the Zebra z-pinch at the Nevada Terawatt Facility. A wide variety of x-ray and EUV pulses can be generated, depending on the z-pinch load. X-ray and EUV pulses have been produced with duration from 1.5 ns to 40 ns, energy from 30 J to 9 kJ, and effective source size smaller than 100 micrometers . These pulses will be used for the development of plasma diagnostics, for the study of surface physics, and for microscopy.
In this paper the speed of microscopic droplets used as targets for laser-plasma soft x-ray generation is investigated. The speed is measured for a variety of liquids with different hydrodynamic properties and at different pressures. A theoretical model is then adapted to predict the speed of the jet, given the applied pressure and the physical properties of the liquid. Since certain liquids with low surface tension and cryogenic liquids are interesting for laser-plasma generation, obtaining a model for the speed of the liquid is important, as the speed cannot be easily measured for these liquids.
A compact device, based on fast capillary discharge plasmas, is used as an intense EUV and soft x-ray source of radiation. The plasma is created by a discharge of low-inductance capacitors (30 nF) through a capillary (2 mm diameter, 20 mm length). Two types of capillary are used: a polyacetal (empty) and a gas-filled (Ar, Xe). All components are assembled in a coaxial geometry. The total size of the device including capacitors, switch and capillary is 30 cm long and 25 cm in diameter. Discharge current is monitored using a shunt circuit.
In order to evaluate the performance of multilayer optics, we have successfully developed a simple, laboratory-sized reflectometer that can be operated readily on a routine basis. This reflectometer makes use of a single line emission at the wavelength of 12.98 nm from a CO2 gas-jet laser-plasma x-ray source that can be readily operated on a routine basis. Our reflectometer achieved repeatability of less than +/- 0.8% in reflectivity measurements. The peak reflectivity of a sample determined by calculation based on multilayer mirror parameters obtained from our reflectometer was within +/- 1.3% of that obtained by an SR-based reflectometer. These results confirm that our reflectometer performs well enough to evaluate multilayer optics.
This paper describes a new method for improved determination of multilayer period using a soft x-ray reflectometer based on a line-emitting high-brightness water-window liquid-jet laser- plasma source. The use of line emission with well-known wavelengths allows accurate measurements of multilayer period without source monochromatization and calibration. By using a new multi-line data analysis procedure the multilayer period of W/B4C mirrors can be determined with an accuracy of 0.001 nm.
For X-ray structure determination of biological macromolecular crystals interest has shifted to the use of very small crystals (less than 0.01 mm in diameter) with relatively large mosaic spreads (up to 10-2 radians). For this purpose we are investigating mono-capillary optics and planar-parabolic and planar-elliptical mirrors. For studies of this type a low-power microfocus source with appropriate optics can compete favorably with high-power rotating-anode x-ray generators.
Close coupling of microfocus x-ray sources and polycapillary collimating optics allows for large collecting angle of the optics for small, parallel beam x-ray diffraction applications. Two polycapillary collimating optics were designed and fabricated for use with a microfocus x-ray tube that has a small spot and short spot-to-BE-window distance (2.2 mm). Both optics generated a quasi-parallel x-ray beam of 1.5 mm in diameter. The x-ray intensity obtained from the Cu-anode source was 1.9 X 109 cps (Cu K(alpha) ) at 40 kV and 60 W, and the beam divergence was measured to be 2.3 mrad. The intensity obtained from the Mo-anode source was 1.3 X 108 cps (Mo K(alpha) ) at 50 kV and 40 W, and the beam divergence was 1.6 mrad. These are equivalent to what one could achieved with a 5.4 kW Cu source and a 1.3 kW Mo source, respectively, when using conventional pinhole collimators. The approaches to achieve small beam divergence using polycapillary optics are discussed.
This paper describes the design and performance of a low power protein crystallography system using polycapillary optics. The characterization of the source and polycapillary optics are presented. Three optic types: collimating, slightly focusing and strongly focusing optics have been used in low power source-optic combination systems. The source-collimating optic and source- slightly focusing optic systems were used to collect data sets for chicken egg-white Lysozyme with conventional sample oscillation during data collection. The data sets show high quality by analysis with a conventional software package, DENZO. Still diffraction patterns without oscillation have also been obtained by a low power source-strongly focusing optic combination. These patterns have been analyzed by developing software for processing diffraction patterns obtained with strongly convergent X-ray beams. The directions of future work and system improvements are also discussed.
Doubly curved crystals of Mica, Ge and Si were bent according to Johann-Geometry. Point-to-point focusing of characteristic x-rays can be used to create a highly intense focal spot (50 micrometers FWHM) of 6.7 X 108 photons/s using a doubly curved Ge crystal and a 15 W Cr x-ray source. The output focal spot size was shown to be dependent on the spot size of the source. Focal spots of less than 50 micrometers were achieved. Doubly curved crystals have useful properties for monochromatic micro x-ray fluorescence measurements.
