H. Hörhold

Travelling-wave lasing of TPD solutions and neat films

Abstract The travelling-wave lasing action (amplified spontaneous emission (ASE)) of the electrically active triphenylamine dimer N , N ′-diphenyl-bis(3-methylphenyl)-biphenyl-4,4′-diamine (TPD) in 1,4-dioxane solution and as neat film is studied. The samples are transversally pumped with picosecond excitation pulses (wavelength, 347.15 nm; duration, 35 ps). Lasing occurs at 401 nm for TPD in 1,4-dioxane and at 418 nm for TPD neat films. For the photo-physical characterization, the optical constants of neat films are determined by reflection and transmission measurement, the absorption cross-sections are extracted, and fluorescence spectroscopic parameters are determined. The fluorescence quantum yield of TPD in 1,4-dioxane is 0.69 and for neat TPD films, the fluorescence quantum yield is 0.31.

Experimental investigations and numerical simulations of spatial solitons in planar polymer waveguides

Abstract We investigated the beam propagation in a planar polymer waveguide. The conjugated polymer used in our experiments is a solution processable polyarylene-vinylene derivative, the DP-PPV/DP-PFV copolymer, which exhibits both a high focusing Kerr-like nonlinearity and an outstanding light and air stability. We report the first experimental observation of spatial solitons in a polymer waveguide. The corresponding spectral broadening could be detected. To obtain a deeper understanding of the experimental results we carried out numerical simulations of the spatial-temporal objects under investigation. The numerical simulations agree quite well with the experimental findings.

Nonresonant n2 and two-photon-absorption dispersion measurements of DPOP-PPV and DP-PPV/DP-PFV polymer strip waveguides

Abstract A very stable and accurate semi-integrated Mach-Zehnder interferometer setup, that was used to obtain the sign and magnitude of the nonlinear coefficient n 2 of two different main chain organic poly(phenylene-vinylene) polymer derivatives in the wavelength region between 880–990 nm, is presented. The nonlinear refractive index coefficient n 2 is of the order of 10 −14 cm 2 /W for both polymers. Power dependent transmission measurements provided the two-photon absorption coefficient β. It ranges from almost zero to 0.16 cm/GW depending on the wavelength. The results show that the poly(phenylene-vinylene)-derivatives are promising candidates for opto-optical waveguide switching elements.

REFLECTION ELECTRO-OPTICAL MEASUREMENTS ON ELECTROLUMINESCENT POLYMER FILMS : A GOOD TOOL FOR INVESTIGATING CHARGE INJECTION AND SPACE CHARGE EFFECTS

We present experimental results on the electro-optic response of electroluminescent polymer films, pertaining to the family of the poly-phenylene-vinylenes. The samples used in the experiments were obtained by sandwiching polymer films between chromium-gold and indium tin oxide electrodes. The technique that was adopted is based on the Teng and Man setup, that is usually adopted for the determination of the electro-optic Pockels coefficient in poled polymers. As the structure of the polymer used is not provided with polar groups and, moreover, is completely disordered and therefore centrosymmetric, as expected, only quadratic electro-optical effects were observed (Kerr), which are connected to the presence of third-order optical nonlinearities (χ(2)≡0,u2009χ(3)≠0). The existence of charge injection and trapping in the samples, giving rise to built-in static electric fields in the polymer layers, is put into evidence. The experimental data show the presence of a third-order susceptibility for Kerr electro-optic effect which is comparable to values reported in literature, namely χ(3)(−ω;ω,0,0)=7.9×10−21u2009m2/V2 at the wavelength λ=0.6328u2009μm. The possibility that the measured signals are due to a mechanical compression of the films is taken into account and discarded on the basis of the experimental results. The technique can be usefully applied in order to perform charge injection and trapping measurements in electroluminescent devices. Moreover, the results show that in the case of measurements performed on poled polymers for χ(2) applications, the measured values for the electro-optic coefficient can be offset by a third-order contribution, even in those cases when usually one assumes it may be neglected. In the article, the main models reported in literature, describing the effects contributing to the electro-optic response, are critically reviewed. The measurement on the centrosymmetric polymer films were used in order to check those models and permit us to evaluate.We present experimental results on the electro-optic response of electroluminescent polymer films, pertaining to the family of the poly-phenylene-vinylenes. The samples used in the experiments were obtained by sandwiching polymer films between chromium-gold and indium tin oxide electrodes. The technique that was adopted is based on the Teng and Man setup, that is usually adopted for the determination of the electro-optic Pockels coefficient in poled polymers. As the structure of the polymer used is not provided with polar groups and, moreover, is completely disordered and therefore centrosymmetric, as expected, only quadratic electro-optical effects were observed (Kerr), which are connected to the presence of third-order optical nonlinearities (χ(2)≡0,u2009χ(3)≠0). The existence of charge injection and trapping in the samples, giving rise to built-in static electric fields in the polymer layers, is put into evidence. The experimental data show the presence of a third-order susceptibility for Kerr electro-opti...

Spectral broadening measurements in poly(phenylene vinylene) polymer channel waveguides

In a polyconjugated main chain polymer strip waveguide the nonlinear, nonresonant refractive index n2 was measured by monitoring the signal spectrum broadening due to self-phase modulation. The two photon absorption coefficient α2 was obtained by calibrating the inverse transmission measurement. The nonlinear coefficients were determined to be n2=0.85×10−14u2002cm−2/W andα2=0.08 cm/GW at a wavelength λ=885.6 nm. The used polymer was poly[1,4-phenylene1,2-di(phenoxyphenyl)vinylene]. The result is in good agreement with interferometer measurements. The material is suitable for all-optical switching.