芪类分子掺杂极化聚合膜的非线性光学性质

采用实时测量光学二次谐波产生（SHG）和吸收光谱的方法时芪类有机分子DANS（4’－N，N－dimethylamino－nitrostilbene）及一种新合成的经氰基团修饰的有机分子CNDS（α’－cyano－4’－nitro－4－N,N－dimethylaminostilbene）掺杂PMMApoly（methylmethacrylate）]极化聚合膜的非线性光学性质进行了研究。在电晕极化条件下，由于聚合膜的电导率随温度的变化急剧增加，实验中发现两种掺杂极化聚合膜的最佳电导极化温度均低于它们的玻转温度Tg．在最佳极化条件下，从极化前和极化后的吸收光谱变化可看出CNDS的有序度较DANS的差．但实时SHG表明，CNDS／PMMA极化掺杂聚合膜的二阶非线性系数X（2）较DANS／PMMA极化聚合膜的大．结合极化前和极化后吸收峰强度的变化，我们得到CNDS分了的非线性极化率β约为140×10-30esu.在撤离极化场后，CNDS／PMMA的SHG强度的弛豫也比DANS／PMMA慢，说明CNDS是一种性能较DANS优越的制备二阶光学非线性的掺杂分子．

Improved Optical Nonlinearity of Poled Stilbene Doped Polymer Films

The optical properties of corona poled 4'-N,N-dimethylamino-mtrostilbene (DANS) and a newly synthesized α'-cyano-4'-mtro-4-N.N-dimethylaminostilbene (CNDS) doped poly(methyl methacrylate) (PMMA) films were investigated with in situ second-harmonic generation (SHG) measurement and absorption measurement. Optimum corona poling temperatures of these polymer films were found lower than glass transition temperatures of the materials, most probably due to the dramatically increased conductivity of the films and phase separation. Under the optimum corona poling condition, the alignment ordering of CNDS was lower than that of DANS from the absorbance before and after corona poling. But the second-order nonlinear susceptibility X(2) of CNDS/PMMA is improved compared with that of DANS/PMMA. The molecular second-order polarizability β of the CNDS/PMMA was estimated to be about 140×10-30 esu from the measured absorbance and X(2). The relaxation of SHG intensity of CNDS/PMMA was slower than that of DANS/PMMA. This showed that CNDS is a kind of better dopant than DANS as second -order nonlinear-optical materials.