Molecular orientation sensitive second harmonic microscopy by radially and azimuthally polarized light.
Molecular orientation sensitive second harmonic microscopy by radially and azimuthally polarized light.
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DOI：
10.1364/boe.5.002231
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发表时间：
2014-07
影响因子：
3.4
通讯作者：
T. Ehmke;T. Nitzsche;Andreas Knebl;A. Heisterkamp
中科院分区：
文献类型：
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作者：
T. Ehmke;T. Nitzsche;Andreas Knebl;A. Heisterkamp
我们论证了通过施加径向和方位偏振入射光来切换高NA物镜焦点附近照明的z偏振分量的可能性。首次通过模拟研究了场分布对非线性效应的影响。这些都是在非线性显微镜中常用的高NA物镜上进行的。特别注意了入射场偏振的影响。对于线偏振光、圆偏振光和径向偏振光，高NA聚焦会在z方向产生相当大的偏振分量。方位偏振是一种例外情况：即使是强聚焦，也不会出现z分量。此外，还计算了输入偏振对产生非线性信号的光强的影响。对于所选择的非线性信号产生阈值，没有发现可比较的输入偏振态之间的明显差异。在天然胶原组织(猪角膜)中对径向和方位偏振涡旋光束产生的信号的差异进行了实验评估。计算结果与理论预测吻合较好，为探索具有已知非线性性质的样品沿光轴方向的分子取向提供了可能。将对材料非线性响应的模拟与不同样品取向和存在或不存在z极化的实验相结合，有助于加深对尚未研究的材料中非线性信号形成的理解。
We demonstrate the possibility to switch the z-polarization component of the illumination in the vicinity of the focus of high-NA objective lenses by applying radially and azimuthally polarized incident light. The influence of the field distribution on nonlinear effects was first investigated by the means of simulations. These were performed for high-NA objective lenses commonly used in nonlinear microscopy. Special attention is paid to the influence of the polarization of the incoming field. For linearly, circularly and radially polarized light a considerable polarization component in z-direction is generated by high NA focusing. Azimuthal polarization is an exceptional case: even for strong focusing no z-component arises. Furthermore, the influence of the input polarization on the intensity contributing to the nonlinear signal generation was computed. No distinct difference between comparable input polarization states was found for chosen thresholds of nonlinear signal generation. Differences in signal generation for radially and azimuthally polarized vortex beams were experimentally evaluated in native collagen tissue (porcine cornea). The findings are in good agreement with the theoretical predictions and display the possibility to probe the molecular orientation along the optical axis of samples with known nonlinear properties. The combination of simulations regarding the nonlinear response of materials and experiments with different sample orientations and present or non present z-polarization could help to increase the understanding of nonlinear signal formation in yet unstudied materials.