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X-Ray Optics & Sources

2007

Title: High resolutions x-ray microscope
Date: May 2007
Publication type: Peer reviewed journal article
Publication: Appl. Phys. Lett. 90
Authors: C. K. Gary, H. Park, L. W. Lombardo, M. A. Piestrup, J. T. Cremer, R. H. Pantell, Y. I. Dudchik
Abstract: The authors present x-ray images of grid meshes and biological material obtained using a microspot x-ray tube with a multilayer optic and a 92-element parabolic compound refractive lensCRL made of a plastic containing only hydrogen and carbon. Images obtained using this apparatus are compared with those using an area source with a spherical lens and a spherical lens with multilayer condenser. The authors 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 microns resolution.


Title:
Using of a microcapillary refractive X-ray lens for focusing and imaging
Date: 2007
Publication type:
Publication:
Spectrochimica Acta Part B 62 598-602
Authors: Yu.I. Dudchik, F.F. Komarov, M.A. Piestrup, C.K. Gary, H. Park, J.T. Cremer
Abstract: The microcapillary lens, formed by air bubbles in a hollow core glass capillary filled with epoxy, is a novel design of a compound refractive lens for X-rays. The epoxy enclosed between two air bubbles has the form of a biconcave lens and acts as a positive lens for X-rays. Each individual lens is spherical with radius of curvature equal to the inner radius of the capillary. Up to 500 individual biconcave lenses can be formed in a single capillary with diameters from 50 to 500 μm. Due to the small radius of curvatures that can be achieved, microcapillary lenses typically have shorter focal lengths than those made by compression or injection molding. For example, microcapillary lenses with a focal length about 5 cm for 8 keV X-rays and 50-micron aperture are readily available.

We have produced a set of lenses in a 200-micron inner-diameter glass capillary with 100–350 individual microlenses and measured their parameters at the Stanford Synchrotron Radiation Laboratory and at the Advanced Photon Source. Our investigations have also shown that the lenses are suitable for imaging applications with an X-ray tube as a source of X-rays. A simple X-ray microscope is discussed. The microscope consists of a copper anode X-ray tube, X-ray lens and CCD-camera. The object, lens and CCDcamera were placed in-line at distances to satisfy the lens formula. It is shown that the field of view of the microscope is about 1 mm and resolution is equal to 3–5 microns.

2004

Title: Microspot x-ray focusing using short focal-length compound refractive lenses
Date: November 2004
Publication type: Peer reviewed journal article
Publication: Review of Scientific Instruments 75 (11) 4651-55 (2004)
Authors: Y.I. Dudchik, N.N. Kolchevsky, F.F. Komarov (Institute of Applied Physics Problems, Kurchatova), M.A. Piestrup, J.T. Cremer, C.K. Gary, H. Park (Adelphi Technology Inc), A.M. Khounsary (Argonne National Laboratory, Illinois)
Abstract: We have fabricated and tested short focal-length compound refractive lenses (CRLs) composed of microbubbles embedded in epoxy encased in glass capillaries. The interface between the bubbles formed 90 to 350 spherical biconcave microlenses reducing the overall focal length inversely by the number of lenses or bubbles. When compared with CRLs manufactured using other methods, the microbubble lenses have shorter focal lengths with higher transmissions and larger gains for moderate energy x rays (e.g., 7–20 keV). We used beamline 2–3 at the Stanford Synchrotron Radiation Laboratory and beamline 5BM-D-DND at the Advanced Photon Source to measure focal lengths between 100–250 mm with lens apertures varying between 97 and 321 mm. Transmission profiles were measured giving, for example, a peak transmission of 46% for a 240 mm focal length CRL at 20 keV. The focal-spot sizes were also measured yielding, for example, a vertical spot size of 1.2 mm resulting from an approximate 20-fold demagnification of the APS 23 mm source size. The measured gains in intensity over that of unfocused beam were between 9 and 26. © 2004 American Institute of Physics. [DOI: 10.1063/1.1809289]


Title:
X-ray imaging of an X-pinch plasma with a bubble compound refractive lens
Date: October 2004
Publication type: Peer reviewed journal article
Publication: Review of Scientific Instruments 75 (10) 3950-2 (2004).
Authors: C.K. Gary (Adelphi Technology, Inc), S.A. Pikuz, M.D. Mitchell, K.M. Chandler, T.A. Shelkovenko, D.A. Hammer (Laboratory of Plasma Studies, Cornell University), Yu.I. Dudchik (Institute of Applied Physics Problems, Kurchatova, Minsk, Belarus)
Abstract: We present diagnostic images taken of an X-pinch plasma x-ray source driven by the XP pulser s100 ns, 500 kAd at Cornell University using an x-ray bubble compound refractive lens. The lens consists of a 200 mm inside diameter glass capillary that contains about 100 biconcave microlenses formed by a string of bubbles in epoxy. A precise system for lens alignment with of 3–5 arcmin accuracy is described. X-ray images of four-wire X pinches were obtained with a spatial resolution of approximately 2 mm.

2003

Title: X-ray Optics for 50-100 keV undulator radiation using crystals and refractive lenses
Date: 2003
Publication type: Conference Proceedings
Publication: Proc. SPIE 5195 pp63-75, (2003)
Authors: S. D. Shastri, A. Mashayekhi (Advanced Photon Source, Argonne National Laboratory, Argonne), J. T. Cremer and M. A. Piestrup (Adelphi Technology, Inc)
Abstract: 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 Delta_E/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 Delta_E/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 fourfold 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. Crystals, Multilayers, and Other Synchrotron Optics, edited by Tetsuya Ishikawa, Albert T. Macrander, James L. Wood, Proceedings of SPIE Vol. 5195 (SPIE, Bellingham, WA, 2003) · 0277-786X/03/$15 · doi: 10.1117/12.506374


Title: Large aperture compound refractive lenses

Date: 2003
Publication type: Conference Proceedings
Publication: SPIE, 5194, 62-89 (2003).
Authors: J. T. Cremer, M. A. Piestrup, C. K. Gary, R. H. Pantell
Abstract: 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 Angstroms and source diameters of 50-80 microns, 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 10^5 to 10^6.


