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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 4823-4829 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Calculations of focus characteristics for x-ray focusing systems using either flat or bent crystals with two-dimensional modulated surfaces are presented. Based on the wave-optics approach, the analytical formulas are derived for elliptical Fresnel zone structures (flat crystals) and linear Bragg zone structures (toroidally bent crystals). It is shown that for a given Si(111) reflection and Ti Kα radiation, a micron-size focal spot can be achieved by using only one flat crystal with a modulated surface. The peak intensity is then nearly 100 times higher than that of the flat crystal without modulations. However, for a toroidally bent crystal with both Fresnel and Bragg diffraction amplitudes, the latter becomes dominant, since, due to the bending, the rapid oscillations of the Fresnel diffraction amplitude vanish. It is also shown that a focal spot of 0.3 μm for a bent crystal with linear Bragg zone structures is approximately four times narrower than that of an unmodulated surface. From the analysis, the modulated surfaces for cylindrically and spherically bent crystals are deduced to be a combination of Bragg and Fresnel zones. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1849-1854 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Calculations and analysis of an extended x-ray source image with a 2D focusing geometry are presented. Based upon the calculations for an x-ray point source image (Paper Ia), theoretical expressions are derived which reveal the contributions from both the Bragg and the optical (Fresnel) diffractions to the intensity distribution of the image at the focal plane. That is, for a given focusing geometry, the intensity distribution of the image of an extended source consists not only of the crystal rocking curves for a bent crystal, due to the Bragg diffraction; but also of the optical diffraction, the Fresnel integral, due to the phase correlations of the thickness and the spatial extent of a doubly bent crystal. The contribution from the optical diffraction depends solely upon the bent crystal focusing geometry. The relationship between the source and the image at the focal plane is obtained, and the intensity distribution of an extended x-ray source image with a 2D bent silicon crystal is given. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1843-1848 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A wave optics approach to the calculations of the intensity distribution of an x-ray point source image with a two-dimensional (2D) focusing geometry is presented. Analytical formulas are derived to calculate the intensity distribution at the focal plane. This approach has taken into account the effects of x-ray scattering within a 2D bent crystal, which includes the x-ray refraction and absorption inside the crystal, and the effects of elastically deformed crystals described by the anisotropic elasticity theory. Based upon the elastic bending model, the modified Bragg law and 2D lens equations are discussed. In addition, the x-ray extinction distance for curved crystals is found to be dependent on the size and the bending radius of bent crystals. For a monochromatic x-ray point source, calculation of the intensity distribution with a 2D bent silicon crystal is given for both perfect and misaligned sources. The spatial resolution and the size of the image are determined. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 3048-3056 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A monochromator has been developed for coronary angiography, comprising a single bent crystal of silicon in Laue transmission geometry. K spectra of laser irradiated solid tin and tantalum (Z=50 and 73, respectively) targets were measured. The high resolution crystal spectrometer resolve the Sn and Ta Kα doublets, allowing in a proof-of-principle experiment the absolute Kα photon numbers emitted by the source to be determined. The Ta Kα yield is measured as a function of the laser pulse energy, allowing an assessment to be made of the suitability of such sources for medical applications. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1288-1299 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: An effective x-ray optical method to focus keV x-ray pulses shorter than one picosecond by using spherically or toroidally bent crystals is presented. The spectral, spatial, and time-dependent properties of focusing by two-dimensional bent crystals are calculated by considering geometrical effects, physical limitation in high performance crystal optics, and reflectivities obtained by x-ray diffraction theory. These properties are compared with first experimental results of focusing x rays from a plasma created by a laser pulse with 4.5 mJ energy and 100 fs pulse length. The x-ray signals, simultaneously obtained from a von Hámos spectrometer and two-dimensional bent crystals are compared and found in good agreement with theoretical data. The possibilities and aspects of laser pump x-ray probe experiments using this type of x-ray optics system and currently available laser systems are discussed. © 1999 American Institute of Physics.
