Bahlmann K, Hell SW
High Resolution Optical Microscopy Group, Max-Planck-Institute for Biophysical Chemistry, D-37070 Gottingen, Germany.
J Microsc. 2000 Oct;200 (Pt 1):59-67. doi: 10.1046/j.1365-2818.2000.00739.x.
Electromagnetic focusing theory of light predicts that at high apertures field components arise that are polarized perpendicular to the initial polarization. Although vectorial depolarization has received considerable attention in focusing theory, no evidence has been presented as to its relevance in experiments. We measure the intensity of the perpendicularly orientated field in the focal region by utilizing monomolecular, fluorescent polydiacetylene layers whose transition dipoles are orientated in a single direction. For a 1.4 numerical aperture oil objective lens illuminated with linearly x-polarized light, we find that the integral of the modulus squared of the y-polarized focal field amounts to 1.5% of its x-polarized counterpart. In particular, we show here that the depolarization increases when using annular apertures. Annuli formed by a central obstruction with a diameter of 89% of that of the entrance pupil raise the integral to 5.5%. This compares well with the value of 5.8% predicted by electromagnetic focusing theory; however, the depolarization is also due to imperfections connected with focusing by refraction. Besides fluorescence microscopy and single molecule spectroscopy, the measured intensity of the depolarized component in the focal plane is relevant to all forms of light spectroscopy combining strong focusing with polarization analysis.
光的电磁聚焦理论预测，在高孔径下会出现垂直于初始偏振方向偏振的场分量。尽管矢量去极化在聚焦理论中受到了相当多的关注，但尚未有证据表明其在实验中的相关性。我们通过利用单分子荧光聚二乙炔层来测量焦区内垂直取向场的强度，该层的跃迁偶极子沿单一方向取向。对于用线性x偏振光照射的数值孔径为1.4的油浸物镜，我们发现y偏振焦场模平方的积分相当于其x偏振对应物的1.5%。特别是，我们在此表明，使用环形孔径时去极化会增加。由直径为入射光瞳直径89%的中心障碍物形成的环将积分提高到5.5%。这与电磁聚焦理论预测的5.8%的值相当吻合；然而，去极化也归因于与折射聚焦相关的不完善之处。除了荧光显微镜和单分子光谱学外，焦平面上去极化分量的测量强度与所有将强聚焦与偏振分析相结合的光光谱学形式都相关。