Performance of Ni/C, Ni/B4C, Mo/B4C and W/B4C multilayers in the energy range E > 8 keV is considered by simulation of x-ray reflectivity and resolution of 1st order Bragg reflection at three different photon energies. The results indicate, that Ni/C and Ni/B4C multilayers show highest theoretical reflectivities of R > 80% for Cu K(alpha) - radiation and also above the Mo K-edge (E equals 20.04 keV) at 30 keV. For Mo K(alpha) -radiation a reflectivity of R > 90% can be achieved by the use of Mo/B4C multilayers. For applications, where period thicknesses d < 3 nm and high reflectivities are required W/B4C multilayers can be used. Theoretical values are compared with X-ray reflectometry results, which were executed at 75 period Ni/C, Ni/B4C and Mo/B4C multilayers, fabricated by pulsed laser deposition (PLD) technology on Si substrates. Amorphous or nanocrystalline structures of single layers, smoothest interfaces and high reproducibility of single layer thickness across the entire layer stack are the results of this high precision PLD process.
Design, technology, and applications of x-ray graded multilayer mirrors are discussed in the paper. Various mathematical optimization routines, such as steepest-descent, Powell, conjugated gradients, or needle-variation methods can be used to design depth-graded multilayers. The technology of manufacturing of this type of multilayers is based on the variation of a deposition time, while the spatial distribution of the deposition rate is uniform. Magnetron sputtering technique provides the accuracy of better than 1 angstrom for W/C structures. Laterally graded multilayers with desired spatial period distribution can be manufactured by magnetron sputtering technique using specially shaped slits positioned between the anode and the sample. Laboratory applications of graded mirrors include compact double- mirror conjugated focusing system of a Kirkpatrick-Baez type, programmable x-ray deflector, parabolic collimator with the output beam's angular divergence of 12 arc seconds, and dark- field refraction contrast imaging using multilayer mirrors with resonant absorption.
Theoretical considerations of the parameters that enable the construction of compound refractive lenses are treated in this writing. The best performing compound refractive lenses that have been constructed to date were made by Adelphi Technology Inc. stacking individual paraboloidal lenses made of polyimide (KaptonTM). Polyimide lenses are capable of focusing photon with energies between 4 keV and 60 keV with focal lengths below 60 cm. They are not affected much by small misalignment of the individual lenses. Surface finish is less stringent than for visible light lenses. The increase in intensity in the image plane relative to the intensity that would have been obtained without a lens or gain measured at the experimental station of a bend magnet beam line was found to be 5.5 at 9 keV x-rays with transmission of 10% at that same energy. The measured values were in good agreement with the theoretical predictions at all wavelengths tested.
Grazing incidence micromirrors of ellipsoidal or parabolic shape with apertures below 1 mm have numerous potential applications in many areas of applied physics, molecular biology and material research. One of the most important applications of such optics is in its combination with microfocus x-ray generator. Extremely intense collimated or focused high-quality x-ray beams from tabletop equipment can be obtained in this way. It is shown that though developed primarily for macromolecular crystallography, this combination gave excellent results also in other fields of science and technology. Computer ray-tracing and experimental data characterizing mirror and x-ray beam parameters in typical applications are presented.
Two new applications of monolithic polycapillary x-ray optics were explored. One was to improve the detection sensitivity of microbeam x-ray fluorescence analysis for radioactive samples. One focusing optic was used to focus x-rays onto a small area of the sample, and the second focusing optic was used as a spatial filter to collected x-ray fluorescence from the area defined by the first optic. The radiation background from the radioisotope in the sample was significantly reduced, and therefore the detection sensitivity for such samples was greatly enhanced. The other application was using a focusing optic to improve performance of position-sensitive-detector-based wavelength- dispersive x-ray fluorescence analysis. The small, intense excitation beam obtained with a focusing optic greatly increased the count rate of the measurement, thus improving the detection sensitivity of the system. Some new progresses achieved in monolithic polycapillary optics design and manufacturing are also discussed.
An experimental-analytical technique for x-ray phase retrieval and consequent crystal structure-factor determination is tested and discussed in the cases of high- (rotating anode or synchrotron radiation) or low-flux (fixed anode x-ray tubes) radiation sources. Experimentally measurable reflectivity magnitudes, using a rotating anode or conventional x-ray tube source, affect the directly reconstructed profile of the complex crystal structure-factor. Thermal and point defect diffuse scattering contaminates the tails of the Bragg diffracted intensity. A numerical procedure developed for the regularization of the directly reconstructed complex structure-factor allows the elimination of parasitic fringes in the resulting crystal-lattice strain profiles. In addition, replacement of plus/minus infinity limits in a mathematical formalism of the reconstruction procedure by actually measured experimental values of the scattering vector in practice affects the resulting profile of the complex crystal structure factor.
