Some novel multi-dimensional charge-transfer (CT) chromophores, 2-[4-(4,5-di(4-nitrophenyl) imidazolyl)phenyl]-4,5-di(4-aminophenyl)imidazole (DNPIPDAPI), 2-[4-(4,5-di(4-nitrophenyl)imidazolyl)phenyl]-4,5-di(4-metho xy phenyl)imidazole(DNPIPDMOPI) and 2-[4-(4,5-di(4-nitrophenyl) imidazolyl) phenyl]-4,5-di(4-hydroxy-phenyl) imidazole(DNPIPDHPI) were designed and synthesized. And the polyimide was formed with one of the novel chromophores(DNPIPDAPI) and (formula available in paper). The thermal and temporal stability of the poling induce orientation were evaluated. The temporal orientation of the poled polyimide film with DNPIPDAPI was over 1000 hours at 150°C retaining 85% of the initial d33value. Comparing with 1-D chromophores, the synthetic multiple CT chromophore possesses better property in controlling the decay of the SHG activity.
Optical limiting property of two types of charge transfer salt [M(DMID)2][C]x and [M(DMIT)2][C]x (M = Ni, Cu) (C=TMA, TBA) is studied. The comparison of these two series complexes demonstrates that the optical limiting effect of the Ni-based complexes is better than that of the Cu-based complexes, both of them are a little less than that of C60. The nonlinear absorption coefficient that determined by optical limiting technique for Ni-based complexes is about one order of magnitude higher than that of Cu-based complexes. On the other hand, partial charge transfer may enhance the optical limiting effect in the Cu-based complexes, but it doesn't occur in the Ni-based complexes. All may be attributed to the typical column structure that caused by plan configuration.
Photorefractive film of low Tg polymer composites of poly(N-vinylcarbazole): -(4-nitrophenyl)-(1)-prolinol: 2,4,7-trinitro-9-fluorenone: N-ethylcarbazol was fabricated at a weight ratio of PVK:NPP:TNF:ECZ equals 35:50:1:15 wt percent. Two-beam-coupling (TBC) experiment and four-wave mixing experiment were performed at wavelength of 633nm. A reversible photorefractive grating and an irreversible grating, were observed and distinguished. The TBC coefficient was measured to be 140 cm-1 at E0 equals 85 V/micrometers , corresponding to a photorefractive grating of 3.6 X 10-3. The irreversible grating was measured to be about 7 X 10-3, which was attributed to the NPP aggregation.
A polymethyl methacrylate (PMMA) and N-(4-nitrophenyl)-(s)- prolinol (NPP) side-chain polymer waveguide was developed and corona poled for second-harmonic generation (SHG) devices. The nonlinearity decreases with time in the corona poled NPP polymer waveguide were characterized by the variation of the extraordinary and the ordinary refractive indices with time. The Cerenkov-type green second-harmonic (SH) radiation at 532 nm was observed successfully.
The dot products (mu) g(beta) CT of first hyperpolarizability and ground state dipole moment of two merocarbocyanines: 3-ethyl-5-[2-(3-ethyl-2- benzothiazolinylidene)ethylidene]rhodanine (dye I) and 3- cyano-5-[2-(3-ethyl-2-benzothiazolinylidene)- ethylidene]-4-phenyl-2(5H)-furanone (dye II) were measured experimentally with the Solvatochromism and compared to the values obtained by Am1/FF calculation. The comparable result was also obtained by the measurement of second harmonic generation for LB film of dye II. The (mu) g(beta) CT of dye II is larger than that of the famous NLO chromophore 4- N,N-dimethylamino-4-nitrostilbene (DANS). Through the calculation of the heat of formation of two dyes' various isomers, it is found that the most stable one is the (cis- ,cis-) isomer which possesses the largest (beta) value. The origin of large (beta) values for dyes has been explained based on the two-level model from the investigation of the extended molecular conjugation length, change of charge distribution between the ground and first excited state and the analysis of the frontier molecular orbitals. In addition, Dye I is a quasi-two-dimensional chromophore while Dye II is a one- dimensional one, which can be explained by whether the electron-withdrawing group in dyes has mesoionic ring characteristic or not.
Poled polyureasulfone thin films having excellent transparency from near UV to visible region have been prepared by carrying out additional polymerization of 1,4- phenylene diisocyanate and 4,4'-diaminodiphenyl sulfone simultaneously with poling. The polymerization process is monitored by in-situ second harmonic generation. Under optimal conditions, d33 as large as 8.5 pm/V at a second harmonic wavelength of 532 nm has been obtained. SHG intensity decreased to about 84% of its initial value after having been kept at 100 degrees Celsius for over 1000 hours. Wavelength dispersion measurement of SHG coefficients indicates that d33 of prepared poled films increases by about a factor of three at a second harmonic wavelength of 400 nm.
The preparation and corona-poling process of NPP [N-(4- nitrophenyl)-(s)-prolinol] side-chain polymer waveguides was developed, and its optimum process parameters were given in this paper. The dispersion and nonlinear decaying properties of the poled polymer waveguides were studied for the design and fabrication of waveguide frequency doubling devices.
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