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  • 1
    Electronic Resource
    Electronic Resource
    Non-steady-state photoelectromotive force in reduced lithium niobate crystals (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2389-2392 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Non-steady-state photocurrents are generated in reduced iron-doped lithium niobate crystals. Dependences on spatial frequency and on modulation amplitude are well described by the existing theory and a Debye screening length of 19 nm is determined. The non-steady-state photocurrents strongly decrease for frequencies above 2 Hz. The technique might be useful for material characterization and for convenient active stabilization of holographic setups against mechanical vibrations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371065
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  • 2
    Electronic Resource
    Electronic Resource
    Stabilized recording and thermal fixing of holograms in photorefractive lithium niobate crystals (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 1591-1594 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Holograms are thermally fixed in photorefractive lithium niobate crystals, i.e., they are recorded at temperatures between 130 and 180 °C. The setup is actively stabilized during recording against movements or vibrations of the interference pattern which especially occur during long-period writing at enhanced temperatures. Two different techniques are investigated: (1) Interference of the recording beams using one crystal surface as a beamsplitter yields a signal for stabilization. (2) Alternatively, one of the beams is periodically phase modulated and the beam-coupling signal is used for stabilization. Reproducible refractive index changes of thermally fixed holograms up to 7.5×10−4 are obtained with both stabilization techniques. However, the second method is advantageous for multiplexing experiments, because no readjustment of the beam-coupling stabilization system is required if the angles of the recording beams are changed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148814
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  • 3
    Electronic Resource
    Electronic Resource
    Photoconductivity of photorefractive Sr0.61Ba0.39Nb2O6:Ce crystals at high light intensities (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 251-255 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method is presented to perform direct photoconductivity measurements of Sr0.61Ba0.39Nb2O6:Ce crystals at high intensities: A high voltage is applied to the sample and subsequent illumination yields a photocurrent through the crystal which charges a capacitor. Finally an electrometer measures the voltage of this capacitor. From voltage, capacity and exposure time the photoconductivity is calculated. Measurements with light pulses of a Q-switched frequency-doubled Nd:YAG laser (pulse duration 20 ns, light wavelength 532 nm) are performed. The photoconductivity σph increases sublinearly with light intensity I according to σph∝Ix with x〈1. The experimental results point to Ce3+/4+ as the dominant photo- refractive center in Sr0.61Ba0.39Nb2O6:Ce at high intensities. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362812
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  • 4
    Electronic Resource
    Electronic Resource
    Non-volatile holographic storage in doubly doped lithium niobate crystals (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 393 (1998), S. 665-668 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Photorefractive materials are being widely investigated for applications in holographic data storage. Inhomogeneous illumination of these materials with an optical interference pattern redistributes charge, builds up internal electric fields and so changes the refractive index. Subsequent ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/31429
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  • 5
    Electronic Resource
    Electronic Resource
    Light-induced charge transport processes in photorefractive barium titanate doped with rhodium and iron (1996)
    Springer
    Applied physics 63 (1996), S. 315-321 
    Details
    ISSN: 1432-0649
    Keywords: PACS:61.72.-y; 72.40.+w; 78.20.-e
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Absorption, light-induced absorption changes, photo and dark conductivities, bulk photovoltaic currents and two-beam coupling gain coefficients are measured for oxidized, as grown and reduced BaTiO $_3$ :Rh,Fe crystals. The oxidized sample shows hole conductivity and three photorefractive levels are present: h $^{4+/5+}$ , Fe $^{4+/5+}$ and Rh $^{3+/4+}$ . The measurements indicate that Rh $^{3+/4+}$ is responsible for the photo conductivity and that its energy level is located $(0.9 \pm 0.1)$ eV above the valence band edge. The as grown sample also shows hole conductivity and two photorefractive levels are involved: Rh $^{3+/4+}$ and Fe $^{3+/4+}$ . The results yield that the Fe $^{3+/4+}$ level is located $(0.95 \pm 0.05)$ eV above the valence band edge. In the reduced sample electrons are the dominant charge carriers and two levels are of importance. The shallow one is located $(0.39 \pm 0.05)$ eV below the conduction band edge. Here the performance of this crystal is strongly impaired by a pronounced sublinear photo conductivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01828733