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  • 6
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We report the first use of toroidally bent crystals to record two-dimensional, spatially resolved, monochromatic images of laser-produced fusion plasma. The electron temperature was determined by seeding the deuterium fuel with argon and evaluating the intensity ratio of the two monochromatic images in the Ar+ 17Ly β and the Ar+ 16He β lines. Silicon and germanium crystals were chosen to achieve high diffraction reflectivities. Spatial resolution better than 10 μm was achieved by bending the crystals toroidally to minimize the geometrical aberrations [E. Förster, K. Gäbel, and I. Uschmann, Laser Particle Beams 9, 135 (1991)]. Comparison of the two line intensities requires a calibrated imaging system. Monochromatic images of fusion pellets driven with the GEKKO XII glass laser system are presented. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 26-30 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A double-crystal x-ray spectrometer (DCS) has been used to obtain high-resolution x-ray spectra of laser-produced plasmas. The DCS has a high dispersion, and thus can obtain highly resolved spectra in circumstances where the resolution of a conventional single-crystal Bragg spectrometer at comparable source-to-detector distances would be limited by the source size. In addition the DCS also yields unit-magnification one-dimensional spatial resolution in the direction perpendicular to the spectral direction. The instrument produces two spectra symmetrically disposed about a central wavelength, which makes it especially useful for measuring spectral line shifts. Analysis of the spectra from hydrogenic aluminium and helium-like chlorine indicates a resolving power (λ/Δλ) greater than 2500 and a spatial resolution better than 30 μm.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3669-3675 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We have constructed a quasimonolithic crystal consisting of two offset, parallel-mounted quartz (101¯0) crystals for determining the wavelengths of x-ray transitions on an absolute scale without the need for reference lines. The design and organization of the quasimonolith crystal device, as well as the determination of the relevant parameters and their corresponding uncertainties are discussed. A calibration chain is established that enables linking any wavelength measurement directly to optical wavelength standards and thus to SI units. Our analysis shows that absolute wavelength measurements with an uncertainty of one part per million are in principle possible with the device. Implementation of the quartz quasimonolith in a high-resolution vacuum spectrometer used to study x-ray line emission from an electron beam ion trap is described. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 3234-3243 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A vertical dispersion variant of the double-crystal spectrometer (DCV), which has been successfully used to study radiative transport in plasmas with large velocity gradients, is described. The full theory of the instrument is presented with particular reference to distortion of the spectral lines observed. The main characteristics of the DCV were computed by ray tracing procedures and compared with experiment. Due to its extremely high dispersion, the DCV minimizes geometric apparatus smearing, the distortion of the spectra is negligible a high spectral resolution (typically several thousand or better) can be achieved at relatively small source-to-detector distances. The instrument provides two sets of spectra with one-dimensional spatial resolution at the level of 10 μm, and its sensitivity to relative positions and shifts of the spectral lines may be estimated as one part in 105. The very high precision in wavelength determination, both absolute and relative, combined with an acceptable luminosity make this spectrometer especially useful for ultrahigh-resolution spectroscopy of laser-produced plasmas. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5012-5016 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A special crystal monolith was fabricated for absolute measurements of x-ray wavelength. It consists of two flat quartz plates, accurately cut relative to reflecting net planes, with a fixed distance between them. Absolute wavelengths (i.e., without use of reference lines) of L-shell laser produced spectra of Cu, Ge, As, etc. have been measured in the 7.5–8.5 A(ring) with an accuracy of Δλ/λ=10−5. Our Johann type x-ray spectrometer with a cylindrically bent quartz has been used to reveal line coincidences necessary for photopumping processes. In this scheme source-size influences are smaller, therefore, line profiles have been measured at a spectrometer resolution better than 5000. Because of its focusing in the sagittal plane, a von Hámos type x-ray spectrometer has been used to detect the small x-ray emission of subpicosecond laser-produced plasmas (E=2 mJ, t=100 fs). X-ray spectra of Al both Kα, Kβ lines and Heα-resonance line with its satellites. Finally, a multichannel x-ray microscope has been designed and fabricated. It consists of several two-dimensionally bent crystals where each of them images one x-ray line emitted by a laser-produced plasma. The spatial resolution of x-ray line images is about 5 μm, and the width of the spectral ranges is Δλ/λ=10−4 to 10−2. Thus, the spatial distribution of ions radiating in selected x-ray lines have been found being of interest in the study of population inversions.
    Materialart: Digitale Medien
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