Title: Short focal-length compound refractive lenses for x-rays
Date: 2003
Publication type: Conference Proceedings
Publication: SPIE 5194, 56 (2003).
Authors: Yury I. Dudchik, Nicolai N. Kolchevsky, Fadei F. Komarov, Melvin A. Piestrup, J. Theodore Cremer, Charles K. Gary, Richard H. Pantell
Abstract:
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 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 microns. Transmission profiles were measured giving, for example, a peak transmission of 27 % for a 126- mm focal length CRL at 8 keV. The focal-spot sizes were also measured yielding, for example, an elliptical spot of 5 x 14-microns^2 resulting from an approximate 80-fold demagnification of the 0.44 x 1.7 microns^2 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.


Title:
Large aperture compound lenses made of lithium
Date: 2003
Publication type: Peer reviewed journal article
Publication: Rev. Scient. Instrum. 74, 2262, (2003).
Authors: J. T. Cremer , M. A. Piestrup, H. R. Beguiristain, C. K. Gary, and R. H. Pantell
Abstract: We have measured the intensity profile and transmission of x rays focused by a series of biconcave parabolic unit lenses fabricated in lithium. For specified focal length and photon energy lithium compound refractive lenses (CRL) have a larger transmission, aperture size, and gain compared to aluminum, kapton, and beryllium CRLs. The lithium compound refractive lens was composed of 335 biconcave, parabolic unit lenses each with an on-axis radius of curvature of 0.95 mm. Two-dimensional focusing was obtained at 8.0 keV with a focal length of 95 cm. The effective aperture of the CRL was measured to be 1030 microns with on-axis (peak) transmissions of 27% and an on-axis intensity gain of 18.9.


Title: Characteristics of the Thick, Compound Refractive Lens
Date:
2003
Publication type: Peer reviewed article
Publication: Applied Optics, 42, 719 (2003).
Authors: R. H. Pantell, J. Feinstein, H. R. Beguiristain, M. A. Piestrup, C. K. Gary, and J. T. Cremer
Abstract: A compound refractive lens (CRL), consisting of a series of N closely spaced lens elements each of which contributes a small fraction of the total focusing, can be used to focus x rays or neutrons. The thickness of a CRL can be comparable to its focal length, whereupon a thick-lens analysis must be performed. In contrast with the conventional optical lens, where the ray inside the lens follows a straight line, the ray inside the CRL is continually changing direction because of the multiple refracting surfaces. Thus the matrix representation for the thick CRL is quite different from that for the thick optical lens. Principal planes can be defined such that the thick-lens matrix can be converted to that of a thin lens. For a thick lens the focal length is greater than for a thin lens with the same lens curvature, but this lengthening effect is less for the CRL than for the conventional optical lens.


Title:
Grazing Incidence Parametric X-Ray From Multilayer Mirror
Date: 2003
Publication type: Peer reviewed journal
Publication: Phys. Rev. E. 68, 1063, (2003)
Authors: N. N. Nasonov, V. V. Kaplin, S. R. Uglov, M. A. Piestrup and C. K. Gary


Title:
X-rays from relativistic electrons in a multilayer structure
Date: 2003
Publication type: Peer reviewed journal
Publication: Phys. Rev. E. 68, pp. xxx (2003).
Authors: N. N. Nasonov, V. V. Kaplin, S. R. Uglov, M. A. Piestrup and C. K. Gary
Abstract: A dynamic diffraction theory of x-ray emission by relativistic electrons crossing a finite-thickness multilayer mirror (e.g., alternating layers of W and B4C) is developed, taking into account both diffracted transition and parametric radiation mechanisms. Simple formulas describing the characteristics of the total emission from either thin nonabsorbing or thick absorbing multilayers are derived. These formulas show that a multilayer radiator can be brighter and more efficient than crystalline ones. Good agreement between theory and prior experimental results is also shown. Thus the theory and its experimental verification demonstrate the possibility of a tunable quasimonochromatic x-ray source whose efficiency can be larger than that of other novel x-ray sources.

2002

Title: X-ray focusing using compound lenses made of Beryllium
Date:
2002
Publication type: Peer reviewed journal
Publication: Optics Letters, 27, 778-780 (2002).
Authors: H. R. Beguiristain, J. T. Cremer, M. A. Piestrup, C. K. Gary and R. H. Pantell

Title: Tunable, monochromatic x-rays using the internal beam of a betatron
Date:
6 May 2002
Publication type: Peer reviewed journal
Publication: Applied Physics Letters, Vol. 80 No. 18, 3427-3429 (2002).
Authors: V. V. Kaplin, S. R. Uglov (Nuclear Physics Institute, Tomsk Polytechnic University, P. O. Box 25, Tomsk 634050, Russia), O. F. Bulaev, V. J. Goncharov, A. A. Voronin (Laboratory of Radiation Physics, Belgorod State University, Studencheskaja 12, 308007 Belgorod, Russia) , M. A. Piestrup, C. K. Gary (Adelphi Technology Inc), M. K. Fuller (OSMIC Incorporated, 201 Hoffman Avenue, Suite 6, Monterey, California 93940)
Abstract: Tunable, monochromatic x rays from thin radiators mounted inside a betatron have been observed. Parametric x-ray radiation (PXR) was generated by 33-MeV electrons passing multiple times through three radiators: a 43-micron-thick Si crystal, a 400-mm-thick graphite crystal, or a 310-layered-pair (W and B4C, d=14.86 Angstroms multilayer. The pulse-height spectrum of the radiation ~5 to 30 keV) was obtained and was tuned by rocking the crystal or multilayer relative to the electron-beam direction. The experimental results appear to follow theoretical predictions for PXR emission with some modification required for the curved trajectory of the electrons.


