Investigation On Nonlinear Optical Properties Of Fluorine And Benzothiadiazole Copolymer With Triphenylamine Derivative Side Chain

The development of nonlinear optics need study of nonlinear optical material.The polymer brought considerable attention of people,as which possess many excellent features,such as varied molecular structure,effortless processing,adjustable nonlinear optical properties and so on,compared with other materials.The polymer with excellent nonlinear optical properties and flexible molecular structure will widely applied to optical switches,optical bistability and optical optical limiting devices.In this dissertation,nonlinear optical properties of a new copolymer of fluorine and benzothiadiazole with triphenylamine derivative side chain(BCT)is investigated by top-hat Z-scan by means of picosecond and nanosecond laser pulses at the wavelength of 532 nm.We found that the BCT exhibits strong reverse saturable absorption(RSA)and selfdefocusing.By using optical limiting experiment we found out that the BCT transmittance drop rapidly with the increase of the laser energy,which show that the BCT can be appled to optical limiting components.By fitting the experimental results with theory of Z-scan,the nonlinear absorption coefficient and the nonlinear refraction coefficient is obtained.To studied sample's nonlinear absorption and nonlinear refraction dynamics,a picosecond rime resolved pump-probe experiments have been performed at 532 nm on the BCT.By a five-energy-level model and experimental result,we know that nonlinear of the BCT root in single photon excited state absorption and analyze out the response process.Based on five-level model and with the help of ns Z-scan,a series of nonlinear optical parameters are calculated out.Using femtosecond transient absorption spectra(TAS)between 480 nm and 780 nm,we discover the BCT possess good nonlinear absorption effect in the between 480 nm and 780 nm originated from excited state absorption.by femtosecond Z-scan experiment in different wavelength,we found that the BCT have the best nonlinear absorption property in 532 nm.