A new kind of hard X-ray / gamma-ray optic is proposed. This optics may be useful for collecting primary X-rays or gammarays from a point source and direct secondary hard X-rays into a given direction. The main element of the proposed optic is a multichannel collimator, which is a glass poly-capillary tube. Incident gamma-rays or hard X-rays with energy E from a point source cross the channel walls of the collimator at a given angle to channel axis and produce secondary Comptonscattered hard X-rays with energy E1 < E. A small portion of the secondary, Compton-scattered hard X-rays, which are emitted in parallel to the center axis of each channel, transmit through the collimator without absorption, forming a hard Xray beam.
A prototype x-ray imaging system was built and tested for high-resolution x-ray radiography and tomography. The
instrument consists of a microspot x-ray tube with a multilayer optic, a parabolic compound refractive lens (CRL) made
of a plastic containing only hydrogen and carbon, and an x-ray detector. A rotation stage was added for tomography.
Images were acquired of both grid meshes and biological materials, and these are compared to images achieved with
spherical lenses. We found the best image quality using the multilayer condenser with a parabolic lens, compared to
images with a spherical lens and without the multilayer optics. The resolution was measured using a 155 element
parabolic CRL and a multilayer condenser with the microspot tube. The experiment demonstrates about 1.1 μm
We have fabricated and tested short focal-length compound refractive lenses for X-rays (CRLs) and considered its
application for focusing coherent beams. The lens is designed in the form of glass capillary filled by micro-air-bubbles
embedded into epoxy. The interface between the bubbles formed 90 to 196 spherical bi-concave microlenses with curvature
radius equals to the capillary one. When compared with CRLs manufactured using other methods, the micro-bubble lenses
have shorter focal lengths with higher transmission for moderate energy X-rays (e.g. 7 - 12 keV). The lenses are inexpensive
and are ideally suited for focusing X-rays generated by high power single pulsed operation coherent X-ray sources with
Source size 50-100 microns. We used beamline 2-3 at the Stanford Synchrotron Radiation Laboratory (SSRL) to measure
focal lengths between 100-150 mm and absorption apertures between 90 to 120 pm. Transmission profiles were measured
giving, for example, a peak transmission of 27 % for a 130-mm focal length CRL at 8 keV. The focal-spot sizes were also
measured yielding, for example, an elliptical spot of 5 × 14-μm2 resulting from an approximate 80-fold demagnification of
the 0.44 × 1.7 mm2 source.
There is a need for high brightness neutron sources that are portable, relatively inexpensive, and capable of neutron radiography in short imaging times. Fast and thermal neutron radiography is as an excellent method to penetrate high-density, high-Z objects, thick objects and image its interior contents, especially hydrogen-based materials. In this paper we model the expected imaging performance characteristics and limitations of fast and thermal radiography systems employing a Rose Model based transfer analysis. For fast neutron detection plastic fiber array scintllators or liquid scintillator filled capillary arrays are employed for fast neutron detection, and 6Li doped ZnS(Cu) phosphors are employed for thermal neutron detection. These simulations can provide guidance in the design, construction, and testing of neutron imaging systems. In particular we determined for a range of slab thickness, the range of thicknesses of embedded cracks (air-filled or filled with material such as water) which can be detected and imaged.
Two neutron microscope imaging experiments were performed at the Center for Neutron Research, at the National Institute for Standards and Technology (NIST) on the NG-7 30-Meter Small Angle Neutron Scattering Instrument. The NIST neutron source wavelength could be varied from 5 Å to 20 Å, and the neutron bandwidth could be varied. For both microscope experiments the image resolution was 5.0 mm, and was determined and limited by the NG-7 neutron detector’s 5.0 mm pixel size. The image acquisition times were set to 300 sec. In the first experiment the neutron source wavelength was set to 5 Å with an 11% bandwidth. A simple microscope with a 22.6x magnification, employing a compound refractive lens, composed of 201 aluminum (Al) biconcave lenses, was used to image a slit array in Cadmium (Cd) foil, located 139 cm downstream of the source. The Cd slit array consisted of 0.8 mm wide slits separated by 0.8 mm wide slats. The Al CRL had 1.98 mm radius of curvature, a 3.9 mm aperture, and a measured 1.2 cm field of view (FOV). An 85 lens version of this Al CRL had a measured 2.3 cm FOV and 9.4
x magnification, and was used to image at rat paw. The Cd slit array was placed upstream of the aluminum CRL at 74.5 cm object distance. In the second NIST experiment the neutron source wavelength was set to 8.5 Å with a 10% bandwidth. A simple microscope with a 22.5x magnification, employing a compound refractive lens, composed of 100 MgF2 biconcave lenses, was used to image materials and specimens containing hydrogen, whose main contrast mechanism for neutrons is incoherent scattering. The MgF2 CRL had a measured 2.4 cm FOV. The hydrogen-rich material imaged was a polypropylene (hydrogen-rich) grid, and the biological specimens were a scorpion, a rat paw, and a plant leaf, and they were situated 122 cm downstream of the source, and 78 cm upstream of the MgF2 CRL.