Title:
Thin betatron radiators for more efficient x-ray generation
Date: 2002
Publication type:
Publication:
REVIEW OF SCIENTIFIC INSTRUMENTS VOLUME 73, NUMBER 1 JANUARY 2002
Authors: V. V. Kaplin, S. R. Uglov, O. F. Bulaev, V. J. Goncharov, M. A. Piestrup and C. K. Gary
Abstract: We present experimental evidence that electrons of modest energy are making multiple passes through thin targets placed inside a betatron toroid, thus increasing their bremsstrahlung emission efficiency. Thin Cu, Be, W, and Mylar targets of thicknesses between 1025 to 3.531023 radiation lengths were used. The number of passes through the thin radiators were obtained using either the bremsstrahlung photon densities or angular distributions. The number of passes of 33-MeV electrons through the thin radiators was estimated to be 590 for a 1-mm-thick Cu foil, 171 for 5-microns Cu, 30 for 15-microns Cu, 200 for 20-microns Be, 51 for 60-microns Be, 20 for 200-microns Be, 460 for 3-microns-thick Mylar, and 123 for 2-microns W foils. The multiple-pass effect can be useful for increasing the efficiency of novel x-ray sources such as transition and parametric radiators.

2001

Title: Refractive lenses for coherent x-ray sources
Date: 2001
Publication type: Peer reviewed journal
Publication: Applied Optics 40, 5100 (2001).
Authors: R. H. Pantell, J. Feinstein, H. R. Beguiristain, M. A. Piestrup, C. K. Gary and J. T. Cremer
Abstract: Incoherent x rays in the wavelength interval from approximately 0.5–2 Å have been focused with refractive lenses. A single lens would have a long focal length because the refractive index of any material is close to unity; but with a stack of N lens elements the focal length is reduced by the factor N, and such a lens is termed a compound refractive lens (CRL). Misalignment of the parabolic lens elements does not alter the focusing properties and results in only a small reduction in transmission. Based on the principle of spontaneous emission amplification in a FEL wiggler, coherent x-ray sources are being developed with wavelengths of 1–1.5 Å and source diameters of 50–80m; and the CRL can be used to provide a small, intense image. Chromatic aberration increases the image size by an amount comparable with the diffraction-limited size, and so chromatic correction is important. Pulse broadening through the lens that is due to material dispersion is negligible. The performance of a CRL used in conjunction with a coherent source is analyzed by means of the Kirchhoff integral. For typical parameters, intensity gain is 10^5 –10^6 , where gain is defined as the intensity ratio in an image plane with and without the lens in place. (There may be some confusion concerning the usage of the wordintensity. As employed in this manuscript, intensity, also called irradiance, refers to power per unit area. This is a commonly accepted usage for intensity, although there are places in the literature where the term radiant incidence is reserved for this definition and intensity refers to power per unit solid angle.) The image intensity is maximized when the CRL is placed 100–200 m from the source, and the diameter of the diffraction-limited spot is approximately 0.12 microns

2001

Title: Compound x-ray refractive lenses made of polyimide
Date: 2001
Publication type: Conference proceedings
Publication: Proc. SPIE Vol. 4144, p. 155-164 (2001).
Authors: H. R. Beguiristain, J. T. Cremer, M. A. Piestrup, C. K. Gary, R. H. Pantell and J. Feinstein
Abstract: Theoretical considerations of the parameters that enable the construction of compound refractive lenses are treated in this writing. The best performing compound refractive lenses (CRLs) that have been constructed to date were made by Adelphi Technology Inc. stacking individual paraboloidal lenses made of polyimide (KaptonB). 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. Because of smaller source sizes and more collimated beams the gain of Kapton@ CRLs scales about three orders of magnitude higher on undulator beam lines at third generation x-ray sources compared to the results obtained at the bending magnet x-ray source, with dimensions 445 pm by 1700 pm placed at 16m from the lens, used in this work. Even more dramatic gains of lo6 will be obtained at coherenyt x-ray sources such as the LCLS. Gain and transmission of polyimide CRLs have been improved and their performance enhanced to surpass any CRLs previously developed and permitting focusing and imaging at lower energies. There is still much room for improvement of these lenses in all aspects of their development particularly increasing their aperture and transmission and improving their surface quality. Because of the source characteristics, synchrotron facilities in particular those with considerable production of coherent x-ray photons, will greatly benefit from the development of refractive lenses such as those being demonstrated in this writing.


Title: Focusing coherent x-rays with refractive optics
Date:
2001
Publication type: Conference proceedings
Publication: Proc. SPIE Vol. 4143, p. 109-117 (2001).
Authors: R. H. Pantell, J. Feinstein, H. R. Beguiristain, M. A. Piestrup, C. K. Gary and J. T. Cremer
Abstract: Refractive lenses have been used successfully to focus incoherent x-ray emission in the wavelength range from 2 to .5 A 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 termed 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 l-1.5 A and source diameters of 50-80 pm, and the CRL is ideally suited to produce a small, intense image. Chromatic aberration increases 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 10^5 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.


Title:
Compound Refractive Lenses for Novel X-ray Sources
Date: 2001
Publication type: Peer reviewed journal
Publication: Nuclear Instruments and Methods B 173, 170-177 (2001).
Authors: M. A. Piestrup, H. R. Beguiristain, C. K. Gary, J. T. Cremer, R. H. Pantell and R. Tatchyn
Abstract: We have measured the intensity profile of X-rays focused by a linear array of closely spaced spherical lenses fabricated using Mylar (C5H4O2). We have experimentally demonstrated that we can achieve two-dimensional focusing for photon energies between 7 and 9 keV with imaging distances of less than 1 m. For example, using 8-keV X-rays we have achieved full-width-at-half-maximum (FWHM) linewidths down to 27.5 microns at a distance of only 62 cm from the lens. The effective aperture of the lens was measured to be about 390 microns with 38% transmission at 9 keV. A synchrotron source having source-size dimensions of 0.44x1.7 mm^2 was utilized for the experimental work. Such lenses are seen as useful for focusing and increasing the intensity of novel X-ray sources that are directional and have small source size (sigma < 1 mm).


