Kotlyar Victor V, Stafeev Sergey S, Liu Yikun, O'Faolain Liam, Kovalev Alexey A
Image Processing Systems Institute of the Russian Academy of Sciences, Samara 443001, Russia.
Appl Opt. 2013 Jan 20;52(3):330-9. doi: 10.1364/AO.52.000330.
By decomposing a linearly polarized light field in terms of plane waves, the elliptic intensity distribution across the focal spot is shown to be determined by the E-vector's longitudinal component. Considering that the Poynting vector's projection onto the optical axis (power flux) is independent of the E-vector's longitudinal component, the power flux cross section has a circular form. Using a near-field scanning optical microscope (NSOM) with a small-aperture metal tip, we show that a glass zone plate (ZP) having a focal length of one wavelength focuses a linearly polarized Gaussian beam into a weak ellipse with the Cartesian axis diameters FWHM(x)=(0.44±0.02)λ and FWHM(y)=(0.52±0.02)λ and the (depth of focus) DOF=(0.75±0.02)λ, where λ is the incident wavelength. The comparison of the experimental and simulation results suggests that NSOM with a hollow pyramidal aluminum-coated tip (with 70° apex and 100 nm diameter aperture) measures the transverse intensity, rather than the power flux or the total intensity. The conclusion that the small-aperture metal tip measures the transverse intensity can be inferred from the Bethe-Bouwkamp theory.
通过将线偏振光场分解为平面波，表明焦斑上的椭圆强度分布由电场矢量的纵向分量决定。考虑到坡印廷矢量在光轴上的投影（功率通量）与电场矢量的纵向分量无关，功率通量横截面呈圆形。使用带有小孔径金属尖端的近场扫描光学显微镜（NSOM），我们表明焦距为一个波长的玻璃波带片（ZP）将线偏振高斯光束聚焦成一个弱椭圆，笛卡尔坐标轴直径半高宽FWHM(x)=(0.44±0.02)λ 和FWHM(y)=(0.52±0.02)λ ，焦深DOF=(0.75±0.02)λ ，其中λ 是入射波长。实验结果与模拟结果的比较表明，带有中空金字塔形镀铝尖端（顶角70°，孔径直径100 nm）的NSOM测量的是横向强度，而不是功率通量或总强度。小孔径金属尖端测量横向强度这一结论可从贝塞 - 鲍坎普理论推导得出。
