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  • 1
    Electronic Resource
    Electronic Resource
    A 4×1 GHz Array Acousto-Optical Spectrometer (1999)
    Springer
    Experimental astronomy 9 (1999), S. 17-38 
    Details
    ISSN: 1572-9508
    Keywords: Radio Astronomy ; Array Systems ; Acousto-Optical Spectrometer ; Back-ends ; Radiometers ; Heterodyne Instrumentation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper an array acousto-optical spectrometer (AOS) with four 1 GHz bands and a frequency channel spacing of 1 MHz is presented. A discussion about the requirements which have to be fulfilled by the presented instrument for applications in radio astronomy is given as well as e detailed description of the optical design. Remarkable test results have been achieved such as an Allan-Variance minimum time of about 1000 s, identical noise performance, and identical frequency calibration of all bands. The reproducibility of measurements has been demonstrated by tests with CH3CN, using an absorption cell. The question of the maximum number of bands per array AOS is discussed. Although it may seem promising to increase the number of bands per optical unit to e.g. eight or more instead of four, a strong limitation has been found due to the increasing r.f. power level on the Bragg cell which affects the baselines of the spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008093310165
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Phase gratings in the visible and near-infrared spectral range realized by metastable electronic states in $\rm Na_2[Fe(CN)_5NO] \cdot 2H_2O$ (1996)
    Springer
    Applied physics 63 (1996), S. 243-248 
    Details
    ISSN: 1432-0649
    Keywords: PACS:42.40.Pa; 42.70.Gi; 42.70.Ln
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Phase and amplitude gratings in the visible and near-infrared spectral range can be written in SodiumNitroPrusside (SNP), $\rm Na_2[Fe(CN)_5NO] \cdot 2H_2O$ , single crystals by optical excitation of infinitely long-living metastable electronic states, localized in the $\rm [Fe(CN)_5NO]^{2-}$ anions. Hence, its photorefractive effect does not depend on dopants or defects. The refractive index is modulated by more than $\Delta n = 1 \times 10^{-3}$ in the red $(632.8$ nm) and $\Delta n = 5 \times 10^{-4}$ in the near-infrared region $(1047$ nm). The absorption coefficient is modulated by about $\Delta \alpha = 100$ m $^{-1}$ at $632.8$ nm and 40 m $^{-1}$ at 1047 nm. The wavelength dependence of $\Delta n$ can be explained by strong absorption bands in the ultraviolet considering Kramers-Kronig dispersive analysis. The time constant of the write-read-erase processes and the diffraction efficiency $\eta$ depend on light intensity, wavelength and polarization of the light with respect to the crystallographic axes. After excitation of the metastable states the indicatrix is modulated only along the $a$ - and $b$ -axis of the orthorhombic system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01833793
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Holographic recording by excitation of metastable electronic states in Na2[Fe(CN)5NO]·2H2O: a new photorefractive effect (1999)
    Springer
    Applied physics 68 (1999), S. 877-885 
    Details
    ISSN: 1432-0649
    Keywords: PACS: 33.80.-b; 42.40.E; 42.65.H; 42.70.Ln
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Elementary holographic phase gratings can be written in single crystals of Na2[Fe(CN)5NO]·2H2O, sodiumnitroprusside, by excitation of metastable electronic states in the blue–green spectral range. For light polarized parallel to the crystallographic a and b axes of the orthorhombic crystal the light-induced modulation of the refractive index reaches Δn≈2×10-3 at λ=514.5 nm. Although the largest population of the metastable states is reached for light polarized parallel to the crystallographic c axis, a photorefractive response is not observed. In contrast to electro-optic photorefractive materials the photorefractive effect depends mono-exponentially on the exposure and on the modulation of the incident light interference pattern. Beam-coupling experiments demonstrate that written gratings are in phase with the interference pattern in correspondence with the fact that the excitation of the metastable electronic states is local. The width of the rocking curve shows that the holographic gratings are written completely over the volume of the crystal. Variations of the wavelengths within the excitation range as well as of the crystal thickness do not influence the maximum photorefractive response. Investigations on the grating vector of the written gratings show unambiguously that charge migration is not responsible for the photorefractive effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003400050718
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Phase gratings in the visible and near-infrared spectral range realized by metastable electronic states in Na2[Fe(CN)5NO] · 2H2O (1996)
    Springer
    Applied physics 63 (1996), S. 243-248 
    Details
    ISSN: 1432-0649
    Keywords: 42.40.Pa ; 42.70.Gi ; 42.70.Ln
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Phase and amplitude gratings in the visible and near-infrared spectral range can be written in SodiumNitro-Prusside (SNP), Na2[Fe(CN)5NO] · 2H2O, single crystals by optical excitation of infinitely long-living metastable electronic states, localized in the [Fe(CN)5NO]2− anions. Hence, its photorefractive effect does not depend on dopants or defects. The refractive index is modulated by more thanΔn = 1 × 10−3 in the red (632.8 nm) andΔn = 5 × 10−4 in the near-infrared region (1047 nm). The absorption coefficient is modulated by aboutΔα = 100 m−1 at 632.8 nm and 40 m−1 at 1047 nm. The wavelength dependence ofΔn can be explained by strong absorption bands in the ultraviolet considering Kramers-Kronig dispersive analysis. The time constant of the write-read-erase processes and the diffraction efficiencyη depend on light intensity, wavelength and polarization of the light with respect to the crystallographic axes. After excitation of the metastable states the indicatrix is modulated only along thea- andb-axis of the orthorhombic system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01833793
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
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