以单光束偏振倍频理论为基础，研究了在手性实验装置中当起始入射光和倍频出射光的偏振态均为线性时，与p+s偏振倍频光信号相关的非零实验展开系数f，g 和h 的唯一性。研究结果表明，对于具有D-π-A型结构的有机光学材料分子，当采用s和p±s等类型线偏振起始光时，实验拟合展开系数唯一，而p线偏振起始光情况的拟合系数却不唯一，相应p+s线偏振倍频探测的模拟信号能够完全解释实验结果与早期理论预示之间的矛盾。为了精确确定D-π-A型结构材料的所有二阶非线性极化率张量元，在手性实验装置中避免使用p偏振起始光是非常有必要的。

Based on single-beam polarization second-harmonic generation, when polarizations of both initial input beam and second- harmonic output beam are linearly polarized in chiral experimental setup, uniqueness of nonzero experimental fitting expansion coefficients f，g and h related to p + s- polarized second- harmonic signal is reported. The results indicate that for organic optical molecules with D- p- A structured, these experimental expansion coefficients are unique for s- and p±s-polarized initial beams, but they are not unique for p- polarized initial beam, and the simulated results of the p + s- polarized second- harmonic signal can completely explain the contradiction between theory and experiment. To precisely characterize all the secondorder nonlinear susceptibility tensor components of the D- p- A structured materials, it is necessary to avoid using the p-polarized initial beam in a chiral experimental setup.