Title: The effect of unit lens alignment and surface quality on compound refractive lens performance

Date: 2001
Publication type: Peer reviewed journal
Publication: Rev. Scient. Instrum. 72, 48-52 (2001).
Authors: R. H. Pantell, J. Feinstein, M. A. Piestrup, H. R. Beguiristain, C. K. Gary and J. T. Cremer
Abstract: The required alignment tolerances and surface roughness for unit lens elements in a compound refractive lens (CRL) for x rays are discussed. Contrary to what one might expect and what has been stated in the patent literature, alignment tolerances are large and for typical parameter values the effect of misalignment is minor. For a parabolic lens the focusing properties of the CRL are unaltered by misalignment and there is a small increase in absorption. For a lens with spherical aberration, there is a slight change in focal length, a minor translation of the image, and a small increase in absorption. This article also shows that lens gain is not appreciably reduced if the phase shift that is introduced by the roughness is limited to (+/-)pi/4 or if the transverse period of the roughness exceeds a specified value. The CRL can benefit from a managed misalignment of the elements to reduce the phase error introduced by surface imperfections of the lens.


Title: Optics for Coherent X-ray Sources

Date: 2001
Publication type: Conference proceedings
Publication: Proc. SPIE 4500, 123-132 (2001).
Authors: R.H. Pantell, J. Feinstein, M.A. Piestrup, H.R. Beguiristain, and C.K. Gary
Abstract: Several laboratories are now in the process of designing and constructing coherent x-ray 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 exempified by a lens, grating or mirror, respectively. Of course, the maximum intensity or 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 Laboratoy (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.


Title:
Observation of multiple passes of electrons through thin internal targets in a betatron
Date: 2001
Publication type: Peer reviewed journal
Publication: Nucl. Instrums Methods 173, 3 (2001).
Authors: V. V. Kaplin, S. R. Uglov, O. F. Bulaev, V. J. Goncharov, M. A. Piestrup and C. K. Gary
Abstract: We present observations of the radiation produced by electrons making multiple passes through thin targets in a betatron. We show the influence of multiple passes on the distribution of electrons and on the angular distribution of bremsstrahlung. Measurements of electron-beam spots and bremsstrahlung distributions have been performed for 15–33 MeV electrons and target thicknesses of 10−5–3.5×10−3 radiation lengths. Estimates of the number of passes were obtained for thin targets by comparing them with 1.3 mm thick W and 1.5 mm thick Cu targets, through which electrons pass only once. The numbers of 33 MeV electron passes observed were 460 for 3 microns Mylar, 200 for 20 microns Be, 171 for 5 microns Cu and 30 for 15 microns Cu foils. The multiple pass effect can be useful in the future for increasing the efficiency of novel X-ray sources, such as transition and parametric radiators.


Title: A design of mammography units using a quasimonochromatic parametric x-ray source
Date:
2001
Publication type: Peer reviewed journal
Publication: Review of Scientific Instruments Vol. 72 No. 4,, 2159-2170 (2001).
Authors: M. A. Piestrup (Adelphi Technology Inc), Xizeng Wu (Department of Radiology, University of Alabama, Birmingham, Alabama 35233), V. V. Kaplin, S. R. Uglov (Nuclear Physics Institute, Tomsk Polytechnic University, P.O. Box 25, Tomsk 634050, Russia), J. T. Cremer (Adelphi Technology), D. W. Rule (Carderock Division, Naval Surface Warfare Center, 9500 MacArthur Boulevard, West Bethesda, Maryland 20817), R. B. Frioito (Department of Physics, Catholic University of America, Washington, D.C. 20064)
Abstract: In this article we present a mammography unit design using a parametric x-radiation (PXR) source. We show that PXR can provide a fanned quasimonochromatic x-ray beam that can be used to obtain mammography images of higher contrast and lower dose than those obtained from a conventional x-ray system. Changing the Bragg angle of the PXR crystal with respect to the electron beam changes the photon energy, improves image quality, and minimizes dose. Monte Carlo computer simulations are given that show that the PXR source with a 5% bandwidth gives a figure of merit close to that of the ideal monoenergetic source and significantly higher than that of the filtered-x-ray-tube sources. In order to simultaneously obtain adequate flux and achieve bandwidths below 5%, we utilized an electron-beam energy of 35 MeV and an average current of 300 μA to 1 mA for 3 s (depending upon breast thickness and density). Slits after the PX radiator are used to define both the spatial distribution and the spectral bandwidth of the x-ray beam, which is scanned over the breast in approximately 3 s. A graphite crystal C (002) in the Laue geometry is utilized as the PX radiator. Lower electron-beam currents might be possible as higher efficiency PX or hybrid radiators become available.

2000

Title: Two-dimensional x-ray focusing from compound lenses made of plastic
Date:
December 2000
Publication type: Peer reviewed journal
Publication: Review of Scientific Instruments, 71, 4375-4379 (2000).
Authors: M. A. Piestrup, H. R. Beguiristain, C. K. Gary, J. T. Cremer, and R. H. Pantell
Abstract: We have measured the intensity profile and transmission of x rays focused by a series of either spherical or parabolic lenses fabricated using Mylar(R) (C5H4O2) or Kapton(R) ~polyimide!. The use of plastics can extend the range of operation of compound refractive lenses, improving transmission and aperture size and reducing focal length. The number of unit lenses range from 193 to 600 for each compound refractive lens. Two-dimensional focusing was obtained for photon energies 8–14 keV with imaging distances of less than 1 m. For example, full-width-half-maximum linewidths down to 16 mm at a distance of only 47 cm from the lens were achieved at 9 keV. The effective apertures of the refractive lenses were measured between 250 and 364 microns with peak transmissions between 10% and 33%.


