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  • 78.47.+p  (2)
  • Spatial resolution  (2)
  • 07.20.−n  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Does femtosecond time-resolved second-harmonic generation probe electron temperatures at surfaces? (1996)
    Springer
    Applied physics 63 (1996), S. 541-544 
    Details
    ISSN: 1432-0649
    Keywords: 42.65.Ky ; 78.47.+p ; 63.20.Kr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Femtosecond pump-probe second-harmonic generation (SHG) and transient linear reflectivity measurements were carried out on polycrystalline Cu, Ag and An in air to analyze whether the electron temperature affects Fresnel factors or nonlinear susceptibilities, or both. Sensitivity to electron temperatures was attained by using photon energies near the interband transition threshold. We find that the nonlinear susceptibility carries the electron temperature dependence in case of Ag and Au, while for Cu the dependence is in the Fresnel factors. This contrasting behavior emphasizes that SHG is nota priori sensitive to electron dynamics at surfaces or interfaces, notwithstanding its cause.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01828954
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Femtosecond time-resolved reflection second-harmonic generation on polycrystalline copper (1995)
    Springer
    Applied physics 60 (1995), S. 137-142 
    Details
    ISSN: 1432-0630
    Keywords: 142.65.Ky ; 63.20.Kr ; 78.47.+p
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Optical Second-Harmonic Generation (SHG) in reflection from a polycrystalline copper surface in air was studied using femtosecond time-resolved pump and probe measurements at λ=625 nm. The observed time dependence of second-harmonic yield from the probe beam demonstrates, that SHG is a very sensitive technique for measuring transient electron temperatures of metals even when these are covered by an oxide layer. For polycrystalline copper, an electron-phonon energy transfer time of 2 ps was observed, corresponding to a coupling constant of 3.75×1017 W/m3 K at average lattice temperatures of about 500 K. The analysis of experimental data indicates that the time dependence of SHG is governed by the linear dielectric function ε which, in turn, is affected by the electron temperature. There is no evidence for a temperature dependence of the nonlinear susceptibility χ(2).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01538238
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Transient thermal gratings at surfaces for thermal characterization of bulk materials and thin films (1995)
    Springer
    Applied physics 61 (1995), S. 253-261 
    Details
    ISSN: 1432-0630
    Keywords: 07.20.−n ; 44.10.+i ; 44.30.+v
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Transient Thermal Gratings (TTGs) at surfaces of absorbing materials have been utilized for investigating heat diffusion in bulk materials and thin films. In this report, we describe the theoretical background of the technique and present experimental data. TTGs were excited in the surface plane by interference of two pulsed laser beams and monitored by a cw probe beam, either via temperature dependence of the reflectivity or by deflection from the displacement pattern. A theoretical model describing the thermal and thermoelastic surface response was developed, both for a homogeneous material and a multilayer structure. The potential of the technique will be demonstrated by experimental results on (i) thermal diffusivities of bulk materials, (ii) anisotropic lateral heat transport, and (iii) thermal diffusivities of metal and diamond films. Furthermore, we will show that TTGs allow thermal depth profiling of inhomogeneous materials whenever there is a vertical gradient in thermal conductivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01538190
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Use of scanner characteristics in iterative image reconstruction for high-resolution positron emission tomography studies of small animals (1997)
    Springer
    European journal of nuclear medicine 24 (1997), S. 779-786 
    Details
    ISSN: 1619-7089
    Keywords: Key words: Positron emission tomography ; Spatial resolution ; Image restoration ; Animal studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract. The purpose of this work was to improve of the spatial resolution of a whole-body positron emission tomography (PET) system for experimental studies of small animals by incorporation of scanner characteristics into the process of iterative image reconstruction. The image-forming characteristics of the PET camera were characterized by a spatially variant line-spread function (LSF), which was determined from 49 activated copper-64 line sources positioned over a field of view (FOV) of 21.0 cm. This information was used to model the image degradation process. During the course of iterative image reconstruction, the forward projection of the estimated image was blurred with the LSF at each iteration step before the estimated projections were compared with the measured projections. The imaging characteristics of the high-resolution algorithm were investigated in phantom experiments. Moreover, imaging studies of a rat and two nude mice were performed to evaluate the imaging properties of our approach in vivo. The spatial resolution of the scanner perpendicular to the direction of projection could be approximated by a one-dimensional Gaussian-shaped LSF with a full-width at half-maximum increasing from 6.5 mm at the centre to 6.7 mm at a radial distance of 10.5 cm. The incorporation of this blurring kernel into the iteration formula resulted in a significantly improved spatial resolution of about 3.9 mm over the examined FOV. As demonstrated by the phantom and the animal experiments, the high-resolution algorithm not only led to a better contrast resolution in the reconstructed emission scans but also improved the accuracy for quantitating activity concentrations in small tissue structures without leading to an amplification of image noise or image mottle. The presented data-handling strategy incorporates the image restoration step directly into the process of algebraic image reconstruction and obviates the need for ill-conditioned ”deconvolution” procedures to be performed on the projections or on the reconstructed image. In our experience, the proposed algorithm is of special interest in experimental studies of small animals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879667
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    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Use of scanner characteristics in iterative image reconstruction for high-resolution positron emission tomography studies of small animals (1997)
    Springer
    European journal of nuclear medicine 24 (1997), S. 779-786 
    Details
    ISSN: 1619-7089
    Keywords: Positron emission tomography ; Spatial resolution ; Image restoration ; Animal studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The purpose of this work was to improve of the spatial resolution of a whole-body positron emission tomography (PET) system for experimental studies of small animals by incorporation of scanner characteristics into the process of iterative image reconstruction. The image-forming characteristics of the PET camera were characterized by a spatially variant line-spread function (LSF), which was determined from 49 activated copper-64 line sources positioned over a field of view (FOV) of 21.0 cm. This information was used to model the image degradation process. During the course of iterative image reconstruction, the forward projection of the estimated image was blurred with the LSF at each iteration step before the estimated projections were compared with the measured projections. The imaging characteristics of the high-resolution algorithm were investigated in phantom experiments. Moreover, imaging studies of a rat and two nude mice were performed to evaluate the imaging properties of our approach in vivo. The spatial resolution of the scanner perpendicular to the direction of projection could be approximated by a one-dimensional Gaussian-shaped LSF with a full-width at half-maximum increasing from 6.5 mm at the centre to 6.7 mm at a radial distance of 10.5 cm. The incorporation of this blurring kernel into the iteration formula resulted in a significantly improved spatial resolution of about 3.9 mm over the examined FOV As demonstrated by the phantom and the animal experiments, the high-resolution algorithm not only led to a better contrast resolution in the reconstructed emission scans but also improved the accuracy for quantitating activity concentrations in small tissue structures without leading to an amplification of image noise or image mottle. The presented data-handling strategy incorporates the image restoration step directly into the process of algebraic image reconstruction and obviates the need for ill-conditioned ”deconvolution“ procedures to be performed on the projections or on the reconstructed image. In our experience, the proposed algorithm is of special interest in experimental studies of small animals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879667
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
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