Electromagnetic trapping of chiral molecules: orientational effects of the irradiating beam
Electromagnetic trapping of chiral molecules: orientational effects of the irradiating beam
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DOI：
10.1364/josab.32.000b25
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发表时间：
2015-05
影响因子：
1.9
通讯作者：
D. S. Bradshaw;D. Andrews
中科院分区：
文献类型：
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作者：
D. S. Bradshaw;D. Andrews
通常负责分子的电磁捕获的光子相互作用是前向瑞利散射，这是由连接基态电子态和虚拟激发态的过渡电偶极子介导的过程。高阶电磁多极子对散射振幅的贡献通常可以忽略不计。然而，考虑到手性识别效应（其中左手圆偏振的输入光与右手偏振相比可以呈现不同的可观测量，或者相反对映体形式的分子对设定的圆偏振的响应不同），该机制必须扩展到专门适应过渡磁偶极子。此外，重要的是要考虑到手性分子必然是非球形的，因此它们与激光束的相互作用将具有取向依赖性。使用量子电动力学，本文量化的程度时，手性分子被光学捕获的能量歧视，特别强调的捕获光束的取向效应。一个复杂的整体加权方法，用于将后者的深入描述。因此，它表明，当分子对映异构体的混合物被照射的圆偏振光的连续光束，不同的出现在每一个对映异构体的迁移的相对速率的最强的区域的光束。因此，光学捕获可用作实现对映体分离的手段。
The photonic interaction generally responsible for the electromagnetic trapping of molecules is forward-Rayleigh scattering, a process that is mediated by transition electric dipoles connecting the ground electronic state and virtual excited states. Higher order electric and magnetic multipole contributions to the scattering amplitude are usually negligible. However, on consideration of chiral discrimination effects (in which an input light of left-handed circular polarization can present different observables compared to right-handed polarization, or molecules of opposite enantiomeric form respond differently to a set circular polarization), the mechanism must be extended to specifically accommodate transition magnetic dipoles. Moreover, it is important to account for the fact that chiral molecules are necessarily nonspherical, so that their interactions with a laser beam will have an orientational dependence. Using quantum electrodynamics, this article quantifies the extent of the energetic discrimination that arises when chiral molecules are optically trapped, placing particular emphasis on the orientational effects of the trapping beam. An in-depth description of the intricate ensemble-weighted method used to incorporate the latter is presented. It is thus shown that, when a mixture of molecular enantiomers is irradiated by a continuous beam of circularly polarized light, a difference arises in the relative rates of migration of each enantiomer in and out of the most intense regions of the beam. As a consequence, optical trapping can be used as a means of achieving enantiomer separation.