Title: Observation of bright monochromatic x-rays generated by relativistic electrons in a multilayer mirror

Date: 12 JUNE 2000
Publication type: Peer reviewed journal
Publication: APPLIED PHYSICS LETTERS VOLUME 76, NUMBER 24 pp3647-3649
Authors: V. V. Kaplin, S. R. Uglov, V.N. Zabaev, M. A. Piestrup, C. K. Gary, N. N. Nasonov, and M. J. Fuller
Abstract: We have observed the emission of 15 keV x rays produced by 500 MeV electrons passing through a x-ray multilayer mirror. The mirror consisted of 300 pairs of W and B4C layers with layer spacingof 12.36 Angstroms and supported by a 100 mm Si substrate. The x rays were emitted at the Bragg angle ug = 33.15 mrad with respect to the mirror surface and at the angle uD=66.3 mrad with respect to the electron-beam direction. The spatial distribution and the spectral angular dependence of the x rays were measured and shown to be larger than the parametric x rays emitted from the Si substrate. The value of the differential photon efficiency was estimated to be about 0.22 photons/electron/str.

1999

Title: Development of Compound Refractive Lenses for X-Rays
Date: 1999
Publication type: Conference Proceedings
Publication: Synchrotron Radiation Instrumentation - Conference proceedings, 11th US National Conference, AIP (Oct. 13-15, 1999) ed. By P. Pianetta, J. Arthur, S. Brennan, Vol. 521, 258-266.
Authors: H. R. Beguiristain, M. A. Piestrup, R. H. Pantell, C. K. Gary, J. T. Cremer, and R. Tatchyn
Abstract: One-dimensional and rotationally axisymmetric two-dimensional focusing of x-rays by plastic Compound Refractive Lens (CRL) systems are demonstrated and theoretical aspects behind the design of x-ray CRLs are presented in this report. X-rays between 8 and 19.5 keV were focused by cylindrical CRLs having focal lengths between 35 and 100 cm and fabricated using acrylic (Lucite) and polyethylene. Focusing of x-rays by a spherical CRL was also demonstrated observing a focal length of 85 cm and an effective aperture of about 320 μm for 8 keV x-rays. The gain, which is the increase in intensity in the image plane relative to the intensity that would have been obtained without a lens on that plane, was 1.5 for 8 keV photons. The gain of this spherical CRL scales about three orders of magnitude higher on undulator beam lines at third generation x-ray sources from the results obtained at the bending magnet x-ray source, with dimensions 445 microns in the vertical and 1700 microns in the horizontal, used in this work.


Title:
Cylindrical compound refractive x-ray lenses using plastic substrates
Date: September 1999
Publication type: Peer reviewed journal artucle
Publication: REVIEW OF SCIENTIFIC INSTRUMENTS VOLUME 70, NUMBER 9 SEPTEMBER 1999
Authors: J. T. Cremer, M. A. Piestrup, H. R. Beguiristain, and C. K. Gary(Adelphi Technology Inc.) R. H. Pantell
(Department of Electrical Engineering, Stanford University), R. Tatchyn (Stanford Synchrotron Radiation Laboratory, Stanford University)
Abstract: We have measured the intensity profile of x rays focused by compound refractive lenses ~CRLs! fabricated using acrylic ~Lucite! and polyethylene plastics. A linear array of closely spaced holes acts as multiple cylindrical lenses. The important parameters for this type of focusing are the focal length and absorption, and, for wavelengths shorter than 3 Angstroms, low atomic number plastics are suitable. We have experimentally demonstrated that we can achieve one-dimensional focusing for photon energies between 9 and 19.5 keV with focal lengths between 20 and 100 cm. For example, using 12 keV x rays we have achieved focal full width at half maximum linewidths down to 21 microns at a distance of only 20 cm from the CRL. The x-ray source was a synchrotron emitter whose source size in the vertical dimension was 445 microns.

1998

Title: Compact Recycled Beam Source for XRL and EUVL Exposure Tools
Date: 1998
Publication type: Conference proceedings
Publication: Emerging Lithographic Technologies, SPIE, 3331, 450 (1998).
Authors: M. A. Piestrup, M. W. Powell, J. T. Cremer, L. W. Lombardo, V.V. Kaplin, A.A. Mihal'chuk, S.R. Uglov, V.N. Zabaev, D. M. Skopik, R. M. Silzer and G. A. Retzlaff
Abstract: 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.


Title:
X-ray production simulation of an electron beam recycled through a betatrons's internal target
Date: 1998
Publication type: Peer reviewed journal
Publication: Nuc. Instrum. Methods B 145, 244-252 (1998).
Authors: V.V. Kaplin, L.W. Lombardo, A.A.Mihal'chuk, M.A. Piestrup, and S.R. Uglov
Abstract: An analysis of the circulating dynamics of 6 and 35 MeV electron beams in betatron chambers with quasi-transparent internal targets has been done by means of computer simulation. The spatial and angular distributions of the electron trajectories were studied as the electrons made multiple passes through the thin targets. The beam intensities were observed as a function of the number of passes through 0.01, 0.02, 0.05, and 0.1 mm thick silicon targets. The mean number of passes that an electron makes was determined for each combination of target thickness and beam energy. Using the data obtained from the simulation, the spectral and angular distributions of parametric X-radiation have been calculated for electrons recycled through silicon crystals.


Title:
A Transition Radiation Source with a Grazing Angle Optic for Step and Scan Lithography
Date: 1998
Publication type:
Publication:
NIMB, 145, 230-235 (1998).
Authors: M. A. Piestrup, M. W. Powell, S. Mrowka, J. T. Cremer, L. W. Lombardo, M. B. Chase, D. Snyder, H. Rietdyk and X. K. Maruyama
Abstract: Using a grazing angle mirror, the collection and collimation of transition radiation into a slit pattern that can be scanned across an image plane for X-ray dose uniformity is demonstrated. An Au-coated grazing-angle optic was used to focus transition radiation into a rectangular or slit pattern (7 mm × 16 mm) in the image plane at 631 mm from the optic and 881 mm from the transition radiator. Intensity variation across the longitudinal direction (≈10 mm) of the slit was less than ±5%. The grazing angle optic with a transition radiator can be used for step and scan lithography for obtaining circuit resolution patterns below 0.1 microns.


