No abstract

Linear and nonlinear optical properties of a new soluble polymer bearing distyrylbenzene chromophore, the alkoxysulphono-substituted p-phenylenevinylene oligomer (MTPV-ORSO) attached as a side-chain to the methyl methacrylate backbone are reported. This chromophore was developed for introduction into single-mode nonlinear optical polymer fibres. The molecular second-order and third-order nonlinearities were estimated with quantum chemical calculations (MOPAC). The side-chain polymer shows an optical absorption maximum at 326 nm. The polymer was incorporated into the core of the fibre preform with a procedure which led to a step index profile, as measured with a preform profiler, suitable for a single-mode optical fibre. Second harmonic of the fundamental 1200 nm wave was measured in the corona poled polymer films giving the second-order susceptibility d 33 = 0.8 pm/V for the polymer containing about 1.3 wt. % of the side-chain chromophore and 0.1 pm/V in a guest-host system containing 0.24 wt. % of the chromophore in the fibre preform. The coherence length of the side-chain polymer, equal to 28 µm at 1200 nm, was evaluated from the dispersion of the linear refractive indices. Degenerate four-wave mixing (DFWM) with amplified femtosecond pulses was also applied to measure the nonlinear refractive index of the co-polymer at 800 nm.

Time-resolved DFWM experiments were performed with 150 fs pulses at 800 nm in chloroform solutions of π-conjugated molecules: p-bis(o-methylstyryl)-benzene (Bis-MSB) and a newly synthesized derivative of distyrylbenzene: an oligomer of pphenylenevinylene substituted in the para position with electron donating alkyleneoxy group bearing the methacrylic group and an electron accepting 2-ethylhexylsulfonyl group (MTPV-SOHE monomer). The asymmetric substitution causes a red shift (24 nm) of the absorption maximum and enhancement of third-order optical susceptibility. The second hyperpolarizability derived from a quadratic dependence of the phase matched DFWM signal on concentration of MTPV-SOHE was about 6 times bigger than that in Bis-MSB.

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