THEORY OF 2ND-HARMONIC GENERATION IN RANDOMLY ORIENTED SPECIES
THEORY OF 2ND-HARMONIC GENERATION IN RANDOMLY ORIENTED SPECIES
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DOI：
10.1016/0301-0104(94)00333-6
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发表时间：
1995-01-01
期刊：
影响因子：
2.3
通讯作者：
DEMIDOV, AA
中科院分区：
文献类型：
--
作者：
ANDREWS, DL;ALLCOCK, P;DEMIDOV, AA
众所周知，二次谐波是原子和分子流体中被禁止的过程。然而，最近对随机取向的盐生盐杆菌紫色膜悬浮液中二次谐波演化的实验观察提出了新的问题，即确定禁止二次谐波的准确标准。为了解决这个问题，发展了一个专门处理分子系统的倍频理论框架，因此更多地考虑了局部结构的影响，并根据分子性质进行了预测。这与基于体磁化率的经典方法形成对比，后者已被证明不足以解释相互矛盾的实验结果。通过适当地描述处理必要的方向平均的详细过程，本理论揭示了二次谐波的相干过程与其非相干对应的定向分量超瑞利散射之间的关系，并解释了在紫膜悬浮液中检测到的倍频现象。文中还讨论了谐波演化的偏振特性，特别是证明了在圆偏振泵浦条件下倍频信号将持续存在。这种特殊的偏振特性将允许对该理论进行实验验证。
It is well known that second harmonic generation (SHG) is a process forbidden within atomic and molecular fluids. Nonetheless recent experimental observations of second harmonic evolution in suspensions of randomly oriented Halobacterium halobium purple membranes have raised new questions about the precise criteria which determine prohibition of the second harmonic. To address the problem a theoretical framework for SHG is developed that specifically deals with molecular systems, and is therefore cast in terms of molecular properties with more regard to the influence of the local structure. This contrasts with the classical approach based on bulk susceptibilities, which has not proved adequate to explain the conflicting experimental results. By properly formulating the detailed procedure for dealing with the necessary orientational averages, the present theory discloses a relationship between the coherent process of second harmonic generation and a directed component of its incoherent counterpart, hyper-Rayleigh scattering, Inter alia, the theory explains the SHG detected in purple membrane suspensions. The polarisation features of the harmonic evolution are also considered more generally, and in particular it is shown that the SHG signal will persist under conditions of circularly polarised pumping. This specific polarisation feature will allow experimental validation of the theory.