Title: Increased x-ray production efficiency from transition radiators utilizing a multiple-pass electron beam
Date:
June 1998
Publication type: Peer reviewed journal
Publication: REVIEW OF SCIENTIFIC INSTRUMENTS VOLUME 69, NUMBER 6 2223-2229 (1998).
Authors: M. A. Piestrup (Adelphi Technology Inc.,), L. W. Lombardo, J. T. Cremer, G. A. Retzlaff, R. M. Silzer, D. M. Skopik (Saskatchewan Accelerator Laboratory, University of Saskatchewan, 107 North Road, Saskatoon, Saskatchewan S7N 5C6, Canada)and V. V. Kaplin (Nuclear Physics Institute, Tomsk Polytechnical University, Lenin Ave. 2a, 634050 Tomsk, Russia)
Abstract: We have observed x-ray emission from transition radiators placed inside an electron storage ring. The radiators were thin (0.18–9microns) and the electrons were of sufficient energy (118–252 MeV) so that the electrons passed through the radiators many times. This effectively increased the efficiency of the radiators (photons/electron). The electron-beam lifetime in the storage ring was measured, and used to determine the number of passes through each radiator. Multiple passes between 5 and 385 were observed, thus giving a corresponding increase in radiator efficiency. Five electron-beam energies (118, 151, 181, 213, and 252 MeV) were used on a variety of radiators consisting of both single and multiple foils and different materials (C, Al, Cu, Ta). The total output power and the spatial distribution of the x rays were measured. The emission pattern was the typical annular cone of transition radiation. Single-foil transition radiation was observed whose total output power was comparable to that of multiple-foil radiators composed of the same material. Thus, for this range of parameters, the product of the number of foils times the number of passes was a constant.


Title:
X-ray emission by multiple passes of electrons through periodic and crystalline targets mounted inside a synchrotron
Date: 16 March 1998
Publication type: Peer reviewed journal
Publication: Appl. Phys. Letts. 72 pp. pp.1385-1387 (1998).
Authors: M. Yu. Andreyashkin, V.V.Kaplin, M.A.Piestrup, S.R.Uglov, V.N.Zabaev
Abstract: The number of passes of high-energy electrons through multiple foil and crystal radiators mounted inside of the Tomsk "Sirius" synchrotron, and the resulting increase in x-ray production efficiencies from these radiators, have been measured. The influence of electron transmission on the spectral and spatial distributions of parametric x radiation and on the spatial distribution of transition radiation has also been observed. We find that multiple passes increase the yields of these sources without destroying their angular distributions and spectra. Thus, multiple passes of electrons through these novel radiators may make them useful as x-ray sources for scientific and industrial purposes.

1997

Title: A Single-Stepper Soft-X-Ray Source for Step-and-Scan Tools
Date:
1997
Publication type: Conference proceedings
Publication: SPIE 3048, pp. 176-182 (1997).
Authors: Melvin A. Piestrup, Michael W. Powell, Stanley Mrowka, Louis W. Lombardo, Michael B. Chase, J. Theodore Cremer, and Xavier K. Maruyama
Abstract: 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%.

1996

Title: Multilayer Optics for Harmonic Control of Angiography Beam Line Sources
Date: 1996
Publication type: Peer reviewed journal
Publication: Rev. Sci. Instrum., 67, 1-5 (1996).
Authors: R. Tatchyn, T. Cremer, D. Boyers, Q. Li, M. Piestrup
Abstract: In recent work, multilayers with band‐tailored optics for dual energy digital subtraction angiography (DDSA) applications have been designed and tested at SSRL. Control of various multilayer parameters, including period grading, ratio of high‐to‐low Z material thickness, number of layers, etc., was used to produce reflectors with bandwidths ranging from 0.6%–10% and efficiencies in the 30%–95% range. In this paper, we consider the control of multilayer bandshapes and the implementation of double‐reflection multilayer configurations to further control the first harmonic (33 keV) bandwidth and to suppress or eliminate the 66 keV and 99 keV harmonics present on angiography beamlines driven by wiggler or micropole undulator sources.


Title:
Alternative source for step and scan lithography
Date: 1996
Publication type: Conference proceedings
Publication: SPIE 2723, 288 (1996).
Authors: M. A. Piestrup, M. W. Powell, L. W. Lombardo
Abstract: In recent work, multilayers with band‐tailored optics for dual energy digital subtraction angiography (DDSA) applications have been designed and tested at SSRL. Control of various multilayer parameters, including period grading, ratio of high‐to‐low Z material thickness, number of layers, etc., was used to produce reflectors with bandwidths ranging from 0.6%–10% and efficiencies in the 30%–95% range. In this paper, we consider the control of multilayer bandshapes and the implementation of double‐reflection multilayer configurations to further control the first harmonic (33 keV) bandwidth and to suppress or eliminate the 66 keV and 99 keV harmonics present on angiography beamlines driven by wiggler or micropole undulator sources

1995

Title: Polarized Angular Distributions of Parametric X-radiation and VUV Transition Radiation from Relativistic Electrons
Date:
1995
Publication type:
Publication:
Phys. Rev. E. Rapid Communication Vol. 51, R2759-R2762 April (1995).
Authors: R. B. Fiorito, D. W. Rule, M. A. Piestrup, X. K. Maruyama, R. M. Silzer and D.M. Skopik
Abstract: We present quantifiable images of the angular distributions (AD's) of parametric x radiation (PXR), and vacuum-ultraviolet transition radiation (vuv TR) from 230 MeV electrons interacting with a silicon crystal. Both AD's are highly polarized. The vuv TR and optical TR data provide measurements of the beam energy and effective divergence angle. Using these quantities and separately known values of the electronic susceptibility ‖χ0‖, we show that the measured PXR AD is in good agreement with the predictions of single crystal theory. Our analysis suggests a method to measure ‖χ0‖ using PXR AD's.