Polycapillary x-ray optics can be used as pre- or post-patient optics to design mammographic imaging systems with higher resolution, greater contrast, and a lower absorbed patient dose. A multi-fiber collimating prototype optic, used as pre-patient beam shaper, provides 39% transmission efficiency at 17.5 keV, good uniformity, and only 3.9 mrad divergence. Experimental optics characterization results are compared with detailed computer simulations including analysis of optical defects such as channel waviness and bending. The collimating optic was used to produce monochromatic radiation by diffracting from a silicon crystal. The monochromatic contrast, measured at 8 keV with a polypropylene phantom, was 5 times greater than the measured polychromatic contrast.
Many medical imaging and industrial applications for x rays require large area optics with good scatter rejection. Preliminary scatter rejection and contrast measurements show that a prototype long borosilicate optic increases the contrast by a factor of 1.7 by decreasing the scatter transmission nearly a factor of 10 at 20 keV. Since borosilicate optics have higher scatter transmissions at high energies, the optics have to be fairly long to give good scatter rejection at high energies. However, long optics are complex to manufacture and have increased defect rates. Lead glass would allow the optic to be much shorter and still give good contrast enhancement, because of the superior absorption of leaded glass. In order to investigate the feasibility of using leaded glass polycapillary optics for these applications, measurements and simulations have been performed on the behavior of leaded glass polycapillary fibers in the 9 - 80 keV energy range.
An ultra low timing-jitter pulsed X-ray source was developed. The low jitter characteristic of this X-ray was obtained by using two q-switched Nd:YAG lasers: one was used for triggering a Marx generator, which supplies pulsed high voltage to a flash X-ray source, and the other was for triggering X-ray emission. The pulse width of the X-ray was about 50 ns and the timing-jitter was several nanoseconds. The low timing jitter enabled us to take an X-ray photograph with multiple exposure, so that a clear image of a high-speed rotating fan was obtained.
An x-ray optic suitable for use in x-ray proximity lithography is described. It employs multiple flat mirror facets arranged at grazing incidence, each of which creates an optically independent channel that covers the entire target. The facets are arranged so that many channels can simultaneously illuminate the target, thereby achieving high flux at the target with high uniformity. We report laboratory testing that shows uniformity better than +/- 0.4% across 40 mm at 1 keV.
Polycapillary fibers and a prototype collector for high energy x rays with a 2 m focal length have been fabricated and characterized. Measurements of a prototype collector, performed in collimating mode, show that the optic has high transmission, good uniformity, and small exit divergence. The transmission as a function of energy was analyzed using an extended single fiber geometrical optic simulation and the result shows that the simulation fits the data fairly well. Scatter transmission and contrast enhancement were measured in focusing mode using a parallel beam input.
This research is a continuation of our activity on the development and study of glass-capillary optics devices that started in 1974. We presented new results of the experimental study of a strongly nonuniform spatial distribution of output keV and sub-keV radiation, that transported by different types of glass mono- and polycapillary converters from point x-ray laser plasma and z-pinch plasma sources.
The use of bent crystals with high integrated reflectivity in focusing crystal spectrometers (Johann and von Hamos schemes) is considered. It is shown that in a von Hamos scheme mosaic focusing takes place. Thus a mosaic crystal simultaneously provides high spectral resolution and high efficiency. Expressions for the mosaic focusing are obtained. Focusing mica and graphite crystal von Hamos spectrometers (radius of crystal curvature is 20 mm) are investigated: spectral and spatial resolution and absolute efficiency are measured in a spectral range of 2 - 2.6 angstroms using laser-produced plasma and iron isotope x-ray sources. The mica crystal spectrometer showed high spatial (up to 10 micrometers ) and spectral ((lambda) /(delta) (lambda) approximately 1000) resolution, whereas the graphite spectrometer showed very high efficiency (30 - 70 times higher than the mica crystal) and moderate spectral resolution ((lambda) /(delta) (lambda) approximately 500 - 750). In the latter case mosaic focusing is observed: spectral resolution is 10 - 15 times higher than spectral resolution determined by the mosaic spread of the crystal ((lambda) /(delta) (lambda) approximately 50). The results allow one to estimate a maximum efficiency for focusing crystal spectrometers. Prospects for using the von Hamos spectrometers for x-ray spectroscopy and x-ray fluorescence are considered.
An experimental model of an industrial micropinch x-ray source is described on the basis of a low inductance vacuum spark. It was designed and tested for applications in x-ray lithography, x-ray microscopy, surface processing (micro-relief leveling) and structural modification of thin dielectric layers. The error analysis of proximity method and test results confirmed the adequacy of its application to produce microchips for the microelectronic industry with spatial resolution of < 0.1 (mu) . The x-ray microscopy of human and rabbit blood and tissue cells was performed using the proximity shadow printing method with the sensitive polymer detectors or resists.