, Volume 27, Issue 5, pp 411-420

Second-harmonic generation in poled films of nonlinear optical polymer composites

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The second-harmonic generation (SHG) has been measured for studying the molecular ordering and its relaxation process in poled states of two different nonlinear optical (NLO) polymer composites.p-Nitroaniline (pNA) and the azo dye Disperse Orange 3 (DO3) are uniformly dispersed in photopolymer matrices followed by poling. Two different composites made-up of 1 wt% of pNA and 2.5 wt% of DO3 are poled at 200 MV m-1 and 80 MV m-1, respectively. One of the second-order NLO coefficients,d 33, was found to be 0.27 pm V-1 for the pNA-doped film and 0.20 pm V-1 for the DO3-doped film. While for the latter the ratiod 33/d 33 (∼3.1) is consistent with the value of 3 in the low-field approximation, for the former the value of 3.5 indicates that higher-order effects of the poling field play a significant role in the NLO process. It is suggested that the SHG relaxation dynamics is also closely related to the UV absorption of the NLO molecules in a photopolymer matrix.