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  • 1
    Electronic Resource
    Electronic Resource
    Poling dynamics and investigation into the behavior of trapped charge in poled polymer films for nonlinear optical applications (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 6834-6842 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The behavior of surface and trapped charge that originate during contact electric-field poling of a model guest–host nonlinearly active polymer has been investigated. Charge effects in thin films of para-nitroaniline doped polymethylmethacrylate were studied during and after the poling process by simultaneous measurement of the current through the poling circuit and the second harmonic generation (SHG) signal from the polymer system. The poling current present in a fresh sample was found to differ in both magnitude and temporal dependence to that observed in the sample during subsequent polings. The magnitude of the steady-state current eventually reached during the poling process was found to depend on temperature and is related to the mobility of charge. A sharp drop-off in SHG signal intensity that occurred when the poling electrodes were grounded is shown to result from the removal of surface charge that orients chromophore dipoles near the surface of the film; the decay in the macroscopic polarization that then occurs is prolonged by charges trapped in the polymer matrix. The build-up of trapped charge explains a memory effect in which the SHG signal relaxation time gradually increased as the film was subjected to multiple polings until a steady-state value was reached. Finally, it is demonstrated that the charges trapped in the polymer matrix are released only after the polymer is heated to high above its temperature of glass transition and the SHG signal has completely decayed away. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471350
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  • 2
    Electronic Resource
    Electronic Resource
    Hyper-Rayleigh scattering using 1907 nm laser excitation (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1277-1284 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The experimental setup used to perform hyper-Rayleigh scattering at the near infrared wavelength of 1907 nm is described. The setup described is employed to measure the first molecular hyperpolarizabilities, β, of three new thiophene-based nonlinear optical chromophores. Although scattering at this wavelength is weak and the experiment requires great care, use of it allows one to obtain near dispersion-free first hyperpolarizability. Comparing the results with those obtained on the same chromophores using the 1064 nm excitation, we show that the two state model, which is commonly used to relate the β values at different wavelengths, fails to correlate the results at these two excitation wavelengths. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149586
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  • 3
    Electronic Resource
    Electronic Resource
    Determination of first hyperpolarizability of nonlinear optical chromophores by second harmonic scattering using an external reference (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 7821-7829 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: First hyperpolarizabilities (β) of two tricyanovinylthiophene nonlinear optical chromophores were determined using second harmonic, hyper-Rayleigh, scattering. The use of an external standard in the determinations is compared with the previous use of an internal standard. The first hyperpolarizability of the well-known chromophore 4 dimethylamino 4′ nitrostilbene (DANS) was also determined using the external standard method and its value is compared to those in the literature. A new method of analyzing the hyper-Rayleigh scattering signal by recording a histogram of the scattered energy is reported. This method is shown to give more reliable results in a shorter period of time than the usual static gate method. The histogram function provides additional information in the form of the histogram width which is shown to be an indication of the mean-square concentration fluctuations of the chromophores in solution. The effects of molecular interactions on the concentration dependence of the hyper-Rayleigh scattering signal is discussed. It is shown that depending on the concentration range, the β value of para-nitroaniline, used as the external standard, can agree with two different values reported in the literature. Results on the depolarization ratio of the hyper-Rayleigh scattered light from one of the tricyanovinylthiophene chromophores are presented. At low concentration the depolarization ratio agrees with the theoretically predicted value based on C2v symmetry. However, at higher concentration the measured depolarization ratio increases indicating molecular interactions. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471669
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  • 4
    Electronic Resource
    Electronic Resource
    Hyper-Rayleigh scattering studies of first order hyperpolarizability of tricyanovinylthiophene derivatives in solution (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 6400-6405 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: First order hyperpolarizabilities, β, for donor–acceptor substituted heteroaromatic compounds are measured by the hyper-Rayleigh scattering technique. Hyper-Rayleigh scattering utilizes the mechanism of number density fluctuations and enables the second harmonic generation signal of nonlinear optical chromophores to be generated as scattered light. Effects of substituting different electron donating groups to the parent heteroaromatic compounds and different solvents on the hyperpolarizability is investigated using this technique. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469355
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  • 5
    Electronic Resource
    Electronic Resource
    Investigation of dipolar reorientation dynamics of pure bulk polymers using second harmonic generation (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 2615-2624 
    Details
    ISSN: 0887-6266
    Keywords: second harmonic generation ; correlated dipolar orientation ; trapped charges ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Second harmonic generation (SHG) in three corona-poled, pure, bulk polymers is studied as a function of temperature. It is found that this technique readily yields dynamical information that is complementary to that obtained from the technique of dielectric relaxation (DR). The SHG results are compared to those from DR in the same temperature ranges above Tg. It is found that in the temperature ranges examined, the relaxation times obtained from SHG are several orders fo magnitude longer than those measured by dielectric relaxation. This is explained as being due to the strong correlation between oriented dipoles and to trapped charges injected by the poling process. Fitting measured data to the Williams-Landau-Ferry (WLF) equation indicates that more free volume is needed in SHG for dipolar reorientation than is needed in DR. An SHG relaxation elongation phenomenon at constant temperature is found to occur in the pure bulk polymers and is similar to that found in chromophore-doped polymers previously studied. The SHG technique is developed as a new tool to directly study the reorientational dynamics of polar polymer segments. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090321607
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