1994

Title: Tests of variable-band multilayers designed for investigating optimal signal-to-noise vs. artifact signal ratios in dual-energy subtraction angiography (DDSA) imaging systems
Date:
1994
Publication type: Peer reviewed journal
Publication: Nuclear Instrum. and Methods, A 346 pp. 565-570 (1994).
Authors: D. Boyers, A. Ho, Q. Li, M. Piestrup, M. Rice, R. Tatchyn
Abstract: In recent work, various design techniques were applied to investigate the feasibility of controlling the bandwidth and bandshape profiles of tungsten/boron-carbon (W/B4C) and tungsten/silicon (W/Si) multilayers for optimizing their performance in synchrotron radiation based angiographical imaging systems at 33 keV. Varied parameters included alternative spacing geometries, material thickness ratios, and numbers of layer pairs. Planar optics with nominal design reflectivities of 30–94% and bandwidths ranging from 0.6–10% were designed at the Stanford Synchrotron Radiation Laboratory, fabricated by the Ovonic Synthetic Materials Company, and characterized on Beam Line 4-3 at the Stanford Synchrotron Radiation Laboratory. In this paper we report selected results of these tests and review the possible use of the multilayers for determining optimal signal to noise vs artifact signal ratios in practical dual-energy digital subtraction angiography systems.

1993

Title: Surface roughness effects on cylindrical grazing incidence x-ray optics for transition radiation
Date: 1993
Publication type: Peer reviewed journal
Publication: J. Appl. Phys. 74, 5320-5326 (1993).
Authors: H. Ho, M. A. Piestrup, R. M. Silzer, and D. M. Skopik
Abstract: Quartz and nickel cylinders were used as grazing incidence x‐ray optics for transition radiation (TR) from Al, Ti, and Cu foil stacks. The cylinders were used to direct the otherwise diverging TR to a small spot (1 mm diameter), with measured fluxes of up to 330 W/A cm2 averaged over the spot area. Computer simulations were performed and compared to the measured results. It was found that including surface roughness effects in the form of a Debye–Waller reduction factor on the reflectivity was necessary to get good agreement between the simulations and experimental results in certain cases, but not in others. A simple heuristic model which can be used to determine when roughness effects are important is presented. Use of this model in conjunction with the computer simulations accurately predicts the measured results, and further suggests the use of different optic materials at different x‐ray wavelengths.


Title: Noninvasive digital subtraction angiography with a channeling radiation x-ray source

Date: 1993
Publication type:
Publication:
Medical Physics 20, 1527 (1993).
Authors: C.K. Gary, M.A. Piestrup, D.G. Boyers, C.I. Pincus, R.H. Pantell, and G.B. Rothbart
Abstract: Channeling radiation could provide a viable source for digital energy subtraction angiography (DESA). A signal to noise ratio (SNR) of 6.2 for a resolution of 0.5 mm×0.5 mm could be achieved using a 6‐mA 100‐ms 20‐MeV electron‐beam pulse and a diamond channeling crystal as the x‐ray source. This article investigates the choice of a DESA contrast agent and the parameters of a channeling‐radiation x‐ray source to develop a channeling‐radiation DESA imaging system. The production of dual‐energy peaks, the maximum available x‐ray flux, the advantages of an area exposure, the necessity of a mosaic Bragg‐crystal filter to reduce patient dose, the optimal energy separation of the peaks for a quasimonochromatic x‐ray source, and the reduction of the signal from bone are discussed, leading to estimated SNRs and image resolution for a channeling‐radiation imaging system. The computer analysis developed to calculate the image quality is also discussed.


Title: Parametric X-ray Generation from Moderate Energy Electron Beams

Date: 1993
Publication:
Nucl. Instrum. and Methods, B79, 758-761 (1993)
Authors: R. B. Fiorito, D. W. Rule, M. A. Piestrup, Qiang Li, A. H. Ho, X. K. Maruyama
Abstract: We have examined parametric X-ray radiation (PXR) as a low cost, pulsed, tuneable X-ray source. In contrast to synchrotron radiation (SR), PXR requires only moderate beam energies produced by conventional linear accelerators. We have determined the maximum PXR intensity that can be achieved from simple crystals placed in a high current, relativistic electron beam. PXR compares favorably to SR on a per electron and pulsed basis. Our calculations and experiments indicate that PXR is a useful source for applications requiring X-rays with energies of a few keV to several tens of keV. For example, we have shown that a PXR source is a viable alternative to SR for digital subtraction angiography based on tuning about the 33 keV iodine K-edge.


Title: Observation of Higher Order Parametric X-ray Spectra in Mosaic Graphite and Single Silicon Crystals

Date: 1993
Publication type:
Publication:
Phys. Rev. Lett. 71, 704-707 (1993).
Authors: R. B. Fiorito, D. W. Rule, X. K. Maruyama, K. DiNova, M. J. Osborne, S. Evertson, D. Snyder, H. Rietdyk, M. A. Piestrup, and A. H. Ho
Abstract: We have observed up to 8 orders (n) in the spectra of parametric x-radiation (PXR) in the range 5–40 keV, produced by the interaction of a 90 MeV electron beam with mosaic graphite and single silicon crystals. The measured yields and intensity ratios, I(n≥2)/I(n=1), in graphite are not in agreement with the theory of PXR for mosaic crystals. In comparison, the ratios of intensities in silicon are close to the predictions of PXR theory for perfect crystals. The bandwidths of spectral lines measured in both silicon and graphite are in good agreement with theoretical predictions.

