Carl Tillman

Lund University, Lund, Skåne, Sweden

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Publications (9)28.77 Total impact

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    ABSTRACT: To determine whether intense laser-produced x rays have an increased radiation hazard. Mammalian cells were exposed to x rays from a laser-produced plasma that produced ultrahigh peak absorbed dose rates, up to a factor of 10(10) higher than those produced by conventional x rays used in imaging. The cell survival was studied as a function of the absorbed dose. The survival of mammalian cells exposed to high peak absorbed dose rates with laser-produced x rays was compared with the survival of cells exposed to standard absorbed dose rates with conventional x-ray sources. Comparative survival studies were performed by using a conventional x-ray tube and a cobalt 60 source. The absorbed doses in the irradiation field were measured with thermoluminescent dosimeters. Cell survival following irradiation by filtered, laser-produced x rays with a high dose rate was not markedly different from the survival following irradiation by conventional sources. There was, however, a notable difference between the survival after exposure to filtered, laser-produced x rays and the survival after exposure to unfiltered laser-produced x rays. Exposure to filtered, laser-produced x rays with a high dose rate does not lead to increased harm to mammalian cells exposed in vitro compared with the harm from exposure to x rays from conventional sources, which indicates that the use of high-power laser facilities for medical imaging is justified.
    Preview · Article · Jan 2000 · Radiology
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    ABSTRACT: X-rays from a laser-produced plasma were analysed using single-photon counting germanium detectors. Special attention was given to the extremely high photon flux, requiring either a long source-detector distance and narrow collimated measurement geometry in order to avoid severe pile-up of pulses in the spectrometer, or the use of a Compton scattering geometry. With the use of these techniques, individual characteristic K-lines were resolved for the first time. Efficiencies for the conversion of the laser light into X-rays were determined, being up to 10−4 for Bremsstrahlung, and up to 10−5 for the characteristic K-line emission. Electron temperatures of ∼100 keV were assessed.
    No preview · Article · Jul 1997 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: The authors evaluate the feasibility of differential imaging of contrast media, with division of individual pixel values obtained from digital images generated by characteristic radiation from a laser-produced plasma, bridging the K-absorption edge of the contrast agent. Laser pulses from an ultrashort-pulse terawatt laser system were focused onto gadolinium and tantalum targets, creating a plasma from which characteristic radiation and Bremsstrahlung was emitted. The elements of the target were selected so the characteristic emission lines of one of the elements were below the K edge of the contrast agent and the emission lines of the other element above. A phantom with gadolinium and other elements in various concentrations was examined. One radiographic exposure was made using a gadolinium target source and a subsequent exposure using a tantalum source. Both images were recorded digitally and the transmission ratios calculated by division of the individual pixel values. When viewed separately, the two images of the test phantom appeared similar. In the differential image, only the gadolinium solutions were bright, reflecting a difference in attenuation between the two exposures. Element-specific radiographs can be obtained by differential imaging. When fully explored, the technique may allow for contrast-enhanced radiography with increased sensitivity and decreased contrast dose.
    No preview · Article · Jun 1997 · Investigative Radiology
  • G Hölzer · E Förster · M Grätz · C Tillman · S Svanberg
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    ABSTRACT: The interaction of a sub-picosecond (sub-ps) laser with a high-Z target produces a hard x-ray continuum, but to our knowledge no high-resolution study of the line emission is known. We present here crystal spectroscopy as a tool for the observation of energetic line x-radiation from a sub-ps laser-produced plasma. Reflection properties of flat and bent crystals for x-ray spectroscopy are analyzed theoretically for both the Bragg and the Laue geometries and optimized for a crystal spectroscopy of hard (>50 keV) x-radiation. The crystal setup is optimized for spectroscopic applications with regard to high throughput and spectral resolution. The characteristic tantalum Kα,β- and Lα,β-line emissions from a sub-ps laser-produced plasma is observed for the first time. A resolving power of about 450 is achieved which is much higher than that for comparable absorption filter techniques (E/ΔE ≈ 15).
    No preview · Article · Mar 1997 · Journal of X-Ray Science and Technology
  • Matthias Grätz · Carl Tillman · Ian Mercer · Sune Svanberg
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    ABSTRACT: We present investigations on the generation of X-ray radiation suitable for different types of medical imaging. Pulses from a 10 Hz terawatt laser system with a duration of 150 fs are focused onto a solid high-Z material target, with focal spot intensities reaching 1018 W/cm2. The produced plasma emits broadband X-ray radiation with photon energies up to the MeV region. The application of this X-ray radiation offers new features for medical radiography. Our source allows magnification imaging as well as ultrashort single-shot exposures. New contrast imaging techniques making use of an enhanced characteristic line emission are investigated. The experimental set-up also allows the study of ablation phenomena from sub-picosecond laser pulses by means of particle deposition on thin glass plates. Deposition patterns were studied dependent on different plasma-generation parameters.
    No preview · Article · Apr 1996 · Applied Surface Science
  • C. Tillman · I. Mercer · S. Svanberg · K. Herrlin
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    ABSTRACT: We demonstrate the novel application of hard x rays emitted by a laser-produced plasma for differential imaging of elements. An x-ray-emitting laser-produced plasma, obtained by the focusing of radiation from a 10-Hz terawatt laser, is used for biological imaging. The x-ray source can be arranged to yield characteristic x-ray emission lines with photon energies that bridge the K absorption edge of a chosen atomic species. One can obtain element-specific radiographs by recording transillumination images for different target materials on digital image plates and by subsequently subtracting or dividing the images. Successful phantom and experimental animal imaging are performed utilizing tantalum and gadolinium as target materials for the terawatt laser and gadolinium as the imaged contrast agent.
    No preview · Article · Jan 1996 · Journal of the Optical Society of America B
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    ABSTRACT: Imaging of technical and biological objects using hard X-rays from a laser-produced plasma source is demonstrated. Magnification radiography and single-shot imaging of biological samples are feasible with the source, which utilised focused radiation from a short-pulse terawatt laser. Differential imaging with element specificity and a new projection geometry for X-ray radiography are proposed.
    No preview · Article · Sep 1995 · Applied Physics B
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    ABSTRACT: Observations of harmonic generation from solid Al targets irradiated at intensities of 1017 W/cm2 using a tabletop Ti:sapphire terawatt laser system are reported. For irradiances with laser light at a wavelength of λ = 794nm (the fundamental frequency), harmonics up to the 7th, while for irradiances with frequency doubled laser light (λ = 397) nm harmonics up to the 4th of the respective incident radiation were detected.
    No preview · Article · Jun 1995 · Optics Communications
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    ABSTRACT: To evaluate the use of x-ray imaging performed with a high-power laser system in biologic and medical studies. A compact terawatt laser system based on chirped pulse amplification in titanium-doped sapphire was used. X rays were generated by irradiating a high-atomic-number target (tantalum). When photons with an energy below 10 keV were removed with use of 3 mm of aluminum, the half-value layer in aluminum for the remaining x rays was approximately 10 mm. The x-ray source allowed performance of biologic magnification radiography. Star-pattern tests indicated an equivalent focal spot size of less than 60 microns. Exposures of a single pulse could be obtained. The duration of a single x-ray pulse was estimated to be of the order of picoseconds. With use of subpicosecond laser pulses, x-ray generation can occur with a smaller equivalent focal spot size than with conventional x-ray sources.
    No preview · Article · Nov 1993 · Radiology