Study On The Electro-optic Polymers For Broadband Terahertz Generation

The key point of terahertz technology is to search the high quality generation materials.The terahertz signal is mainly due to the properties of the generation materials.We studied the synthesis of different kinds of chromophores and electro-optic(EO) polymers in order to research their terahertz properties and find out the structure-property relationship.In this dissertation,we firstly introduce the recent progress on EO polymers for terahertz generation and the factors affecting the corresponding terahertz signals. Compared to the conventional crystals used in THz generation,EO polymers have many distinct advantages,such as higher electro-optic coefficients,larger coherence lengths,good phase matching conditions and processibility.As a result,EO polymers are very attractive for generating strong,broadband and gap-free THz radiation.It is proved that EO polymer is one kind of THz radiation source materials which are full of potential applications and research values.The synthesis of EO polymers is based on the chromophores with high electro-optic coefficients.2-dicyano-3-cyano-4,5,5-methyl-2,5-dihydrofuran(TCF), which has strong electron-withdrawing group was prepared by simple methods;four chromophores with active hydroxyl(NLO-l,NLO-2,NLO-3,NLO-4)were prepared, by changing electron-withdrawing groups(-NO₂,TCF),conjugated chain length(-N= N,-CH=CH-) and different conjugated bridges(benzene,thiophene).The structures were also characterized.Presently,the doped systems are mainly used in the THz radiation source materials.In this dissertation,different kinds of side-chain EO polymers were prepared,including polyurethane-imide,polyurethane and epoxide resin.We synthesized a series of novel side chain of polyurethane polyimides by chromophore NLO-1,benzophenone-3,3',4,4'-tetracarboxylic(BTDA) and dianhydridetoluene diisocyanate(TDI) in two steps.Polyurethanes were prepared by NLO-2 and NLO-3 which functioned in the side chain.Epoxide resin EO polymers BP-ABA-TCF were prepared by Knoevenagel reaction with aldehyde group and TCF.At the same time, each chromophores prepared were doped with APC to make the doped systems.We prepared thin films of doped system and side-chain polymer system by spin-coating method.Relevant factors,such as solvent,solution concentration, spin-coating speed and time are discussed as well.We studied the conditions of corona poling and the polarization of thin films.The degree of dipole orientation of the material before and after poling was also studied.It is proved that side-chain polymer system has better orientation stability than doped system.