Abstract
By performing the femtosecond-pulsed [Formula: see text]-scan experiments at a wavelength of 780[Formula: see text]nm, we report the observation of simultaneous third- and fifth-order refractive nonlinearities in the film of a side-chain azobenzene copolymer synthesized by free-radical polymerization method. Theoretically, we extend two continuous wave [Formula: see text]-scan theories suitable for the excitation of ultrafast laser pulses. First one is valid only for the situation of the sample with the pure third-order refractive nonlinearity. Second one is applicable when the sample exhibits the simultaneous third- and fifth-order refractive nonlinearities. Both [Formula: see text]-scan theories allow the precise analysis of femtosecond-pulsed [Formula: see text]-scan experimental data. Using the femtosecond time-resolved optical Kerr effect measurements, we estimate the nonlinear response time of the sample to be in the sub-picosecond regime. The physical mechanisms of the observed nonlinearity are also discussed. The high nonlinear figure of merit with ultrafast response in this polymer is desirable in nonlinear photonic devices.
Published Version
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