We have measured the intensity profile and transmission of x-rays focused by a series of bi-concave parabolic unit lenses fabricated in lithium and beryllium. For specified focal length and photon energy, lithium and beryllium compound refractive lenses (CRL) have a larger transmission, aperture size, and gain compared to aluminum, epoxy, and kapton CRLs. One Li CRL was composed of 335 bi-concave, parabolic unit lenses, each with an on-axis radius of curvature of 0.95 mm. This Li CRL achieved a 95 cm focal length at 8 keV with an
effective aperture of 1 mm, an on-axis (peak) transmission of 26 %, and an on-axis intensity gain of 18.9. The beryllium compound refractive lens was composed of 160 bi-concave unit lenses, each with a radius of curvature of 1.9 mm. The Be CRL achieved two-dimensional focusing at 6.5 keV with a gain of 1.5, peak transmission of 9 %,
focal length of 93 cm, and an effective aperture of 600 μm. Based upon the principle of spontaneous emission amplification in an FEL wiggler, coherent x-ray sources are being developed with wavelengths of 1-1.5 Å and source diameters of 50-80 μm, and the Be and Li CRL may be used to provide a small, intense image. For these
coherent x-ray source parameters, the large apertures of Be and Li CRLs enable intensity gains of 105 to 106.
We have fabricated and tested short focal-length compound refractive lenses (CRLs) composed of micro-bubbles embedded in epoxy. The bubbles were formed in epoxy inside glass capillaries. The interface between the bubbles formed 90 to 196 spherical bi-concave microlenses reducing the overall focal length inversely by the number of lenses.
When compared with CRLs manufactured using other methods, the micro-bubble lenses have shorter focal lengths, better imaging, and focusing qualities with higher transmissions and gains for moderate energy x-rays (e.g. 7 - 12 keV). We used beamline 2-3 at the Stanford Synchrotron Radiation Laboratory (SSRL) to measure focal lengths between 100-150 mm and absorption apertures between 90 to 120 μm. Transmission profiles were measured giving, for example, a peak transmission of 27 % for a 130-mm focal length CRL at 8 keV. The focal-spot sizes were also measured yielding, for example, an elliptical spot of 5 x 14-μm2 resulting from an approximate 80-fold demagnification of the 0.44 x 1.7 mm2 source. The measured gains in intensity over that of unfocused beam were between 9 and 26. Theoretical gain calculations that include spherical aberrations show that these values are reasonable. The micro-bubble technique opens a new opportunity for designing lenses in the 8-9 keV range with focal lengths less than 30-40 mm.
Compound refractive lenses (CRLs) are effective for collimating or focusing high-energy x-ray beams (50 - 100 keV) and can be used in conjunction with crystal optics in a variety of configurations, as demonstrated at the 1-ID undulator beamline of the Advanced Photon Source. As a primary example, this article describes the quadrupling of the output flux when a collimating CRL, composed of cylindrical holes in aluminum, is inserted in between two successive monochromators -- a modest energy resolution premonochromator followed by a high-resolution monochromator. The premonochromator is a cryogenically cooled, divergence-preserving, bent double-Laue Si(111) crystal device delivering an energy width ΔE/E ~10-3, sufficient for most experiments. The high-resolution monochromator is a four-reflection, flat Si(111) crystal system resembling two channel-cuts in a dispersive arrangement, reducing the bandwidth to ΔE/E < 10-4, as required for some applications. Tests with 67 keV and 81 keV photon energies show that the high-resolution monochromator, having a narrow angular acceptance of a few μrad, exhibits, a four-fold throughput enhancement due to the insertion of a CRL which reduces the premonochromatized beam's vertical divergence from 29 μrad to a few μrad. The ability to focus high-energy x-rays with CRLs having long focal lengths (tens of meters) is also shown by creating a line focus of 70 - 90 μm beam height in the beamline end-station with both the modest-energy-resolution and high-energy- resolution monochromatic x-rays.