1992

Title: Measurements of x-ray emission from zinc and molybdenum transition radiators
Date: 1992
Publication type:
Publication:
J. Appl. Phys. 73, 5152-5157 (1992)
Authors: M. A. Piestrup, A. H. Ho, Qiang Li, R. M. Silzer, G. Feldman, D.M. Skopik


Title: Observation of the focusing of x-ray transition radiation using cylindrical optics

Date: 1992
Publication type:
Publication:
Appl. Phys. Lett. 61, 1019-1021 (1992).
Authors: M. A. Piestrup, D. G. Boyers, C. I. Pincus, Qiang Li, A. H. Ho (Adelphi Technology Inc), X. K. Maruyama, D. D. Snyder (Naval Postgraduate School, Monterey, Cahfornia 93943 ), D. M. Skopik, R. M. Silzer (Saskatchewan Accelerator Laboratory, University of Saskatchewan, Saskatoon, Saskatchewan S7N 0 WO, Canada ), M. J. Moran (Lawrence Livermore National Laboratory, University of Caltfornia, Livermore, Caltfornia 94550) and G. B. Rothbart (Software Science Inc., 1)
Abstract: We have measured the profile of x rays generated by a transition radiator and focused by simple cylindrical optics. Soft x rays with photon energies between 1 and 4 keV were generated by a 93-MeV electron beam striking a stack of eight foils of 3.5,micron-thick mylar. These x rays were emitted in an annular cone and were collected by a quartz cylinder which focused the x rays to a OS-mm-diam spot at a distance of 1.35 m from the transition radiator.


Title: Measurement of x-ray emission from photo-absorption-edge transition radiation

Date: 1992
Publication type:
Publication:
J. Appl. Phys. 72, 4300-4307(1992).
Authors: I. Pincus, M. A. Piestrup, D. G. Boyers, J. L. Harris, D. M. Skopik, R. M. Silzer, H. S. Caplan, X. K. Maruyama, and G. B. Rothbart
Abstract: This article describes the measurements of x‐ray power, spatial and spectral distributions from transition radiators whose spectra are narrowed by the foil material's K‐shell photoabsorption edge. We used two foil stacks, one composed of 15 foils of 3‐μm‐thick Zn and the other composed of 15 foils of 4‐μm‐thick Mo. At low average currents, the x‐ray spectrum produced by transition radiation was measured by pulse height analysis to be between 5 and 9.7 keV for the Zn radiator and between 10 and 20.0 keV for the Mo radiator. These measurements compared well with calculations. The x‐ray spatial distribution from the Zn radiator was measured using a silicon linear diode array. The x rays generated by the Zn radiator were found to be emitted in a forward‐directed cone with half angle of ∼1.9 mrad with the center of the expected annulus filled. The power density in the peak of the annulus was found to be 50 mW/(mA cm2). At a high average electron‐beam current of 12.5 μA, the x‐ray power produced by a stack of ten Zn foils was measured in the spectral range between 5 and 9.66 keV to be 1.54 mW with the peak power in the 1 μs macropulse to be 8.5 W. Electron‐beam energies between 249 and 282 MeV were used in these experiments.  

1991

Title: The optimization of channeling radiation source crystals to produe intense quasimonochromatic x rays
Date:
1991
Publication type:
Publication:
J. Appl. Phys. 70, 2995-3002 (1991).
Authors: C.K. Gary, R.H. Pantell, M. Ozcan, M.A. Piestrup, and D.G. Boyers
Abstract: Channeling radiation is a source of intense, tunable, quasimonochromatic x rays produced by electrons traveling along a direction of symmetry through a crystal. We analyze the effect of the channeling source crystal, through both its composition and lattice structure, on the number of photons emitted per electron, the linewidths of the radiation, and the maximum sustainable currents to identify the crystal which will yield the most photons in a bandwidth of less than 10% full width at half maximum (FWHM). Although high atomic number (Z) crystals produce a greater number of photons per electron, given their poor thermal properties these crystals cannot sustain as high average currents as lower Z crystals. The linewidths of the channeling radiation emitted from high Z crystals are as large as 50% FWHM, and electrons are dechanneled more quickly in these crystals, limiting their use as a quasimonochromatic x‐ray source. Given its exceptional thermal conductivity and narrow linewidths, diamond is the optimal source crystal for the production of intense, quasimonochromatic x rays using channeling radiation.


Title: Beryllium-foil transition radiation source for x-ray lithography
Date:
1991
Publication type:
Publication:
Appl. Phys. Lett. 59, 189 (1991).
Authors: M.A. Piestrup, D.G. Boyers, C.I. Pincus, J.L. Harris, R.M. Silzer, D.M. Skopik
Abstract: We have measured the total soft‐x‐ray power from a transition radiator composed of a stack of 25 beryllium foils each 1.0 μm thick which were penetrated by a relativistic electron beam whose maximum power was approximately 7 kW. The maximum total soft‐x‐ray power was measured to be 15.2 mW for a 245 MeV, 37 μA electron beam. The bandwith of the radiation at the full width half maximum points was calculated to be between 0.6 and 1.6 keV. In addition, we have exposed photoresist‐coated silicon wafers at a distance of 3 m from the radiator. Exposure times of the bare resist were as short as 120 s for 5 cm2 of wafer are (resist sensitivity is 55.6 mJ/cm2). The shortest time for mask/wafer exposure was 180 s for 5 cm2.

1990

Title: Channeling of electrons in Si produces intense quasimonochromatic, tunable, picosecond x-ray bursts
Date:
1990
Publication type:
Publication:
Phys. Rev. B 42, 7-14 (1990).
Authors: C.K. Gary, A.S. Fisher, R.H. Pantell, J. Harris and M.A. Piestrup
Abstract: We report the results of channeling-radiation experiments performed with high-current electron beams. The research shows that electron channeling can produce a useful source of hard x rays that is highly directional, polarized, intense, tunable, with a 10–15 % linewidth, and of picosecond duration. On a picosecond time scale, using a 30-MeV electron beam with a peak current of 50 A channeled in Si, photon fluxes of 1.0×1019 photons/(sr keV sec) have been measured at a wavelength of 0.42 Angstroms