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  • 6
    Electronic Resource
    Electronic Resource
    Light-induced charge transport processes in photorefractive crystals I: Models and experimental methods (1997)
    Springer
    Applied physics 64 (1997), S. 273-291 
    Details
    ISSN: 1432-0649
    Keywords: PACS: 61.70; 72.20; 72.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003400050175
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  • 7
    Electronic Resource
    Electronic Resource
    Three-valence charge-transport model for explanation of the photorefractive effect (1995)
    Springer
    Applied physics 61 (1995), S. 27-32 
    Details
    ISSN: 1432-0649
    Keywords: 61.70 ; 72.40 ; 78.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new charge-transport model assuming one center in three different valence states is discussed for explanation of the photorefractive effect. Quantitative description of experimental results in KNb03:Fe by the model is demonstrated. Many similarities with the so-called “two-center” model are found although the microscopic explanation of the light-induced charge transport is rather different.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01090968
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  • 8
    Electronic Resource
    Electronic Resource
    Light-induced charge transport processes in photorefractive barium titanate doped with rhodium and iron (1996)
    Springer
    Applied physics 63 (1996), S. 315-321 
    Details
    ISSN: 1432-0649
    Keywords: 61.72.-y ; 72.40.+w ; 78.20.-e
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Absorption, light-induced absorption changes, photo and dark conductivities, bulk photovoltaic currents and two-beam coupling gain coefficients are measured for oxidized, as grown and reduced BaTiO3:Rh,Fe crystals. Theoxidized sample shows hole conductivity and three photorefractive levels are present: Rh4+/5+ Fe4+/5+ and Rh3+/4+. The measurements indicate that Rh3+/4+ is responsible for the photo conductivity and that its energy level is located (0.9 ± 0.1) eV above the valence band edge. Theas grown sample also shows hole conductivity and two photorefractive levels are involved: Rh3+/4+ and Fe 3+/4+. The results yield that the Fe3+/4+ level is located (0.95 ± 0.05) eV above the valence band edge. In thereduced sample electrons are the dominant charge carriers and two levels are of importance. The shallow one is located (0.39 ± 0.05) eV below the conduction band edge. Here the performance of this crystal is strongly impaired by a pronounced sublinear photo conductivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01828733
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  • 9
    Electronic Resource
    Electronic Resource
    Light-induced charge transport processes in photorefractive crystals II: Materials (1997)
    Springer
    Applied physics 64 (1997), S. 391-407 
    Details
    ISSN: 1432-0649
    Keywords: PACS: 61.70; 72.20; 72.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: 3 , LiTaO3, BaTiO3, Ba1-xSrxTiO3 ( , BST), Ba1-xCaxTiO3 ( , BCT), KNbO3, KTa1-xNbxO3 ( , KTN), Sr1-xBaxNb2O6 ( , SBN) and Bi12(Si,Ti,Ge)O20 (BSO, BTO, BGO) are discussed. Utilizing the knowledge on the charge transport processes, consequences for applications are deduced; improved techniques for nondestructive readout of holograms with light of the recording wavelength are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003400050190
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  • 10
    Electronic Resource
    Electronic Resource
    Light–induced charge transport processes in photorefractive barium titanate crystals doped with iron (1997)
    Springer
    Applied physics 65 (1997), S. 481-487 
    Details
    ISSN: 1432-0649
    Keywords: PACS: 61.72.-y; 72.40.+w; 78.20.-e
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: 3 ) are annealed in a hydrogen atmosphere at various temperatures. After these reducing treatments, absorption, light–induced absorption changes, two–beam coupling direction, photo electron paramagnetic resonance (photo EPR), dark and photoconductivity as well as bulk photovoltaic current density are investigated. The samples are electron conductive and the charge transport is governed by only one level, which is identified by photo EPR as Fe2+/Fe3+. The photoconductivity exceeds the dark conductivity for intensities above 1 kWm-2. A relation between the absorption constant and the Fe2+ concentration is derived. From the known charge transport parameters the advantageous photorefractive properties of optimized reduced BaTiO3:Fe are deduced; possible response times in the millisecond range at an intensity of 10 kWm-2 are estimated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003400050300
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