Several laboratories are now in the process of designing and constructing coherent x-ray sources, and application of these beams for radiography and material studies is facilitated by having appropriate optical components to provide collimation or focusing. Control of x-rays can be achieved by employing elements that perform refraction, diffraction or reflection, as exemplified by a lens, grating or mirror, respectively. Of course, the maximum intensity of minimum image size that is obtainable from any of these elements is determined by diffraction effects. Using the parameters of the Liinac Coherent Light Source (LCLS) being studied at the Stanford Synchrotron Radiation Laboratory (SSRL), x-ray optical components can increase the beam intensity approximately eight orders of magnitude and provide submicron images. Performance comparisons are made between the zone plate, the phase zone plate, the compound refractive lens, the Fresnel compound refractive lens, and the parabolic mirror.
Refractive lenses have been used successfully to focus incoherent x-ray emission in the wavelength range from 2 to .5A with focal lengths on the order of one meter. A stack of N lens elements is employed to reduce the focal length by the factor N over a single element, and such a lens is terms a Compound Refractive Lens (CRL). Contrary to intuition, misalignment of parabolic lens elements doesn't alter the focusing properties and results in only a small reduction in transmission. Coherent x-ray sources are being developed with wavelengths of 1-1.5A and source diameters of 50- 80micrometers , and the CRL is ideally suited to produce a small, intense image. Chromatic aberration increase the size of the image and so it is important to provide chromatic correction to minimize the image dimensions. Pulse broadening due to the dispersion of the lens material is negligible. Intensity gain is in the range from 105 to 10+$6), where gain is defined as the intensity ratio in an image plane with and without the lens in place. Maximum image intensity is obtained when the CRL is placed a distance of 100 to 200 m from the source, and the typical diameter of the focused spot is about one micron.
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.
Transition and parametric radiators are proposed as sources for EUVL and XRL. Collimated soft x-rays and extreme UV (EUV) radiation can be generated using electron beams with moderate electron-beam energies, unlike synchrotron radiators, which require energies of greater than 300 MeV. Earlier work focused on using transition radiation in the 0.5-3.0 keV range with electron beam energies between 17-100 MeV for output wavelength around 1.4 nm. However, tunable quasi-monochromatic emission in the EUV as well as x-ray regions can be also obtained using parametric radiators. We propose that a compact betatron be used to recycle the beam through these radiators for higher x-ray efficiency. Experiments using storage rings and simulations using known betatron parameters are presented here that demonstrate the electron beam can be recycled through the thin radiators up to 300 times. With this increase in efficiency, the source output power is expected in the range of 100 mW.
In recent years, comprehensive design studies have been initiated on angstrom-wavelength free-electron laser (FEL) schemes based on driving highly compressed electron bunches from a multi-GeV linac through long undulators. The output parameters of these sources, when operated in the so-called self-amplified spontaneous emission mode, include lasing powers in the 10-100 GW range, full transverse and low-to- moderate longitudinal coherence, pulse durations in the 50- 500 fs range, broad spontaneous spectra with total power comparable to the coherent output, and flexible polarization parameters. In this paper we summarize the status of design studies of the x-ray optics system and components to be utilized in the SLAC linac coherent light source, a 1.5-15 angstrom FEL driven by the last kilometer of the SLAC three kilometer S-band linac. Various aspects of the overall optical system, selected instrumentation and individual components, radiation modeling, and issues related to the interaction of intense sub-picosecond x-ray pulses with matter, are discussed.
As a synchrotron equivalent, this paper presents a single- stepper, soft-x-ray source which offers high brightness, high collimation (less than 20 mr global and less than 2 mr local), modest operating vacuum, excellent spectrum and moderate cost. The x-rays are generated by a process called transition radiation (TR). Electrons of moderate energy (e.g. 17 - 100 MeV) pass through thin-metal foils producing a forward- directed cone of x-rays whose photon energies can be between 0.5 and 3 keV. The optimum radiator consists of many thin- metal foils, e.g. beryllium, which are separated by vacuum. The x-ray wavelength an be optimized for highest photoresist sensitivity, e.g. 1.4 nm. A computer simulation shows that for beam-shaping (slit formation) and collimation, a single grazing-angle optic transforms the radiator cone into a slit (5 mm by 26 mm) in the 1X wafer image plane, having an energy density of 15 - 60 mJ/cm2. This slit is then scanned for dose uniformity. In a proof-of-principle experiment, an apparatus utilizing a Au-coated grazing-angle optic was used to focus transition radiation to a slit (7 mm by 16 mm) in the image plane at 631 mm from the optic and 881 mm from the TR radiator. Intensity variation across the longitudinal direction (approximately 10 mm) of the slit was less than 5%.